A new tool is taking the guesswork out of assessing drilling and completion hazards.

A rapid geomechanics risk analysis tool is providing operators with risk assessments at the earliest stage of well planning. This tool aids in delivering an analysis of area drilling and completion hazards within 5 days to enable initial evaluation of needed casing, mud weight and other risk mitigation programs. Armed with this early knowledge, operators not only can improve well planning but may be able to select a different well trajectory or reschedule the well to optimize their drilling program.
To aid Burlington Resources in planning a 19,000-ft (5,795-m) well in south Louisiana, the tool was used to generate a ranked, weighted and interval-specific summary of risks derived from client field knowledge and offset well analysis within a 5-day span.
This rapid geomechanics tool has been successfully used in more than 60 projects for numerous operators in the Gulf of Mexico region.
Assessment for well planning
The tool is an integrated solution that encompasses a streamlined workflow combining geology, geophysics, formation evaluation and production information to achieve a client-focused understanding of the drilling and completion hazards applying to a specific well site before drilling (Figure 1). The use of this workflow makes it possible to provide the client with an analysis of drilling problems in the vicinity of the planned well and a risk summary on the likelihood and severity of drilling events that may transpire.
The analysis includes the calculation of pore pressure and fracture gradient, enabling the client to select the optimal casing points and mud weight program for the well (Figure 2). Also included are recommendations on the scope of additional work to mitigate remaining risk and lower uncertainty. A key component supporting the short turnaround time is the analytical capability afforded by the Schlumberger Gulf of Mexico pore-pressure cube, in which region-wide pore pressure estimates have been determined by using publicly released velocity data and calibrated to vast amounts of data obtained through formation testing and mud weights taken throughout the Gulf. Enhancing the predictive power available through the cube is the inclusion of client data to yield a customized solution for the specific client well.
Case history 1
The geomechanics group of Schlumberger Data & Consulting Services formed a team with Burlington Resources to evaluate the risks involved in the client's plan to drill a deep near-vertical well in the transition zone along the Louisiana coast.
Burlington's field knowledge combined with detailed offset well analysis improved the understanding of the possible risks regarding the planned well. Early in the study, root cause analysis of drilling problems from the nearby offset well established that downhole hydraulic conditions deteriorated due to reaming and opening the 171/2-in. hole. In addition, wellbore stability (WBS) modeling indicated weak shales. This, coupled with poor wellbore pressure management, had caused large amounts of cavings to enter the borehole. Tight hole conditions and an ensuing stuck-pipe event cost 21 days in non-productive time (NPT) and forced the operator to set 133/8-in. casing.
Using the rapid geomechanics analysis tool, the anticipated risks were gathered in a risk register that summarized the consequence of remaining risks and the scope of mitigation measures (Figure 3). Risks were color-coded by severity and likelihood and represented visually along the planned well bore to indicate the challenging intervals. The study confirmed Burlington's previous findings on the major risks in the area and identified the missing knowledge gaps warranting further risk mitigation. Burlington will capitalize on the study results when drilling the well by applying real-time hydraulic monitoring via annular pressure-while-drilling technology.
Case history 2
A client was planning to drill a vertical well in the southeastern flanks of an extensive diapir in Texas state tracts. Several major faults are associated with the dome and provide reservoir closure, some of the faults having 700-ft to 1,000-ft (214-m to 915-m) throw. Dipping of the beds is significant to the east, which may be varied due to faulting.
Pore pressure in the offset wells analyzed during the rapid geomechanics risk study identified a steep increase in the pore pressure from 10.0 to 14.0 lbm/gal for a 500-ft (152.5-m) interval with a narrow mud weight window (approximately 1-1.5 ppg) at the bottom section (Figure 4). However, review of the drilling reports revealed that the onset of pressure varied by well location. In turn, this variation was explained by the position of the wells in relation to the geologic structure. The wells closer to the diapir (updip) have higher mud weights at shallower depths than those farther from it (downdip).
The analysis concluded that pressure migration in dipping permeable sands would be a serious risk and suggested detailed 3-D mapping and pressure prediction of the sands. The knowledge of pore pressure in dipping sands aided the client in adjusting casing seat depths and defining the optimal mud weight program to avoid kicks as drilling proceeded.
Conclusion
Through its ability to deliver analyses of area drilling and completion hazards within 5 days, the rapid geomechanics risk analysis tool is benefiting drillers by enabling them to evaluate optimal casing design, mud weight programs and other risk-mitigation strategies at the earliest possible stage of well planning. Not only is planning optimized for the anticipated well, but also the early availability of the information may enable the operator to relocate or even change the design of the well where elevated risks have become known.

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