--> Integration Of Drilling Plan With Geomechanical Modeling Efficiently Optimizing Horizontal In-Fill Wells Drilling Performance Through Depleting Reservoir In East Java Basin, Indonesia

AAPG Asia Pacific Region GTW, Pore Pressure & Geomechanics: From Exploration to Abandonment

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Integration Of Drilling Plan With Geomechanical Modeling Efficiently Optimizing Horizontal In-Fill Wells Drilling Performance Through Depleting Reservoir In East Java Basin, Indonesia

Abstract

Reservoir pressure depletion due to production can induces stress redistribution in the depleting reservoirs and surrounding rock. These stresses changes can induce various geomechanical problem such as wellbore instability, sand production, fault instability, and many more. The fracture gradient may decrease, hence safe drilling window which is pressure differences between kick and fracture gradient could be narrower due to depletion. This narrow mud weight window could create problem during drilling in-fill wells especially for multi-stacked sand reservoirs with shale, whereby pore pressure in shale is maintained virgin whilst pore pressure and fracture gradient in the sand are depleting.

These issues will need to be managed by optimizing mud weight program and required good strategy for casing-shoe depths selection to drill the well safely. The level of depletion at which the reduced fracture gradient becomes an operational issue is a function of the geomechanical properties of the reservoir and surrounding rock. For the solution, geomechanical modeling in form of Mechanical Earth Model (MEM), that consist of elastic properties (Young’s modulus and Poisson ratio), rock strength (unconfined compressive strength, friction angle and tensile strength), pore pressure profile, overburden stress and horizontal stresses magnitude with their orientations, is constructed. MEM is subsequently used for wellbore stability analysis in planned in-fill wells and include the depleted reservoir pressure. Based on the result of wellbore stability analysis, optimum mud weight and casing setting depth is estimated to guide drill the well safely.

PETRONAS Carigali Muriah Ltd. (PCML) is drilling in-fill wells in East Java Basin, Kepodang Field, whereby NN sands are depleted with various pressure reduction in each sand. 1D MEMs are constructed based on offset wells data and wellbore stability for planned in-fill wells is subsequently conducted by integrating the offset wells experiences (pore pressure estimation, formation integrity test/leak-off test data, and drilling experiences). Optimum mud weight and casing setting depth strategy is implemented based on geomechanical modeling. The pre-drill model is continuously updated after the first well drilled. From the post-drill analysis conducted for first well drilled, well A, it is found that in 12.25in section there are an indication of well ballooning. During drilling with 600 gpm, losses occurred but when flowrate reduced to below 470 gpm the dynamic losses also reduced but flow back into borehole is detected. Another observation found in well A was pre-drill geomechanics wellbore stability model for 8.5in section suggested fracture gradient is 13.0 ppg. But losses occurred at ECD 12.0 ppg during drilling, which gives indirect indication that the reservoir pressure in NN sands could be further depleted. These wellbore instabilities event and new information of reservoir pressure in NN sands was used to optimize the wellbore stability model for next well to be drilled, well B. Planned mud weight in well B is recommended to be reduced due to higher degree of depletion occurred in NN sands in well B compared to well A. The mud weight is reduced to 11.7-11.8 ppg for 12.25in and 8.5in sections.

PETRONAS Carigali Muriah Ltd. (PCML) has successfully drilled all the planned in-fill wells with minimum wellbore instability issues. Drilling budget expenditure also has been efficiently optimized up to 65% by carefully planning and successfully integrating Geomechanics modeling into Kepodang Field drilling plan and operations.