Advanced Analysis Identifies Greater Efficiency for Testing BOPs in Deep Water
- C. Mark Franklin (BP) | Richard F. Vargo (Halliburton Energy Services Group) | Udaya B. Sathuvalli (Blade Energy Partners) | Michael L. Payne (BP plc)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- December 2005
- Document Type
- Journal Paper
- 238 - 250
- 2005. Society of Petroleum Engineers
- 2 Well Completion, 1.11 Drilling Fluids and Materials, 1.6.1 Drilling Operation Management, 1.14.1 Casing Design, 1.7 Pressure Management, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.6 Drilling Operations, 1.14 Casing and Cementing, 1.10 Drilling Equipment, 5.3.2 Multiphase Flow, 4.2.4 Risers, 2.1.7 Deepwater Completions Design, 5.2.2 Fluid Modeling, Equations of State
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- 507 since 2007
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Pressure testing blowout preventers (BOPs) with synthetic-based mud (SBM)requires lengthy testing times resulting from pressure/volume/temperature (PVT)influences associated with SBM. PVT influences are especially pronounced indeep water and high-pressure test environments.
A project was initiated in an effort to better understand the mechanics thattranspired during BOP testing. The primary objective was to demonstrate thatthe pressure decline was quantified by the fluid-PVT behavior, mechanicalinfluences and thermodynamics of pressurization, and subsequent cool down. Thesecondary objective was to demonstrate that the pressure decline resulting froma leak could be reliably and efficiently detected with high-resolution pressuredata.
It was theorized that the gradual decay of pressure during the shut-in phasewas a result of the heat added to the system during pressurization. To pursuethis investigation, real-time PVT data were gathered at the cementing-unit (CU)suction and discharge while testing the BOP. In addition, pressure/temperature(P/T) gauges were placed in the drillstring—one at the drill floor, one at themidpoint between the drill floor and the BOP, and one above the BOP stack. Thegauges confirmed significant heat up as the system was pressured up for eachtest. The pressure decreased as the system cooled back toward the ambienttemperature. Modeling techniques were developed to understand the systemresponse.
This paper presents salient aspects of data acquisition, datainterpretation, and modeling techniques.Results demonstrate the potentialto significantly impact the industry, with respect to safety, time, and costsfor BOP testing.
The challenges of obtaining valid BOP pressure tests in an efficient mannerhave increased because of greater water depths, deeper drilling horizons, andhigher test pressures. Fig. 1 shows the important components involved intesting a subsea BOP stack. The system is a pressure vessel comprising the testline from the CU and the drillpipe from the surface of the rig to the BOPstack. In this work, the capacity of the pressure vessel is referred to as thetest volume. The valves in the BOP stack are tested in sequence by closing eachvalve and then pumping fluid from the CU into the test volume until a targetpressure is reached (the pumping phase). At the target pressure, pumping stopsand the test volume is closed until a test is deemed valid (the shut in phase).In deepwater wells, the duration of the shut-in phase can be as long as 45minutes when SBMs are used.
Regulations state that a test is valid when the required pressure is heldsteady for 5 minutes.1 Data from a BOP test are typically recorded on a 4 hourcircular-chart recorder, as shown in Fig. 2. Test validation established by thepressure trace on a chart recorder is based on individual judgment. Often, atest must be repeated when visual inspection of the chart-recorder trace deemsit invalid. Frequently, test durations are longer than necessary to ensure avalid test. The chart recorder (patented more than 100 years ago2) is stillused on the majority of the rigs today. However, recent advances in digitaltechnology and the relative ease of data processing with inexpensivepersonal-computer technology create a clear opportunity for improvement in therecording, analysis, and validation of BOP tests.
During a recent BOP test, the reasons for the gradual decay of pressure withtime were examined. Field experience and anecdotal evidence suggest that testdurations are considerably longer with SBM than with water based muds.Discussions with rig personnel and engineers indicate that though "pressuredecay" is recognized as a characteristic deepwater phenomenon, it has not beenrigorously examined. Further discussions imply that the test duration can besignificantly optimized if the physical mechanisms that control the P/Tresponse of the test volume during the different phases of testing areidentified and quantified. As a result of the numerous benefits from areduction of test duration, a project to understand the physics of the BOP-testprocess was initiated.
|File Size||3 MB||Number of Pages||13|
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