During the planning process, the mud engineers employed at the well site should have been made aware and have been trained in the use of the reporting software. The engineering portion of the contract should have stipulated that the operators’ software took precedence over the contractors standard mud report. Having the report generated electronically has many advantages. It will ensure:
• Uniformity
- Standard reporting format for all BU’s
• In-house database storage
- for further more detailed analysis - facilitate trend analysis
- analysis of the relationship between properties and product use
There are many parts to the report, some are not directly related to fluid performance and will not be discussed at this time.
This section will focus on the following parts:
Part 1. Mud Properties Part 2. Rig Operations
Part 3. Engineering Comments Part 4. Daily Product Usage Part 5. Mud Volume Accounting
No single report or item on the report will allow a complete understanding of mud performance.
However, by looking at the relationship between drilling activity, material usage and properties. It is possible to gain a better understanding. At this point, it must be mentioned that no operational staff should make decision based only on reading the report. The contractor’s support staffs’ function is to aid interpretation and comprehension. Nevertheless, the operations engineer should have suffi-cient understanding to enable a grasp on current and proposed activity and allow a fruitful discus-sion with the support staff.
Part 1. Mud Properties
The contract should call for a minimum of one complete set of test results to be reported every eight hours and a complete report to be submitted every 24 hours. The frequency of mud testing is important, as some engineers may elect to do only one set of results when the rig is inactive. This may seem sufficient, but experience has shown that surface contamination and other detrimental events can go undetected for far too long.
As already mentioned, each piece of information read in isolation will have little value. Therefore, the test results should be automatically stored on a database, to facilitate trend analysis.
Trend analysis will be critical in preventing minor shifts in mud values developing into a problem.
Minor shifts in properties can develop very slowly and only after these are seen over a series of reports, will the true magnitude of the problem be seen.
The test results should then be checked to determine if they are within the programmed specifica-tions, stable or in a process of change. The report’s comments section, should provides an expla-nation as to the engineers’ reaction to fluctuation in the fluid state, and if the engineer has needed to alter the properties to meet well bore conditions. This may have entailed moving properties out-side of the agreed range. It must not be assumed that the programmed properties are cast in stone. Assumptions made during the planning phase may no longer prevail.
After the initial reading the properties will either meet expectations or require additional attention.
The following points will help either identify the cause or provide advice on other factors that may be the cause:
Sample Points
If the sample tested has been taken from a different sample point, this could cause a shift in properties and must be stated at the head of each set of properties, if in doubt confirm with the support staff or speak to the mud engineer.
The following procedures are recommended:
Circulating System Analysis
All drilling fluid tests, where the results are entered on the report, must be performed on samples col-lected downstream of the shakers, before the flow enters the active system. The sample should be taken after all the primary solids removal equipment has sieved the drilling fluid. Mud from the suction will also be checked, the information used by the drilling fluid engineer. This data will only be included in the reporting process, if no circulation has occurred during the test period. The exception to this could be the "Drill-In Fluids" which may contain calcium carbonate. These samples should be taken in the possum belly while circulating.
Drilling Fluid samples that leave location should include depth, time of day, sample point (where taken), relevant drilling operation data lagged to the appropriate task being performed (such as ream-ing, drillream-ing, circulating etc.) and a completed set of test results.
Solids Control Analysis
Samples for solids control equipment for under flow and overflow testing should only be taken after the machine has been in operation for >15 minutes. Accompanying paperwork should include machine information; Model #, Scroll type, machine company serial #. Samples taken of the drilling fluid needed prior to entering the solids control equipment should be collected from a 'T. connection' in the line, not from the pit from which the drilling fluid is being taken.
If high-speed shale shaker screen samples are to be taken, care should be taken to gather a repre-sentative sample of the underflow under all screens.
A degree of conformity is important because knowing where the sample have been taken will removes some of the guess work form trying to interpret unusual results.
I. Drilling/Reaming
The amount of rock removed, formations drilled and contaminants encountered while drilling between each set of results should always be read taking into account.
Factors such as:
• Slow Drilling
- Slow ROP’s will mean lower solids removal efficiency. Anything that results in fine solids being introduced in to the mud system will have an impact on the proper-ties.
• Reaming
- Could have the same effect as slow ROP, poor solids removal
• Reactive Formations
- Hydratable and or dispersive clays drilled with WBM will quickly alter properties - Anhydrite will react with WBM as if drilling cement
• Sub-Surface Contaminants
- Cement
- CO2 (Carbonates) - H2S
• Sub-Surface Influx
- Water or brine flow will have an impact on properties II. Solids Control Equipment
• Shale Shakers
- Tears or holes in the shale shaker screens can cause a rapid deterioration in the properties
- Incorrect screen size
- Secondary Equipment
- Poor equipment performance will impact properties III. Surface Contamination
• Water lines in the pit room
• Intermixing with other stored fluids
• Poor mud additive mixing IV. Dehydration and High Temperature
• Bottoms up samples taken after any static aging at higher temperatures can result in rapid changes in properties
Part 2. Rig operations
Sets of test results are not complete without knowing the context in which they relate. As men-tioned slow drilling or reamming can have an effect.
Part 3. Engineering comments
The engineers’ comments are critical and must interpret the numbers reported in to terms all read-ers will undread-erstand. Conditions at the time of testing such as wellbore condition, ongoing treat-ments and many more, will make a huge difference in how we interpret the report. Therefore, it is critical that from the outset the engineer’s comments lead the reader to the key aspects of the report.
If the report has minimal or inadequate comments, the reader is then in fact left to perform the engineering function. The properties are how the engineer will judge whether the fluid is perform-ing its functions. Important functions such as hole cleanperform-ing, will in part be determined by readperform-ing the viscosity properties, in conjunction with other facts, which may or may not be included in the report, can’t be determined by just reading the reported values. The mud engineer must make statements on the report concerning the capacity of the fluid to perform the key functions.
Part 4. Daily Product Usage
Material used each day will have been mixed for additional volume and to adjust mud properties.
To allow the observation of fluid behaviour, the report should explain the distribution of the product mix. In a perfect world, if there were nothing altering the properties, all the materials mixed would be for volume control. However, this is seldom the case, each mud test may provoke treatments of the circulating system. In reading the report it is possible to see how well the fluid and to a lesser degree, how the mud engineers are performing, by looking at the amount of material being used.
For example, if the properties are stable and the materials used to build new volume have been accounted for, there must be an explanation for the use of additional chemicals.
Part 5. Mud Volume Accounting
This is an area of reporting, which can cause the most concern and can create the most problems for the mud engineers. To get an accurate distribution of volume built and lost is an essential area and requires continual attention. On face value, building new volume should be straight forward, but when for instance, water is being added in large quantities, volume measurement can be left to guess work. The report must have accurate accounting if the fluid performance is to be measured.
Volume Building
There must be separation between the gross volume gain, that is when the volume of mud on site is increased and the volume increases, which only applies to the active system.
Fluctuations in the active system volume will need to be carefully controlled, while additional main-tenance volume for dilution and to fill new hole will be an ongoing process. These two must be reported separately.
Dilution
Dilution is an essential tool for managing the drilling fluid. It can be performed either as a specific act, whereby a given volume of mud is added to the active system over a specified time to meet a fluid requirements, such as a reduction in density. It will also occur as part of the continual mainte-nance activity and is this process that is of concern when interpreting the mud report. The contin-ual addition of new volume to the active is the most difficult to appreciate when assessing fluid properties.
It can be assumed that dilution is always occurring when either base liquids or whole mud is being added, but this is not always the case. To interpret the mud properties correctly it must first be determine if the fluid has been diluted and if so, by how much. Therefore, the mud engineer should be assessing each addition for its contribution to the dilution target and reporting accordingly.
Addition of base liquids or whole mud will not always result in dilution:
Example: Base liquids (water, brine, or oil) added that only replaces that lost via evaporation would not contribute to dilution. Evaporation happens all the time and the volume lost must be esti-mated and subtracted from the dilution volume reported. The following note will assist with evapo-ration accounting.
Evaporation Control
Replacement of water to the system due to evaporation should be controlled separately from dilution.
Replacement of this free water will be controlled based on the flow line temperature and the hours of circulation. Water and oil used to replace that evaporated should not be included in the daily calculation of dilution rates but should be reported separately as volume lost to evaporation. These rates of evap-oration can be extremely high and lead to concentration of products and solids.
Determining evaporation rates for Water-Based mud is necessary, so that water is added to the system to prevent dehydration of the fluid. It is recommended that this formula be used for determining evapo-ration rates at the well site to predict the rate at which "Free" water needs to be added to the system.
This volume of water added is to replace the volume lost by evaporation and should not be used when determining product concentrations.
Example: Mud held in storage used to replace fluid lost either down hole or on surface will not have contributed to the dilution and the volume lost must be estimated and subtracted from the dilution volume reported.