Basic Mud Logging

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(1)Basic Mud Logging Guide Version 2.0.

(2) Basic Mud Logging. INTRODUCTION The drilling rig is a complex system consisting of people and equipment who must work safely under extreme conditions. The rigs can range from a truck mounted work-over rig to a large ocean going drill ship. Rigs are primarily divided into two major categories; land and marine. It is important to be cognizant of each rig type so that you as a logging engineer will be able to competently participate in the safe and hopefully productive completion of the well. The drilling rig and personnel perform very special functions at different times. In the oil field, the customary unit of measure of rig production is the foot. In many parts of the world the meter is used in place of the foot; a meter equals about 3.281 feet. The foot is a convenient unit by which to measure the product of a drilling operation and pay the contractor who drilled or “made the hole.” It is a fact of life in the drilling industry, however, that the cost per foot of making hole varies directly in relation to the depth to which the foot of hole is drilled. The deeper the hole, the more costly each additional foot drilled. Most rigs are owned by an individual or a firm known as a drilling contractor. Companies engaged in finding, producing, or refining petroleum, own the majority of leases, or wells. These companies are often called operators, or operating companies. Representing the operator is the company man or drilling supervisor. The operator hires or contracts, the drilling contractor to drill the well. In most cases, drilling contracts are drawn on a day work basis, which means that payment is made for each day the rig is used, plus certain extras. Both the operator and the contractor are interested in such details as the time required for completing the job; the safety of the equipment, property, and personnel throughout the operation; and the ability of both the men and the equipment to do acceptable work. The mud logging engineer needs to become familiar with the basic equipments, techniques and terms used in drilling operations. Although he has no direct responsibility for the drilling or the rig, the mud logging engineer has to be conversant with the equipment and procedures so that he can advise on certain aspects and so that he can understand the effects of drilling methods affecting the parameters he uses for his interpretation. It is also important for the mud logging engineer to develop good working relationship with the drilling personnel to keep a two-way flow of information and gain the greatest benefits for the operation. This guide is rather meant as a briefing instruction to those mud logging engineers who are newly involved in rig drilling operations, facing new concepts, routines and formats. It is also tried to introduce and illustrate modern or future development that may be new to some “old hands” with no recent exposure to the actual work. However, owing to the fast development of techniques and methods, even this booklet will be out dated partly in very short time.. PetroServices GmbH Training Center. Page 2 of 196.

(3) Basic Mud Logging. RIG TYPES Drilling rigs are classified according to field operations into two major types (land rigs and off shore rigs) which by turn reclassified into other types depending on each rig capability and working environment. Accordingly, rig type can be one of the followings:.  Land rigs: Land rigs are generally either wheel mounted portables or a component system that must be moved by trucks and cranes. The drilling floor generally sits on top of a steel substructure that could be 30 feet high or more. A drilling mast (derrick) is attached to and raised above the floor. In general, the deeper wells need a larger, taller rig. The mast must be capable of supporting the vertical load and weight of the stacked drill pipe. It must also withstand wind loads of 100 to 130 miles per hour. Shallow wells and wells being completed or repaired will probably use a portable rig. This rig can be driven to the well site, raised up hydraulically and guy wired in place. When the well is completed, the mast is hydraulically lowered and the rig is driven off.. PetroServices GmbH Training Center. Page 3 of 196.

(4) Basic Mud Logging  Offshore rigs: One of the hazards of offshore drilling is the hostile environment. The effects of greater water depths, storms, wave action and uncertain exploratory data all greatly increase the financial risks. The exploratory wells must be drilled and a reserve potential established that could justify these costs. These exploratory wells seek to establish new reservoir locations and sizes. Once drilled and evaluated, the exploratory well is most often plugged and abandoned. This results in the use of marine rigs for offshore drilling. The development wells are usually drilled from fixed platforms specially designed to exploit the reserves of the reservoir. The platform is also used for production facilities after all drilling operations are complete. The environment also determines which type of marine rig will be used. Each rig has advantages and disadvantages when used in different water depths and weather conditions. The type of marine rig also can depend on problems involved in getting the rig on location and keeping it stationed in the desired position. The choices include the jackup rig, semisubmersible rig, the submersible rig, the drill ship, the platform rig, the inland barge rig, and the tension leg platform.. Different types of offshore rigs. PetroServices GmbH Training Center. Page 4 of 196.

(5) Basic Mud Logging 1. Jackup rigs: The jackup rig has replaced the submersible rig as a fixed drilling platform. It is less costly to build and can operate in up to 600 feet of water. It is ideal for soft ocean sediments found in river deltas. The jackup rig consists of a watertight hull and three or more mobile legs. The legs are raised up to allow the vessel to be towed to a location. Then the legs are carefully jacked down until each rests on the seabed. The hull is then jacked up on the legs until it is above the predicted height of storm waves. This height depends on the area and the season. It varies in the Gulf of Mexico from 25 to 35 feet and in the North Sea up to about 95 feet for the worst storm conditions to be expected. Because the jackup also sets on the seabed, it does not have heave problems. It can have vessel motion problems during bad weather if jacked to the top of the legs. This eliminates the need for most motion compensation equipment and special mooring and anchoring equipment. To move rig between close locations the platform is lowered down the legs until it floats then the legs are jacked up to the maximum height. The whole rig can then be towed by means of two boats. In long rig moves or across oceans the whole rig is normally carried on a huge carrier. Disadvantages include its difficulty in towing, especially in rough seas; the legs must be removed during long moves.. Jackup offshore rig. PetroServices GmbH Training Center. Page 5 of 196.

(6) Basic Mud Logging 2. Semi-submersible rigs: Semi-submersible rigs are floating rigs supported on pontoons. A common design consists of four, five or six legs. Older semi-submersibles are kept on location by means of anchors and chains, whereas some of the newer ones are kept on location by means of thrusters. The pontoons can be re-floated to change locations. They can be towed easily or even self-propelled to the new location. The semi-submersible rig evolved from the older submersible rigs. It can provide a relatively stable drilling platform. It can operate under more serve weather and sea conditions and in water depths from 600 to 4,000 feet. The semi-submersible rig contains a normal working deck plus columns and pontoons under the deck. These pontoons are ballasted to a water depth that causes the upper deck to remain high above the water. Semi-submersible rigs are the elephants of the offshore rigs, capable to continue operation in bad weather. Semi-submersible rigs move with the tide the drilling penetration rate must be corrected for the influence of the tidal heave. The disadvantages of semi-submersible rigs are that they require marine risers and a subsea stack, having limited cargo capacity and require support vessels.. Semi-submersible offshore rig. PetroServices GmbH Training Center. Page 6 of 196.

(7) Basic Mud Logging 3. Drill ship: Drill ships are ships specially built and modified to drill in deep water or in operations that are not suitable for semi-submersible rigs. Drill ships are self-propelled and can carry larger loads of drilling supplies. This makes them more mobile and self-supporting in remote ocean areas. The drill ship is capable of drilling in waters up to 9,000 feet. It also offers advantages of faster travel times, are self-propelled, and can use dynamic positioning systems. Drill ships are differentiated from other offshore drilling units by their easy mobility. While semi-submersible rigs can also drill in deep waters, drill ships are able to propel themselves from well to well and location to location, unlike semi-submersible, which must rely on an outside transport vessel to transfer them from place to place. The disadvantages of drill ships include high salaries for the ship’s crew who are not directly involved in the drilling operations. In addition, the drill ship is greatly affected by wave motion (heave) and drifting. This requires a motion compensation system, a marine riser system, and/or a mooring and anchoring system or thrusters for dynamic positioning. Transocean, Pride, Seadrill, Frontier Drilling and Noble are a few of the companies that own and operate drill ships globally.. Drill ship. PetroServices GmbH Training Center. Page 7 of 196.

(8) Basic Mud Logging 4. Platform rigs: If the exploration drilling program is successful in finding a commercial reservoir, a development program must be planned. All facilities needed to drill, produce, store and transport the hydrocarbons must be designed, fabricated and installed on the site. All fixed platforms must be able to withstand the environmental forces of its region. This could include wind, waves, currents, ice, earthquakes and soil conditions. The platform generally consists of four to eight piles or legs resting or driven into the seabed. Drilling slots on the platform are arranged in a grid system. The actual drilling rig will be skidded from slot to slot for each well. The individual wells will be drilled at an angle to allow for efficient production of the reservoir. A fixed drive pipe extends from a subsea template to the substructure of the platform. The BOP stack is connected to the fixed drive pipe for each well slot as it is drilled. Because of its location, the stack is easier to install, repair or change sizes.. Offshore platform. PetroServices GmbH Training Center. Page 8 of 196.

(9) Basic Mud Logging 5. Inland barge rigs: A drilling structure consisting of a barge upon which the drilling equipment is constructed. When moved from one location to another, the barge floats. When stationed on the drill site, the barge can be anchored in the floating mode or submerged to rest on the bottom. Typically, inland barge rigs are used to drill wells in marshes, shallow inland bays, and areas where the water covering the drill site in not too deep. Also called swamp barge. The inland barge rig is the oldest form of marine rig. It consists of two hulls, which are connected by legs. The upper hull is air tight and provides the buoyancy necessary to float the rig to each site. The rig is positioned over the site and the lower hull is flooded. This causes the rig to sink until it rests on the sea floor. After drilling the well, the rig is re-floated and moved to a new location. The inland barge rig is limited to working in relatively shallow water, less than 50 feet normally. They are also hard to move to new locations.. Inland barge rig. PetroServices GmbH Training Center. Page 9 of 196.

(10) Basic Mud Logging 6. Tension leg platforms: The Tension Leg Platform is one of the newest types of rig available. It is a combination of a semi-submersible rig and a platform rig. It is used strictly for production drilling. Normally, some of the wells in the field have already been drilled, and then the TLP is positioned over the pre-drilled wells and the production lines run to the existing wellheads. They are set up with drilling equipment in the event other wells need to be drilled, or any existing wells must be worked over. The current technology allows the TLPs to work in up to 5,000 feet of water. The platform is permanently moored by means of tethers or tendons grouped at each of the structure's corners. A group of tethers is called a tension leg. A feature of the design of the tethers is that they have relatively high axial stiffness (low elasticity), such that virtually all vertical motion of the platform is eliminated. This allows the platform to have the production wellheads on deck (connected directly to the subsea wells by rigid risers), instead of on the seafloor. This allows a simpler well completion and gives better control over the production from the oil or gas reservoir, and easier access for downhole intervention operations. TLP's have been in use since the early 1980s. The first Tension Leg Platform was built for Conoco's Hutton field in the North Sea in the early 1980s. Larger TLP's will normally have a full drilling rig on the platform with which to drill and intervene on the wells. The smaller TLPs may have a workover rig, or in a few cases, no production wellheads located on the platform at all.. Tension leg platform rig. PetroServices GmbH Training Center. Page 10 of 196.

(11) Basic Mud Logging. LAND RIG COMPONENTS Simple diagram of a land drilling rig and its components is illustrated in the next figure. The typical rig shown in the next figure shows the layout of most component parts. Use this layout as you read about each system on the rig. Not all rigs are arranged the same. Newer rigs use modular designs and space saving techniques.. The main rig components are as follow: 1. Crown Block and Water Table 2. Cat-line Boom and Hoist Line 3. Drilling Line 4. Monkey board 5. Traveling Block 6. Top Drive 7. Mast 8. Drill Pipe 9. Doghouse 10. Blowout Preventer 11. Water Tank 12. Electric Cable Tray 13. Engine Generator Sets 14. Fuel Tanks 15. Electric Control House 16. Mud Pump 17. Bulk Mud Components Storage 18. Mud Pits 19. Reserve Pits 20. Mud Gas Separator 21. Shale Shaker 22. Choke Manifold 23. Pipe Ramp 24. Pipe Racks 25. Accumulator. Land rig components. However, all rigs must have five basic systems or operations performed. These include: 1. Hoisting system: used to raise and lower drill pipe, casing, and tubing. 2. Circulating system: used to remove cutting and maintain pressure in the well bore. 3. Rotating system: used to turn the drill stem to make hole. 4. Power production system: used to produce mechanical and electrical power. 5. Blowout prevention system: used to seal off the well bore to control formation fluids.. PetroServices GmbH Training Center. Page 11 of 196.

(12) Basic Mud Logging 1. Derrick or mast: A standard derrick is a structure with four supporting legs resting on a square base. It can be assembled piece by piece each time a well is drilled. In contrast, the mast is assembled once when it is manufactured. After manufacture, it remains a single unit each time a well is drilled. When a mast is raised and lowered, it looks something like the blade of a huge jackknife being opened and closed. As a result, masts are sometimes referred to as jackknife masts. For most offshore drilling rigs, the derrick is the standard.. The mast or derrick is erected on substructure that serves two main purposes:. a. 1. To support the rig floor, providing space for equipment and workers. 2. To provide space under the rig floor for special, large valves called blowout preventers. The substructure supports not only the rotary table, but also the full load of the drill string when the string is suspended in the hole by the slips. It also supports a string of casing when the casing is being run in the hole by an arrangement of slips resting on the rotary. The rig floor also holds the draw works, the driller’s control panel, the doghouse, and other related equipment. Derricks and masts are rated according to the vertical load they can carry and the wind velocity they can withstand from the side. Derrick loadbearing capacity figures may vary from 250,000 to 1,500,000 pounds. A typical mast or derrick can withstand winds of about 100 to 150 miles per hour with the racks full of pipe and without the need for external bracing. The derrick and its substructure support the weight of the drill string at all times, whether the drill string is suspended from the crown block or resting in the rotary table. The height of a derrick does not affect its load-bearing capacity, but the length of the sections of drill string to be removed from the hole is limited by the height of the derrick. This is because the crown block must be sufficiently elevated above the rig floor to permit the withdrawal and temporary storage of the drill string when it is pulled from the well to change bits or for other reasons. Drill pipe is pulled and racked in stands. A stand usually consists of three joints of pipe, each about 30 feet long. Such a stand, having a total length of some 90 feet, can be accommodated in a derrick that is 136 feet high or higher. Rigging-up time is the time spent to assemble a mast into the vertical position on-site. It also includes the time to install the power unit, all cables and piping. Masts are used for lighter work.. PetroServices GmbH Training Center. Page 12 of 196.

(13) Basic Mud Logging 2. Hoisting system: The draw works, sometimes called the hoist, is a big heavy piece of machinery that consists of a revolving drum around which the wire rope, called the drill line, is spooled or wrapped. It also has a cat-shaft, a kind of axle that crosses through the draw works that has a revolving drum (called a cat-head spool) on both end and two special cat-heads. Several other shafts, clutches, and a chain-and-gear drive facilitate speed and direction changes. An integral part of the draw works is a system of speed changes (transmission system). This transmission system as shown in the next figure gives the driller a wide choice in hoisting the pipe. Thus, the drum of the hoist may be considered as having a minimum of four and often as many as eight speeds.. Draw work transmission system. PetroServices GmbH Training Center. Draw work system. Page 13 of 196.

(14) Basic Mud Logging The origin of the term draw works is not actually known, but probably is related to the fact that part of the function of the draw works is to draw pipe out of the hole. The two main purposes of the draw works are: 1. To lift pipe out of the hole. 2. To lower the pipe back into the hole. Wire rope is reeled, or spooled, on a drum in the hoist. When the draw works is engaged, the drum turns and, depending on the direction it either turns, reels in the drill line to raise the traveling block or lets out the line to lower it. Since the drill string is attached to the block by the elevators, the string is thus raised or lowered. One of the outstanding features of the hoist is the brake system, which enables the driller to easily control a load of thousands of pounds of drill pipe or casing. On most rigs, there are at least two brake systems. One brake is mechanical and can bring the entire load to a full stop. The other brake is hydraulic or electric and can control the speed of the descent of a loaded traveling block, although it is not capable of bringing it to a complete halt. Another feature of the draw works is the cat-shaft with its two special cat-heads. The makeup (spinning) cat-head on the driller’s side of the draw works is used to spin up and tighten the drill pipe joints. The other, located opposite the driller’s position on the draw works, is the breakout cat-head. It is used to loosen the drill pipe when the pipe is withdrawn from the hole.. Draw works cat-head PetroServices GmbH Training Center. Page 14 of 196.

(15) Basic Mud Logging 3. Blocks and drilling line: The traveling block, crown block, and drilling line are the three components whose function is to support the load of drill pipe in the derrick as it is lowered into or pulled from the hole. During drilling operations, this load consists of the hook, swivel, kelly, drill pipe, drill collars, and a bit attached to the bottom of the drill collars. During cementing operations, a string of special pipe called casing, often a heavier load than the drill pipe and drill collars, has to be lowered into the hole and cemented. Drill line is usually made of wire rope that generally ranges from 1.5 inches to 1.75 inches in diameter. Wire rope is similar to common fiber rope, but wire rope, as the name implies, is made of steel wires and is a complex device.. Although the wire rope looks very much like cable, it is specially designed for the heavy loads encountered on the rig. To achieve the greatest economy from the use of wire on a drilling rig, the line selected should be in accord with both the load requirements and the design of the sheaves in the traveling block and crown block through which the line must travel. The line should be frequently inspected to ensure that it is in good condition. The drill line should be moved periodically (slipped in the field term) so that it wears evenly as it is used. Cut off procedures should take into account the amount of usage or work done by the wire rope. Wire rope wear is determined by the weight, distance, and movement of wire rope travel over a given point (ton-miles). Traveling block The drill line is threaded over a crown block sheave and lowered down to the rig floor. On the rig floor rests (temporarily) another very large set of pulleys or sheaves called the traveling block. The end of the line is threaded through one of the traveling block sheaves and is raised again up to the crown block. There the line is threaded over a sheave in the crown block, lowered back down, and threaded through the traveling block. This is done a number of times until the correct number of lines has been strung up. The number of lines, of course, is only one; but, since the drill line is threaded through the crown block and traveling block several times, it gives the effect of many lines. The number of lines strung depends on the weight to be supported. The more weight to be supported, the more lines that are needed and vice versa. Once the last line has been strung over the crown block sheaves, the end of the line is lowered down to the rig floor and attached to the drum on the draw works. Several wraps of line are then taken around the draw works drum. The part of the drill line running out of the draw works up to the crown block is called the fast line; “fast” because it moves as the traveling block is raised or lowered on the derrick. The end of the line that runs from the crown block down to the supply reel is then secured. This part of the line is called the deadline; “dead” because, once it is secured, it does not move. Mounted on the rig substructure is a device called a deadline anchor. The deadline is firmly clamped to the anchor.. PetroServices GmbH Training Center. Page 15 of 196.

(16) Basic Mud Logging 4. Elevators: Two elevators are hung from the hook on the elevator bails and are used for latching around the drill pipe in order to lift it. Elevators are of many slightly differing designs and sizes for use with different pipe sizes, drill collar and casing sizes. They are not used during the drilling operation but are necessary for lifting the pipe during tripping operation. Elevators are a set of clamps that are latched onto the drill pipe to allow the driller to raise or lower the drill string out of or into the hole. The driller lowers the traveling block and the elevators down to a point where the drill crew can latch the elevators onto the drill pipe.. 5. Slips: These devices are used to hold the weight of the drill string when it is not supported by the hook (during connections or tripping time). Slips are made of hinged sections with a single opening. They are placed around the pipe, their tapered outer sections fitting against either the inside surface (bowl) or the master bushing or against the inserts. As the pipe is lowered, the slips tapered section causes them to close tightly around the pipe. The downward motion of the drill pipe must be stopped with the draw works brakes, not with the slips. The drawing shows the effects of stopping the motion of the pipe with slips. This can occur when the floor hands are not careful to set the slips at the proper time when the driller has stopped the pipe. Do not let the slips "ride" on the pipe while the pipe is being pulled out of the hole. This practice accelerates the wear on the gripping elements of the slip. It also risks having the slip ejected from the master bushing bowl when a tool joint comes through and causing possible injury to personnel. Be careful not to catch the tool joint box in the slips when the driller slacks off. This often happens when coming out of the hole and the driller does not pick up high enough for the slips to fall around the pipe properly. This can ruin the slips, damage the tool joint box and damage the body of the pipe.. PetroServices GmbH Training Center. Page 16 of 196.

(17) Basic Mud Logging 6. Rotating equipments: The rotating equipment from top to bottom consists of the swivel, the kelly, the rotary table, the drill string and the bit. The drill string is the assembly of equipment between the swivel and the bit, including the kelly, drill pipe and drill collars. The term drill string simply refers to the drill pipe and drill collars; however, in the oil field, drill string, is often used to mean the whole works.  Swivel: The swivel is a remarkable mechanical device; it is attached to the traveling block by a large bail. The swivel has three main functions: 1. It supports the weight of the drill string. 2. It allows the drill string to rotate. 3. It provides a pressure tight seal and passageway for the drilling mud to be pumped down the inside of the drill string. The fluid comes in through the gooseneck, a curved pipe that connects the swivel to a hose (kelly hose) carrying the drilling fluid from the mud pumps. The fluid then passes through the wash pipe, a vertical tube in the center of the swivel body, and into the kelly and drill string.. Swivel. PetroServices GmbH Training Center. Drill string. Page 17 of 196.

(18) Basic Mud Logging  Kelly and rotary table: The kelly is a three, four, or six-sided length of pipe, about 50 feet long, that is the upper part of the drill string. It serves as a passageway for the drilling fluid on its way into the hole and transmits the rotary movement to the drill pipe and bit. An upper kelly cock is a special valve that can often be recognized as a bulge on the upper part of the kelly. The kelly cock can be closed to shut off well pressure coming up from inside the drill string. Most kelly cocks require a special wrench to operate the closing valve. A lower kelly cock (also called a drill pipe safety valve or a drill string valve) is usually made up between the lower end of the kelly and the top joint of drill pipe. When the kelly is pulled up high above the rotary table, as it usually is when a joint of pipe is being added to the drill string (i.e., when a connection is being made), the upper kelly cock cannot be reached easily should it be necessary to close in the drill string. However, the lower kelly cock is readily accessible when the kelly is raised. The kelly’s upper end is connected to the swivel, and its lower end is connected to the drill pipe. The drill pipe screws into a device called a kelly saver sub, or a saver sub. The sub is a short, connecting fitting that screws into the bottom of the kelly. The bottom threads on the sub are temporarily joined with threads on the top of each length of drill pipe that is added to the string. The sub saves wear on the threads of the kelly; when the threads of the sub become worn, the sub is replaced and rethreaded. The kelly fits into a corresponding square or hexagonal opening in a device called a kelly, or drive bushing. The kelly bushing fits into a part of the rotary table called the master or rotary bushing. As the rotary bushing rotates, the kelly rotates; and as the kelly rotates the drill string and bit. Rotary drilling derives its name from the rotary table. The rotary table is powered by the compound or by its own electric motor.. Rotary table. PetroServices GmbH Training Center. Page 18 of 196.

(19) Basic Mud Logging  Top drive system: The top drive system is replacing the kelly and rotary table on many rigs. This one piece of equipment replaces both the kelly and rotary table. The basic model is an equipment with one pinion powered by a hydraulic motor located on top of the gearbox. Top drive system advantages: • •. •. • •. • • • • • •. • •. The top drive make-ups and breaks-out many connections, thereby reducing the hazards of rotary tongs and spinning chain. The pipe handling features use hydraulic arms to move drill pipe and drill collars to and from the V-door and monkey board, thereby reducing strenuous work and increasing pipe handling safety. The automatic, driller operated pipe elevators eliminate accidents caused by drilling crews operating elevators manually during under balanced drilling operations. The top drive increases safety by reducing BOP wear and allowing the BOP/rotating head to pack off against round tubulars, not a square or hex Kelly. Well control capability is greatly enhanced because of the ability to screw into the string any point in the derrick to circulate drilling fluids. Remote operated Kelly valve reduces (optional) mud spillage when back reaming or breaking off after circulating above the rig floor. Reduce total drilling costs by increasing drilling efficiency. No drilling downtime caused by the inability to engage the kelly bushing in the rotary table. Eliminate time lost due to picking up or racking back the swivel and kelly when going from tripping to drilling or vice versa. Increase penetration rates when spilling in or drilling the surface hole. Eliminate rat hole contractor charges and costs of rat hole, mouse hole and conductor pipe in many cases. Make connections on the bottom while directional drilling, eliminating the need to re -orient the tool face after each connections. Spend more time on bottom making the hole and less time making connections, tripping, surveying, reaming and other non drilling rig functions. Continuous rotation and circulation during full movement of The Drill String. The most important feature of the top drive is the ability to rotate and pump continuously while reaming into or out of the hole. Continuous rotation means substantially reduced friction when removing the string from or tripping back into directional or horizontal wells. Top drive system. PetroServices GmbH Training Center. Page 19 of 196.

(20) Basic Mud Logging  Drill string: The drill string is made up of the drill pipe and special, heavy-walled pipe called drill collars. Each length of drill pipe is about 30 feet long and is called a joint of pipe. Each end of each joint is threaded. The end of the joint with the interior threads is known as the box, and the end of the joint with the exterior threads is called the pin. When pipe is made up, the pin is stabbed into the box and the connection tightened. The threaded ends of the pipe are called tool joints and are actually separate parts that are welded onto the ends of the drill pipe by the manufacturer who cuts the threads to industry specifications. Drill collars, like drill pipe, are steel tubes through which mud can be pumped. Drill collars are heavier than drill pipe and are used on the bottom part of the drill string to put weight on the bit. This weight presses down on the bit to get it to drill. Drill collars are about 30 feet long and, unlike the drill pipe that has tool joints welded on, they have the boxes and pins cut into them.. Heavy weight drill pipes. PetroServices GmbH Training Center. Drill collars. Page 20 of 196.

(21) Basic Mud Logging  Stabilizers: These are run between the drill collars and are of a blade type construction. Drilling fluid can pass freely between the blades while the outer edge of the blades contacts the wall of the hole and holds the drill collars firmly centered in the hole. They do exactly as their name implies, they provide stability to the bit and collars. This is important as it improves bit life, in addition to keeping the direction of the hole under control. The purpose of the stabilizers is to centralize the collars and to keep the hole straight. The faces of the stabilizer fins are coated with hard material such as tungsten carbide to reduce wear and tear..  Reamers: Reamers usually have the same diameter as the bit and run a little distance above it. The reamer function is to cut the hole out to full size behind the bit. There are many types of reamers depend on the formation that they will pass through. For example, roller reamers are classified into three roller cutter types: • Soft formation cutters deliver maximum reaming action in soft formations like soft limestone and shale. Service life of cutter is enhanced with hard end and carburized teeth. • Medium to hard formation cutters are most suitable for cherty formations to hard formations such as dolomite, hard limestone and chert. • Very hard formation cutters deliver reliable reaming performance in hard, abrasive and semi-abrasive formations such as granite and sand.  Bumper Sub: Bumper subs are currently used in offshore operations to permit a constant weight to be carried on the bit while drilling, regardless of the vertical motion imparted to the drill pipe by drilling vessel heave. The vertical motion of the lower end of the drill pipe (the bumper sub end) may be appreciably greater than the vessel heave. Therefore, the necessary stroke of bumper subs for successful operation is greater than thought in the past. In addition, there is an appreciable tendency of the drill pipe to buckle above the unbalanced type of bumper sub. Thus, more drill collars than previously used should be carried above unbalanced bumper subs to keep drill pipe straight.. PetroServices GmbH Training Center. Page 21 of 196.

(22) Basic Mud Logging  Rotary & crossover sub: Rotary subs have two primary applications. They can be used to crossover from one connection size to another or as the disposable component used to extend the connection life of a more expensive drill stem member. Rotary subs are available with box x pin, box x box or pin x pin connections. The rotary subs include the following types: Straight OD sub is used to connect drill string members that have a similar outside diameter. The drill bit, downhole tools, heavy weight drill pipe and drill pipe can be crossed over using a straight OD sub. Reduced section sub is used to connect drill stem members that have different diameters that warrant the cross-sectional change necessary to accommodate different connections. This sub would be used to crossover large OD drilling tools or a tapered drill collar string. Saver sub is used to extend the life of the kelly by taking the connection wear each time it is made up to a drill string component. The saver sub connection is sacrificed because it can be easily repaired or inexpensively replaced. The saver sub can be equipped with a rubber protector to reduce BOP equipment and casing wear resulting from contact damage with the lower kelly connection..  Top drive sub: Top Drive Subs serve as the sacrificial element between the drill string and the top drive, reducing repair and maintenance costs. The top drive sub can easily be repaired or replaced in the event the lower pin threads become galled or damaged. These tools are manufactured from selected bars of alloy steel, heat treated to provide the strength and toughness required to carry the entire weight of the drill string..  Bent sub: This is a non-straight sub designated with different bending angles, it is fitted in the deviating bottom hole assembly above the mud motor to drill deviated holes. The angle of bending is selected according to the inclination building rate and the length of the interval to be drilled with this sub.  Lift sub: A Lift Sub enables the safe, efficient handling of straight OD tubulars such as drill collars, shock tools, jars, directional equipment and other tools by using the drill pipe elevators. Lifting subs can be either tapered or square shoulder types and are made from AISI 4145/4140. They are available in all diameters and lengths..  Lift plugs: Lift plugs are of heat treated steel alloy. Crown sections are bored out to reduce weight. They are available in all sizes with or without lifting bail.. PetroServices GmbH Training Center. Page 22 of 196.

(23) Basic Mud Logging  Bits: There are many types of bits that have been developed through the years for more efficient drilling. Among these types are: •. Rock bits: Roller cone or rock bits have cone-shaped steel devices called cones that are free to turn as the bit rotates. Bit manufacturers either cut teeth out of the cones or insert very hard tungsten carbide buttons into the cones. The longer the teeth of the bit, the softer the formation need to be and vice versa. The teeth can be made of the same material as the cones (milled teeth) or made of hard (e.g. tungsten carbide) inserts, hence insert bits. The teeth are responsible for actually cutting or gouging out the formation as the bit is rotated. All bits have passages drilled through them to permit drilling fluid to exit. Most bits have nozzles that direct a high-velocity stream or jet of drilling fluid to the sides and bottom of each cone so that rock cuttings are swept out of the way as the bit drills.. •. PDC bits: Polycrystalline Diamond Compact (PDC) bits do not have cones, but they do have tungsten carbide teeth. Several hundred diamonds are embedded onto the edges of the teeth. Since diamonds are so hard, diamond bits are especially suited for drilling hard formations but can also be used very effectively on soft formations. Such bits can stay on bottom for a long time and drill long distances. However, on the negative side, PDC bits are extremely sensitive to pyrite in the formation and metal junk as debris that may come from a cast iron casing shoe. In addition, their penetration rate in shale is relatively poor and their cost much higher than the cost of ordinary tricone bits.. PetroServices GmbH Training Center. Page 23 of 196.

(24) Basic Mud Logging 7. Power system: On a diesel engine rig, diesel engines, which on land rigs are usually located at ground level some distance away from the rig floor, drive large electric generators. The generators, in turn, produce electricity that is sent through cables to electric switches and control gears. From here, electricity goes through additional cables to electric motors that are attached directly to the equipment involved in drilling draw works, mud pumps, and the rotary. The diesel-electric system has a number of advantages over the mechanical system. One of the primary advantages is the elimination of the heavy, complicated compound and chain drive, thus eliminating the need for aligning the compound with the engines and draw works. Another advantage is that the engines can be placed away from the rig floor reducing engine noise for the crew.. 8. Mud circulating systems: The drilling fluid (mud) is of great importance to the drilling operation. Whilst drilling, the mud is constantly circulated from the active pits, down through the drill string through the bit, returning up the annulus and back over the shale shaker before returning to the mud pits. The main purposes of circulation are: 1. Transport bit cuttings to the surface. 2. Clean the bottom of the hole. 3. Cool and lubricate the bit and drill string. 4. Support the walls of the wellbore. 5. Prevent entry of formation fluids into the well. Other purposes of circulation are to make it possible to detect gas, oil, or water that may enter the drilling fluid from a formation being drilled; to get information necessary for evaluating producing zones (from cuttings, cores, or electric logs); and to transmit hydraulic power to the bit. In addition, drilling fluid is sometimes used to drive a mud motor that has been placed at the bottom of the drill string. In this case, the drilling fluid provides power to the motor so that the bit turns without engaging the rotary table. Circulating, or drilling fluid is a liquid, it is made up mostly of water, although occasionally oil is the major component. Both types of drilling fluids are called muds, or drilling muds, because that is what they appear to be. Nevertheless, some drilling muds are quite a bit more than just muds; literally, scores of special chemical additives and weighting materials are put into them in order to achieve their purpose with the greatest efficiency. Special clays are used to give body to the mud, and barite (a heavy mineral) is added to increase the density of the mud. Chemicals are used to control the thickness or viscosity of the mud and to improve the ability of the solid particles in the mud to deposit a layer, or cake, on the wall of the hole.. PetroServices GmbH Training Center. Page 24 of 196.

(25) Basic Mud Logging  Mud pumps: The mud is mixed in the mud pits (sometimes called mud tanks) with the help of a mud hopper into which most of the dry ingredients for the mud are poured. The tanks contain agitators (paddle-like projections) that mix the mud. The mud is mixed with either oil or water, depending on the mud properties needed. The mud pump is the primary component of any fluid circulating system. Pumps are either powered by electric motors attached directly to them, or driven by the compound. The pumps for rotary drilling rigs have high ratings and are capable of moving large volumes of fluid at very high pressures. Mud pumps are generally classified into two main types:. •. Triplex pumps:. Triplex pumps are found now almost universally on new rigs because of their better performance. The triplex pump has three pump cylinders operating on one crank shaft with 120 degree phase difference. Every cylinder pumps with the forward moving action of the piston and recharges with the retracting action of the piston. The cylinder liner and the piston of the mud pump can be changed to provide different balances between volume and pressure. It is not uncommon to operate the pumps with 7” liner during the upper portion of a hole, where large mud volumes are required and then change to 6” liner for the deeper portion of the hole, where volume is less important than pressure.. Triplex mud pump. PetroServices GmbH Training Center. Page 25 of 196.

(26) Basic Mud Logging •. Duplex pumps:. Duplex pump has two cylinders operating on one crank shaft with 180 degrees. Each cylinder has two suction and two discharge valves. As the piston moves through the cylinder it is discharging mud in front at the same time as mud is filling the cylinder behind. Similar to triplex pump the cylinder liner and the piston of the mud pump can be changed to provide different balances between volume and pressure. It is not uncommon to operate the pumps with 7” liner during the upper portion of a hole, where large mud volumes are required and then change to 6” liner for the deeper portion of the hole, where volume is less important than pressure.. Duplex mud pump PetroServices GmbH Training Center. Page 26 of 196.

(27) Basic Mud Logging  Shale shaker: Shale shaker is a vibrating screen used to separate the drilled solids from the drilling fluid. The screen is mounted on a spring or rubber supported chassis, which is vibrated by means of an eccentric rotating shaft. Screens of different mesh size are available. Mesh sizes being measured by the number of openings per square inch. The screens are sometimes mounted as a pair, using screens of different sizes. In double deck Shaker; mud returning from the well core comes down the flow line and into a surge tank; sometimes known as the possum belly or shaker header box; this allows a smooth flow of mud onto the screens. The shakers are usually situated over a sand trap, which is a narrow pit with sloping sides terminating in a valve, it is used to trap fine sand that may pass through the shaker screens, and this pit must be dumped out periodically..  Desanders and desilters: These devices remove particles from mud, which were not removed by the shakers or the sand trap. This separation is accomplished by utilizing centrifugal force. The equipment is essentially a series of cones mounted on a manifold; mud is pumped into the manifold and enters the cone. The mud swirls round the inside of each cone, this rotating action causes the lighter fluids to come to one centre and rise out of a hole in the top, whereas the heavier soils go to the outside of the cone and sink down it and out of an opening in the bottom. These units are operated at low pressure (30-40 psi) but can handle high volumes, typically 250 gallons per minute per cone. The difference between desanders and desilters is mainly in the size of the cones. The smaller the cones the smaller the particles that it separates.. PetroServices GmbH Training Center. Page 27 of 196.

(28) Basic Mud Logging  Mud degasser: When wells are drilled into the earth, it occasionally happens that a quantity of natural gas in a formation penetrated by the well bore becomes entrained in the drilling mud thereby reducing the density of the drilling mud and consequently reducing the hydrostatic pressure of the mud in the well bore. When the hydrostatic pressure decreases, gas from any gas bearing formation is more likely to flow into the well bore thereby further cutting the mud and further reducing its density and hydrostatic pressure if this process continues, the mud will become so light that the well blows out. Consequently, mud degassing units have long been employed in the drilling of wells in areas containing high pressure gas formations that act to remove a great deal of the entrained gas from drilling mud. Commercially available mud degassers fall into a variety of types that operate on a variety of different principles. A typical degasser operates on a vacuum principle. The mud is delivered to a vacuum chamber and spread out in relatively thin sheets over a plurality of downwardly inclined plates or leaves. The idea is that when the mud is spread out, and the vacuum is applied to the chamber, the entrained gas comes out of the mud, is picked up by the vacuum pump and discharged from the vacuum chamber. Other types of mud degassers incorporate pumps that pump the gas saturated mud into separating vessels arranged, in some fashion, to separate the entrained gas from the liquid mud. One of the major defects of standard vacuum degassers and those which pump gas cut drilling mud, is that they are arranged to remove mud from the mud tank, degas the mud and then return the mud to the mud tank. The ideal location to degas drilling mud is before it reaches the mud tank because all of the mud in the system can thereby be degassed and there is no dilution of degassed mud with gas saturated mud. The problem is that commercially available degassers operating on the principles they use are incapable of tolerating the drilled solids, which are carried by the mud. One would appreciate that sand grains, bits of shale or limestone pieces are not readily tolerated by those degassers, which use pump to pump the mud into a separating mechanism. Likewise, a conventional vacuum degasser is rapidly filled up with drilled solids because of the small tolerances and gaps inherent in these mechanisms.. PetroServices GmbH Training Center. Page 28 of 196.

(29) Basic Mud Logging 9. Blowout prevention system: Blowout preventers (BOPs) are used to control blowout. The crew usually installs several blowout preventers (BOP stack) on top of the well, with an annular blowout preventer at the top and at least one pipe ram and one blind ram blowout preventer below. Also, some well control techniques require both the annular and the ram blowout preventers. An annular blowout preventer has a rubber sealing element that, when activated, seals the annulus between the kelly, the drill pipe, or the drill collar. If no part of the drill stem is in the hole, the annular blowout preventer closes on the open hole. Ram blowout preventers are large steel rams that have sealing elements. One type of ram blowout preventer is called a pipe ram because it closes on the drill pipe; it cannot seal on open hole. Blind ram blowout preventers are straight-edged rams used to close an open hole. Since BOPs are critically important to the safety of the crew, the rig and the wellbore itself, BOPs are inspected, tested and refurbished at regular intervals determined by a combination of risk assessment, local practice, well type and legal requirements. BOP tests vary from daily function testing on critical wells to monthly or less frequent testing on wells thought to have low probability of well control problems.. Blowout preventer stack PetroServices GmbH Training Center. Page 29 of 196.

(30) Basic Mud Logging 10. Special rig components for floating rigs: A mobile floating rig such as the semisubmersible or drillship is constantly being subjected to vertical and horizontal motions due to wind, waves and currents. The rig must be equipped with a system that automatically compensates for these forces. A marine riser system provides for a flexible path for drilling fluids between the drill floor and the wellbore on the below the sea floor. It also provides a passageway for the drill string and casing down to the BOP stack sitting on the sea floor.  Riser system: The drilling riser system consists of a BOP stack hydraulic connection, lower ball joint, flexible choke and kill lines, riser pipe and connectors, telescopic (slip) joints, diverter system, and a riser tensioner system. Some systems include another annular BOP between the hydraulic connector and the lower ball joint. This preventer can be used to allow replacement of the rubber elements on the other annular BOP in the preventer stack..  BOP stacks: As with all drilling rigs, the offshore rigs are equipped with BOP stacks. The mobile rigs will have the stack mounted on the sea floor below the marine riser. Drilling platforms and jackup rigs will have the BOP stack located in the substructure below the rig floor. The subsea blowout preventers must not only control high pressure formation fluids. They must also be able to close the top of the borehole at the sea floor; disconnect, hang off or cut the drill pipe; and disconnect and reconnect the marine riser system to the wellhead. Modern rigs use single stacks consisting of two annular and four ram-type BOPs in one stack. The total stack may have an 18 ¾-inch bore and 10000-psi or higher working pressure. One ram will contain shear/blind ram blocks for cutting the drill string in case of emergency. PetroServices GmbH Training Center. Page 30 of 196.

(31) Basic Mud Logging  Drill string compensation: The entire drilling rig will heave vertically due to the wave action. The rising deck would pull the entire drill string upward, raising the bit off bottom. As the wave crest passes, the deck would sink rapidly. The rigid drill string would drop and jar the bit on the bottom of the borehole. In addition, the proper amount of weight on bit could not be maintained. Drilling would be impossible and unsafe. The drill string compensation system consists of large cylinders and an air pressure vessel. The cylinders and pistons are placed between the traveling block and the hook suspended in the mast. They are generally capable of stroking 18 feet that is adequate for even high waves. The heave of the drilling rig raises and lowers the fixed portion of the compensator but the relative position of the drill string will remain constant.. PetroServices GmbH Training Center. Page 31 of 196.

(32) Basic Mud Logging. RIG PERSONNEL Whatever job you perform for PetroServices, you will need to know how the drilling process is managed, supervised and completed. Who is in charge? Who can authorize the stopping of drilling? Who can authorize you to visit the rig floor? The chain of command is usually filled with personnel of varying degrees of experience. Those at the top have generally had experience in all phases of rig operations. Those with the least experience are usually found performing specific duties requiring limited training. The drilling bid proposal will contain many important specifications. These will usually include the starting date, depth to be drilled (TD), formations to be penetrated, hole sizes, casing sizes, drilling mud program, logging program, casing program, cementing, testing and well completion. A company representative represents the operating company on the rig site..  Company representative. The company representative is employed by the operating company, and is responsible for all phases of drilling the well and for all needed equipment and services such as casing, drilling mud, logging and cementing. Upon arrival at a rig site, contact the company representative first.  Tool pusher. The tool pusher is in charge of the drilling rig and crews needed in the drilling operations. He is generally an expert in drilling operations and equipment, and is the main liaison between the drilling contractor and the operating company.  Driller. The next highest level of authority on the rig is the driller, who is the working supervisor for the shift. The driller operates the controls on the drill floor. He raises and lowers the drill string, sets the speed and penetration rates, operates the mud pumps and operates the BOP stack as needed. The driller reports to the tool pusher.  Derrick man. The next man in line under the driller is the derrick man. He is experienced enough to assist or relieve the driller. During a trip out of the hole, he will work in the derrick racking the stands of drill pipe. At other times, he may be servicing the mud and mud equipment.  Roughnecks. The roughnecks are the workers who make up and break out the joints of pipe. They work on the floor and keep a steady supply of drill pipe to connect to the drill string. The roughnecks also help maintain other equipment on the rig floor. The roughnecks report to the driller. While drilling, one Roughneck is present in the mud process room at all times. He takes mud weights and ensures shakers and other machines are working properly.  Crane operator. The crane operator is in charge of the loading and unloading of boats. The pipe rack area is also in crane operator’s charge, as are the roustabout crews. The crane operator reports directly to the tool pusher.  Roustabouts. The roustabouts are the workers who help load and unload equipment for the crane operator. They also clean, repair and maintain the rig and its systems. They report to the crane operator.  Subsea engineer. The subsea engineer is responsible for maintaining the subsea blowout prevention system. This includes the wellhead connection, the BOP stack, control system, marine riser system and the motion compensation equipment. PetroServices GmbH Training Center. Page 32 of 196.

(33) Basic Mud Logging  Barge engineer. A floating platform and drillship will have a barge engineer assigned, who is responsible for the stability and ballast of the vessel. The barge engineer must be notified before any heavy equipment is moved or loaded on the rig. He must keep the rotary table in the correct position to drill the hole.  Specialty crewmen. Some skills are needed on the rig full time. These specialty skills include the motorman, rig mechanic, rig welder, and rig electrician.  Service specialists. The operator will contract with special service companies for certain needs. These service crews include well loggers, mud suppliers, analysis and treatment, cementing, casing, wireline operations and others.  Motorman. The motorman is responsible for maintenance of the engines. While all members of the rig crew help with major repairs, the motorman does routine preventive maintenance and minor repairs.. PetroServices GmbH Training Center. Page 33 of 196.

(34) Basic Mud Logging. DRILLING FLUIDS PROPERTIES Definition of a drilling fluid according to API is “a circulating fluid used in rotary drilling to perform any or all of the various functions required in the drilling operation”. The functions of drilling fluids are quit complex and the success of a drilling program depends on the proper understanding and application of these functions. The following functions are the most important functions of drilling fluids during drilling operations..  Cooling the bit and lubricating the drill string: During drilling, considerable heat and friction is built up due to bit contact with the formation. The heat buildup by the continual friction is transmitted to the drilling fluid and circulated to the surface where it is dissipated. The drilling fluid also lubricates the bit by reducing the friction factor of the formation on the bit and drill string. Since most drilling fluids contains additives (i.e. bentonite, polymers) which help reduce the downhole friction, further lubricants need not to be used unless warranted by difficult and unusual conditions such as sever doglegs or high torque. Unless a bit is well cooled, it overheats and quickly wears out. Fluid circulated around the parts of the bit removes the heat. Oily substances in the drilling fluid can reduce friction in the bit bearings and act as a lubricant between the drill string and the walls of the hole. Oil-emulsion mud and oil base mud are especially helpful in this way..  Transmitting hydraulic horsepower to the bit: The drilling fluid is the medium through which hydraulic horsepower is transmitted to the bit. A viscoelastic drilling fluid, that is a drilling fluid whose viscosity at the bit approaches the viscosity of water, will minimize the friction losses and maximize the available hydraulic horsepower at the bit. Fluid flowing from the bit nozzles exerts a jetting action that keeps the face of the hole and the teeth edge of the bit clear of the cuttings. The horsepower required to move the mud through the remaining system should be minimized in order to maximize horsepower at the bit. The heavier a fluid becomes, the greater the horsepower that is required to move it through the system. This results in less horsepower at the bit and slower penetration rates. Hydraulic energy can be used to maximize the rate of penetration by improving cuttings removal at the bit. It also provides power for mud motors to rotate the bit. Hydraulic energy is measured in terms of hydraulic horsepower..  Cleaning the bottom of the hole: This function of the drilling fluid is essential to achieve the optimum penetration rate with a given bit, weight, rotary speed and hydraulic program. A properly designed hydraulics program should provide an adequate flow rate to create a sufficient cross flow across the bottom of the bit to instantaneously lift the cutting being drilled up. Otherwise, penetration rate will be retarded due to regrinding of the cuttings by the bit. The usual method for cleaning the hole is by circulation of fluids through jet nozzles in the bit. High-velocity streams of fluid blast the bottom of the hole, creating a turbulence that moves the chips from the face of the formation as fast as they are formed.. PetroServices GmbH Training Center. Page 34 of 196.

(35) Basic Mud Logging  Removing cuttings: Removal of cutting from the hole is a vital function of the drilling fluid. This function is primarily dependent on the annular velocity profile and not strictly on the average annular velocity as commonly assumed. The annular velocity profile, in turn will depend on both the average fluid velocity and the viscosity (mainly yield value) of the mud. The yield value can be controlled by drilling fluid additives and should be maintained at the minimum value required for optimum solids removal from the hole. Precise control of the gel strengths of the mud is also important to suspend the cuttings when circulation is stopped. The required yield value and gel strengths will depend on the type of drilling fluid in use and should be adjusted as dictated by the hole conditions in a given drilling area..  Supporting the walls of the well: A drilling fluid with the proper characteristics can support a formation that might otherwise cave in. This type of drilling fluid, or mud, plasters the walls of a well like mortar. Furthermore, the hydrostatic pressure created by the weight of the fluid column in the hole pushes against the plastered wall to support unconsolidated or loose formations that might fall or slough into the hole. Hard rock formations have little tendency to slough and can therefore be drilled with air, gas or water instead of mud. Filter cake, the plaster-like coating formed from mud solids on the walls of a well, has the ability to seal the wellbore and prevent the loss of whole fluid. The force of the hydrostatic pressure squeezes the liquid part of the mud (the filtrate) into the permeable zones (such as sand), and the solid material is left behind as a filter cake..  Controlling formation pressures: The drilling fluid density should be adequate to contain any formation pressures encountered to prevent the influx of formation fluids or gases into the wellbore and provide a safety margin while tripping pipe. However, it must not be so high as to create excessive differential pressures, which will impede drilling rate and may cause lost circulation and differential sticking. Water or mud produces sufficient hydrostatic head to overcome formation pressures usually encountered. The addition of weighting material to mud being circulated in a well can make a mud dense enough to hold back almost any formation pressure. When formation pressures are expected to be high, a high mud weight is needed, so the pits and other equipment should be arranged to handle the heavy mud. A mud weight of 16 to 18 ppg is considered heavy..  Transporting cuttings to the surface: Drilling fluids in circulation moves rock chips, sand, or shale particles out of a well as it moves up the annulus. The drilling fluid velocity in the annulus is usually from 100 to 300 feet per minute (ft/min) in order to keep the hole clean. The solids in mud are separated at the surface by screening, settling, centrifugal action, chemical flocculation, or a combination of methods. Solids brought up by air or gas in air drilling are blown as dust or fine chips to a waste pit. Yield value and gel strengths, which affect the suspension and removal of the drilling solids from the wellbore, also affect the efficiency of the solids removal techniques at the surface. These properties are controlled by the colloid fraction of the drilling fluid and must be sufficient to suspend and remove cuttings from the wellbore, yet low enough to release the cuttings at the surface.. PetroServices GmbH Training Center. Page 35 of 196.

(36) Basic Mud Logging Drilling fluid types: Many types of drilling fluids are used on a day to day basis. Some wells require that different types be used at different parts in the hole, or that some types be used in combination with others. The various types of fluid generally fall into a few broad categories:  Water: Water by itself is pumped to do very specific things in very specific formations.  Water-based mud (WBM): A most basic water-based mud system begins with water, then clays and other chemicals are incorporated into the water to create a homogenous blend resembling something between chocolate milk and malt (depending on viscosity). The clay (called "shale" in its rock form) is usually a combination of native clays that are dissolved into the fluid while drilling, or specific types of clay that are processed and sold as additives for the WBM system. The most common of these is bentonite, frequently referred to in the oilfield as "gel". Gel likely makes reference to the fact that while the fluid is being pumped, it can be very thin and free-flowing (like chocolate milk), though when pumping is stopped, the static fluid builds a "gel" structure that resists flow. When an adequate pumping force is applied to "break the gel", flow resumes and the fluid returns to its previously free-flowing state. Many other chemicals (e.g. potassium formate) are added to a WBM system to achieve various effects, including: viscosity control, shale stability, enhance drilling rate of penetration, cooling and lubricating of equipment.  Oil-based mud (OBM): Oil-based mud can be a mud where the base fluid is a petroleum product such as diesel fuel. Oil-based muds are used for many reasons, some being increased lubricity, enhanced shale inhibition, and greater cleaning abilities with less viscosity. Oil-based muds also withstand greater heat without breaking down. The use of oil-based muds has special considerations. These include cost and environmental considerations.  Synthetic-based fluid (SBM): Synthetic-based fluid is a mud where the base fluid is a synthetic oil. This is most often used on offshore rigs because it has the properties of an oil-based mud, but the toxicity of the fluid fumes are much less than an oil-based fluid. This is important when men work with the fluid in an enclosed space such as an offshore drilling rig.. Mixing drilling mud: Attention should be given to the equipment used to mix drilling mud’s and to the sequence of addition of the mud and any additives. • • • • • • •. If the make up water requires treatment, always treat it prior to addition of the bentonite clay. Use a jet hopper mixer to disperse the bentonite clay. Bentonite clay (Super Gel-X) should be mixed slowly through the jet hopper at a rate of one 50 lb. bag every 10 to 20 minutes. Volume of mud pit should be three times the volume of the proposed hole. Figuring volume of pit length (ft.) x width (ft.) x depth (ft.) x 7.5 = volume (gal). The mud pit should be of such design that the drilling mud, during flow, changes direction and slows, allowing for cuttings to drop out. The addition of viscosifying polymers should be made after the bentonite clay mud is thoroughly mixed in fresh water. Viscosity and density tests should be run on the drilling mud following mixing. Periodic tests should be made during drilling and changes noted. Sand content tests should be run on the mud once drilling starts.. PetroServices GmbH Training Center. Page 36 of 196.

(37) Basic Mud Logging Mud properties terminology: Various properties of the mud are measured as an indication of the performance of the mud in the hole. Tests commonly made are:. 1. Mud weight (density): Mud weight is a density measurement expressed in terms of the weight of a unit volume of the drilling fluid. Ideally, a mud weight as low as the weight of water is desired for achieving optimum penetration rates and for minimizing the chances of loss of circulation. However, in reality, mud weight as high as two and one-half times the weight of water may be necessitated to prevent or control a “well kick” or “hold back” troublesome formations. As a rule, to achieve the optimum penetration rate with safety, the mud weight should be kept at a minimum value that will balance the formation pressures and provide a slight overbalance to insure safety against swabbing the well during connections or trips. As is with other mud properties, the ability to effectively control the mud weight is directly related to the capability of controlling the nature and content of all solids in a drilling fluid. The mud weight may be determined using any instrument that will permit accurate measurement within 1/10 lb/gal or ½ lb/cu. ft. The mud balance is the instrument generally used. Mud weight can be expressed in lb/gal, lb/cu. ft., and psi/1000 ft. of depth or specific gravity (S.G.).. Procedure: 1. Fill the cup with the mud to be weighed. 2. Place the lid on the cup and seat it firmly but slowly with a twisting motion. Be sure some mud runs out of the hole in the cap. 3. With the hole in the cap covered with a finger, wash or wipe all mud from the outside of the cup and arm. 4. Set the knife on the fulcrum and move the sliding weight along the graduated arm until the cup and arm are balanced. 5. Read the density of the mud at the left-hand edge of the sliding weight. 6. Report the result to the nearest scale division in lb/gal, lb/cu ft, S.G., or psi/1000 ft of depth. 7. Wash the mud from the cup immediately after each use. It is essential that all parts of the mud balance be kept clean if accurate results are to be obtained. 8. Refer to Table 1 for conversion data if not available on balance. Calibration: The mud balance should be calibrated frequently with fresh water. Fresh water at 70º F will give a reading of 8.33 lb/gal or 62.3 lbs/cu ft. To adjust the mud balance to the proper reading, add or remove lead shot from end of balance arm or adjust set screw at the end of the balance arm.. PetroServices GmbH Training Center. Page 37 of 196.

(38) Basic Mud Logging 2. Mud viscosity: Qualitatively, viscosity is defined as “the internal resistance of a fluid to flow”; the drilling fluid viscosity can be expressed as either relative or absolute measurements. The relative measurements are the funnel viscosity and the qualitative viscosity. The absolute measurements are the quantitative values of the non-Newtonian characteristics, namely, the plastic viscosity, the yield point and gel strengths..  Funnel viscosity: The Marsh Funnel Viscosity is the ratio of the speed of the mud as it passes through the outlet tube (the Shear Rate) to the amount of force - the weight of the mud itself - that is causing the mud to flow (the Shear Stress). Marsh Funnel Viscosity is reported as the number of seconds required for one quart of mud to flow out of a full Marsh Funnel. Procedures: 1. Collect a fresh mud sample. 2. Hold the funnel erect with a finger over the outlet tube, and pour the mud into the funnel through the screen until the mud level reaches the bottom of the screen (The screen will filter out the larger particles that could clog the outlet tube). 3. Quickly remove the finger from the outlet tube, and at the same time, begin timing the mud outflow. 4. Allow one quart (946 cc) of mud to drain from the Marsh Funnel into a graduated container. 5. Record the number of seconds it takes for the quart of mud to flow out of the funnel, and report this value as the Marsh Funnel Viscosity. Also, record the temperature of the mud sample in degrees F or C. Care of the funnel: Follow these suggestions to care for the Marsh Funnel: 1. Clean and dry the funnel thoroughly after each use. 2. Take special care not to bend or flatten the brass outlet tube at the bottom of the funnel. The Marsh Funnel Viscosity readings are computed using the exact diameter of this outlet and if the outlet is distorted the readings will be inaccurate.. Calibration check: Periodically check the calibration of the Marsh Funnel by measuring the viscosity of fresh water. The funnel is dimensioned so that the outflow of one quart (946 cc) of fresh water at a temperature of 70‘±5‘F (21‘±3‘C) is 26±0.5 seconds. If the Marsh Funnel checks out of calibration, it should be cleaned again, using a pipe cleaner, to make sure that there is nothing obstructing the outlet. If the Marsh Funnel continues to give an incorrect reading for fresh water after cleaning then the outlet tube probably has been bent out of shape and the funnel should be replaced.. PetroServices GmbH Training Center. Page 38 of 196.

(39) Basic Mud Logging  Plastic viscosity: In term of physical relationships, the plastic viscosity is the part of the flow resistance of the fluid caused by mechanical friction within the fluid. This mechanical friction is due to the interaction of solid particles in the mud, the interaction of solid and liquid particles, and the deformation of the liquid particles under a shear stress. The interaction between the solid particles and between the solid and liquid particles will in turn depend on the type and nature of the particles, the number of particles, the size of particles, the shape of particles and the state of particles present in mud. Even though the plastic viscosity cannot be calculated or determined exactly based on a given concentration of solids, the observed value of the plastic viscosity will be a qualitative indication of the solid contents of a drilling fluid. Plastic viscosity is defined as the 600-RPM shear stress reading minus the 300-RPM shear stress reading.. Rotational viscometers.  Yield point: The yield point is physically the measurement of the electrochemical forces within the mud under flowing conditions. These electrochemical forces are due to the charges on the surface of reactive particles, the charges on the sub-micron size particles, and the presence of the electrolytes in water phase. The yield value is the dominant factor that affects the circulating friction losses, the equivalent circulating density, the transition point into turbulent flow, and the carrying capacity of a drilling fluid. Yield point is defined as the 300-RPM shear stress reading minus the plastic viscosity. Yield point is a measure of the attractive forces between active clay particles in the mud under flowing conditions. When the mud is at rest, the solid particles tend to arrange themselves in such a manner that these attractive and repulsive forces are best satisfies. It is also a measure of the hole cleaning capabilities of a mud.. PetroServices GmbH Training Center. Page 39 of 196.

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