WELL CONTROL Precautions in planning HTHP well control
Coordination of planning and site teams critical to fast response
Daniel F. Eby
Wild Well Control
Pre-planning for well control events is not done as a matter of routine. No operator enjoys playing what-if games regarding a blowout. However, as the industry continues to drill more difficult high temperature high pressure (HTHP) wells, the likelihood of well control problems for these types of wells will increase.
The attention level given to HTHP wells in regards to well control can often make a dramatic difference in successfully dealing with well control problems. There are several steps that can be taken to mitigate the effects of well control events on these types of wells.
Design engineering
The first place to start is in the engineering design phase of the well. Drilling engineers should work closely with the geologists and geophysicists to best determine the pressure regime in the prospect. Once the expected pressure profile is generated, fracture gradient determination can be done and the casing points can be chosen.Calculations for the maximum anticipated surface pressure (MASP) during conventional well control, drill stem testing, and production should be considered in the casing design. Kick tolerance calculations should also be made and incorporated where applicable in the well plan.
Minimum allowable casing design safety factors vary with each operator as do the calculations and assumptions used to produce those numbers. Regardless of the method used to ascertain the anticipated surface pressures and safety factors, the casing, wellhead, and BOP equipment should be designed and chosen so that the well can withstand the anticipated pressures without failure. A minimum safety factor of 1.0 for internal yield (burst) is vital in order to protect the lives of the personnel involved in the operations.
In addition to the correct casing design, cementing slurry design and placement practices should be carefully engineered. This is one area that is sometimes lightly considered by drilling engineers and often the duty is delegated to the cementing service company. The project engineer should work closely with the cementing company in order to ensure that the service company is aware of and considers all factors when designing the different cementing jobs.
HTHP awareness
One of the most effective tools in successfully drilling HTHP wells is ensuring that all personnel involved in the project are properly trained and aware of the task at hand. This includes the mud logging company, mud company, cementing company, casing crews, safety specialists, other vendors and all drilling contractor personnel.The well plan should be presented to both the office and the field personnel for these different participants in a pre-spud meeting. All questions and concerns regarding the well can then be addressed and any outstanding issues can be resolved prior to drilling the well.
In addition to the pre-spud meeting, consideration should be given to additional training for the people that will be involved in the project at the well site. In addition to the standard well control training, rig crews, mud loggers, mud engineers, etc. can be trained in the aspects of HTHP drilling that are different than normal operations.
This training should include abnormal pressure detection, well control shut-in procedures, kick handling methods, and other subjects directly related to the project. The training can take different forms. Recently, an operator drilling an HTHP well in the North Sea constructed a one-day HTHP school for the rig personnel that was very effective.
Whatever form the training takes, raising the awareness level of the personnel involved in the project is extremely beneficial and should improve the performance of the people detecting and handling all well control situations that may arise.
BOP equipment
Another factor that can greatly contribute to successfully drilling and testing HTHP wells is thorough BOP and well control equipment inspection and qualification. Many operators are including this step in their drilling HTHP programs as a matter of routine. Once the rig for the project has been chosen, the equipment can be qualified to the desired level. This process can be quite lengthy depending on the condition of the equipment and the process should be considered in the drilling schedule.All components of the wellhead and well control equipment should be considered as candidates for inspection, repair (as necessary) and testing. This includes:
- All wellhead components
- BOP stack
- BOP stack valves
- Accumulator
- Choke and kill lines
- Choke manifold
- Gas buster (or poor boy de-gasser)
- Drill string safety valves
- Standpipe manifold
- High pressure mud lines and system (including cementing system)
- Drill strings
- Drill stem testing surface and subsurface equipment
- Subsea well control equipment, if drilling from a floating vessel.
Wellhead components should meet the product specification level (PSL) specified in the planning stages of the well. All pertinent documentation should be gathered and filed so that it is readily available in the event that it is needed. This also applies to the inspection and repair documentation for the rig and vendor supplied equipment used on the job. Third party inspection personnel should be considered as a documentation coordinator and quality assurance specialists.
Blowout contingency
One of the most proactive steps taken in recent years in HTHP drilling and well control planning is the implementation of a blowout contingency plan (BCP). Most operators have emergency preparedness plans in place in one form or another.
In fact, the governments presiding over most offshore regions in the world require some sort of emergency plan be in place prior to issuing the drilling permit. In addition to the company's standard emergency plan, many operators have a BCP that specifically covers well control events. The BCP may take the form of an area wide (or regional) plan or a one off site specific plan for the HTHP well being drilled. The BCP should include the following:
- Immediate response activities
- Emergency organization
- Well capping procedures
- Well killing procedures
- Specialized well control equipment
- Hazardous fluids, such as H2S and CO2
- Logistics
- Relief wells
When a regional BCP has been written and implemented that addresses the necessary organizational structure, equipment, etc., site specific relief well planning for the HTHP well should be added to enhance the plan.
Relief well planning should include many topics. The relief well design should be as comprehensive as the original well design if not more so. The drilling hazards presented by the blowout well such as subsurface charging as well as those indigenous to the area will need to be considered. A complete relief well plan will contain:
- Relief well target selection
- Surface location selection
- Relief well trajectory design
- Casing point selection and design
- Dynamic kill modeling
- Kill fluid design
- Kill equipment recommendations
- Kill operations recommendations
- Gas dispersion modeling
- Subsea plume modeling (if drilling from a floating vessel)
The dynamic kill models should not only consider a surface blowout, but an underground blowout as well. Reservoir data is critical to proper relief well design so that the blowout model is as accurate as possible. As drilling on the HTHP well progresses, the data obtained should be reviewed and compared to the data used in the relief well plan. If substantial differences exist, the relief well plan should be modified as required in order to keep it valid.
Some operators have dynamic kill modeling capabilities in-house and produce their own relief well plans. Oil company personnel are not likely to be highly experienced in blowout control. As a result, these operators should consult well control specialists form time to time to ensure that they include the latest state-of-the-art principles and methods in their plans.
Pre-planning for HTHP wells can greatly benefit the operator in not only drilling performance but in conventional as well as non- conventional well control operations. The pre-planning should include: detailed well design engineering, HTHP awareness training for all personnel, equipment inspection, and blowout contingency planning
Added attention to these areas during the HTHP project design and execution can pay huge dividends in the form of reduced time and cost for the operator.
Author
Dan Eby is staff engineer for Wild Well Control. He has over 17 years of experience in the oil industry and is involved in all aspects of well control engineering and field execution for WWC. Dan has a BS degree in building construction and a BS in civil engineering from Texas A&M University.
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