BOTTOM HOLE ASSEMBLIES General

Guidelines in this section address the design, care, and makeup of bottom hole assemblies for drilling operations to meet the following objectives:

• Control or Induce Changes in Hole Deviation

• Improve Bit Performance

• Provide Weight on Bit

• Ensure a Full Gauge Hole

• Reduce the Susceptibility to Differential Sticking and/or Key Seating

• Reduce Downhole Vibration

• Prevent/Reduce BHA Problems Such as Wash-outs and Twist-offs BHA Operational Guidelines

1. Three musts for good drill collar performance are:

• Must properly lubricate shoulders and threads

• Must use proper torque - Must be measured

• Must immediately repair minor damage

2. Never make up drill collars or BHA components by reversing the rotary table. Tighten each connection separately. Do not double up to save time.

3. When breaking out drill collars, rotate slowly with a slight upward pull on the blocks. Do not allow threads to jump after the collar is backed out.

4. To avoid galling, a good rig practice is to "walk out" the drill collar joint using chain tongs.

5. Change the stand breaks on the BHA/drill collars on every trip.

6. Optimize jar placement by running jars near most likely stuck point.

7. Keep an accurate drawing of all BHA components including the dimension of each component (OD's, ID's, lengths, serial numbers, etc.). The dimensions should be measured in such a way as to contribute toward successful fishing. Outside diameter dimensions should be taken with a caliper that will just slip over the body by its own weight.

8. Gauging the bit after makeup will ensure that it was not pinched by the bit breaker. Refer to Section 5 (Bit Classification and Hydraulics) for gauging guidance.

DRILLING OPERATIONS

DRILLING OPERATIONS MANUAL - JACK-UP/PLATFORM/BARGE RIG DRILLING 15 of 20 First Edition - May, 2003

9. Maintain stabilizer blade OD, according to the BHA programmed design, by gauging them every trip and replacing as needed. It is preferable to not change more than one stabilizer per trip. Follow the gauging guidelines given in the bit section.

10. Lift sub pins should be cleaned, inspected, and lubricated on each trip. If these pins have been damaged and go unnoticed, they will eventually damage all of the drill collar boxes.

BHA Design

The bottom hole assembly that is to be used in each hole section will be specified in the pertinent drilling procedure. The following considerations should be included when performing a BHA design:

1. HeviWate drill pipe run between the drill collars and drill pipe provides a transition zone as well as additional available string weight. In deeper wells with increasing angle, minimizing HWDP to assist in optimizing drilling hydraulics is a common practice.

2. Ensure that crossovers from large diameter drill collars to smaller drill collars or drill pipe do not exceed a 2" reduction in size, or that the stiffness ratio does not exceed 5.5 for a non-critical well or 3.5 for a non-critical well.

3. The acceptable drill collar and BHA tools bending strength ratio is 2.25 to 3.20.

4. These bending strength ratios may not be possible with small drill collar sizes such as 4 3/4 inch drill collars with 3 1/2 IF (NC 38) connections. Experience has shown that rotary shoulder connection failures have rarely occurred using 4 3/4 inch drill collars even with BSRs below 2.0.

5. Select components of the BHA considering lost circulation material requirements and potential for drill string sticking and subsequent fishing operations (nozzles, motors, MWDs, etc. may plug when pumping LCM).

6. Ensure that all BHA connections have boreback stress relief box connections and stress relief grooves on pins.

7. Spiral drill collars are preferred to minimize differential sticking potential.

8. Straight welded blade stabilizers minimize swabbing in gumbo sections. Stabilizers with a longer contact area increase wall support area in soft formations. Stabilizers with a shorter contact area are preferable in hard formations. Consider use of spiral, integral blade stabilizers with adequate bypass area for high angle, directional well hole cleaning.

Directional Drilling BHAs

These guidelines are not intended to be policy or inflexible standards but should serve as a foundation on which to base decisions for well specific designs.

From about 1950 to 1980, drill pipe and HeviWate drill pipe were never run in compression for fear of fatigue failures as a result of buckling. However, inclination of a wellbore was seldom taken into account in calculating the required drill collar weight. As a result most operators did not add collars

DRILLING OPERATIONS

DRILLING OPERATIONS MANUAL - JACK-UP/PLATFORM/BARGE RIG DRILLING 16 of 20 First Edition - May, 2003

as hole angle increased which undoubtedly caused drill pipe to be run in compression. Fatigue failures expected for drill pipe run in compression did not occur.

Industry has determined that drill pipe can carry high compressive loads in high angle wells without buckling and fatigue failures. Buckling does lead to accelerated fatigue damage and tool joint wear which can be tolerated for short periods of time especially if it would save a trip or reduce the chance of a differentially stuck drill string.

The basis for these conclusions is that a drill string laying on the low side of an inclined hole is very resistant to buckling since the hole supports and constrains the pipe throughout its length. An important benefit of running drill pipe in compression is that the length of HeviWate and drill collars can be reduced and hydraulics, hole cleaning, and ROP can be improved.

FORCAL permits drill string design based on allowable drill pipe compression for deviated or straight wellbores. ROB predicts rates of build or drop for rotary bottom hole assemblies.

Placement of stabilizers on the bottom of a BHA for directional control can be analyzed as well as how drill collars will bend between stabilizers. Directional service companies can provide similar drill pipe design software. Be sure to note the limitations of the particular software being used and check this against the situation being analyzed (e.g. FORCAL needs modified input when modelling casing running because it is based on string theory).

The new BHA design methods which take advantage of the reduced BHA buckling tendency in directional wells have been used since the early 1980s with outstanding results. The short drill collar lengths required (frequently just MWD/LWD equipment for GOM operations) resulted in reduced torque and drag and reduced frequency of differentially stuck BHAs. The amount of drill pipe, HeviWate drill pipe, and drill collars run in compression is well specific and depends on hole size, mud weight, well angle, desired WOB, and torque and drag constraints. All drilling operations should take advantage of design methods which can minimize problems with torque and drag and stuck BHAs.

When differential pressure exceeds about 1,500 psi, take special care to avoid differentially sticking the drill string. Implement special procedures such as making rotating connections, controlling mud fluid loss and mud cake quality, ensuring effective hole cleaning (i.e., limiting cuttings dune height, etc.), and pumping out of hole on rigs with a top drive system. For differential overbalance pressure greater than 2,500 psi consider use of the high overbalance, "Seal-While-Drilling" technique.

For wells between 15-35 degrees of angle, apply the following general BHA guidelines. For wells with >45 degrees of angle special drilling practices may be required.

1. Minimize the number of drill collars and run the maximum amount of drill pipe and HeviWate drill pipe in compression as indicated by the FORCAL program. In most cases only non-mag collars are required in addition to MWD/LWD collars based on well angle, hole size, desired weight on bit, well angle, mud weight, and torque and drag constraints.

2. Do not run more than one unsupported drill collar above the top stabilizer in directional wells.

This can also be eliminated if a non-mag spacer is not required, or if non-mag HWDP is available to be run in place of the non-mag collar. At high angles, additional DC's create a very high bending stress in the top stabilizer connection. They also create the potential for stuck pipe if they sag to contact the wall.

DRILLING OPERATIONS

DRILLING OPERATIONS MANUAL - JACK-UP/PLATFORM/BARGE RIG DRILLING 17 of 20 First Edition - May, 2003

3. The computer program ROB in conjunction with the directional service company software/experience should be used to design stabilizer placement for the BHA. In most area, particularly in areas where differential sticking is a concern, stabilizers should be placed every 60 feet.

4. The directional drilling contractor should provide recommended BHAs for evaluation by the Drilling Engineer.

5. Keep up with differential pressure between the mud weight and pore pressure. Take special precautions to prevent stuck drill strings anytime differential pressures exceed about 1,500 psi regardless of the type formation drilled.

6. In harder formations, roller reamers are sometimes used in lieu of stabilizers. Roller reamers are often used when significant amounts of reaming is anticipated or rotary torque reductions are desired. Non-rotating drill pipe protectors or sleeves should be considered when torque reduction is desired.

7. For steerable PDM drilling assemblies, optimize mud motor and LWD tool configuration to anticipated well conditions including: drilling fluid type, flowrate, downhole temperature, anticipated time between trips, bit type, and drilling WOB and torque requirements. For GOM Directional wells use high performance, extended power section PDMs whenever possible.

FORCAL V.5.02 software estimates the torque and drag on a tubular given the wellbore geometry, tubular configuration, direction of movement, and coefficient of friction. The movement can be axial, rotational, or combined. Two coefficients of friction may be used, one for cased portions of the well and the other for the open hole section. Tripping of tubulars into and out of the wellbore can be modelled. Given the measured torque or hookload, FORCAL can calculate the coefficient of friction.

ROB V.5.01 software predicts the build/drop and walk performance of rotary and motor assembly BHAs. The user can perform sensitivity analysis to predict the effects of various parameters on BHA performance. Geology effects such as bedding planes can also be included and a calibration module allows the user to take advantage of local experience. ROB performs drill ahead and well extend calculations along with 2-D and 3-D well planning.

POWERPLAN V.3.8 is also utilized and has the capabilities of prediction both torque/drag and build/drop and walk of different BHA's.

Torque and drag surveillance should be monitored for all protective and production holes in excess of 40° with greater than 1500' MD of openhole. An example is included in Section 4 – Appendix VIII.