Using Wellbore Stability Analysis to Improve Drilling Performance: Case Study from the Western Desert, Egypt

Abstract

Multiple wellbore stability projects in the Western Desert of Egypt identified a strong sensitivity of the breakout gradient to wellbore inclination and a weak sensitivity to wellbore azimuth, from the Abu Roash to the Alam El Bueib formations. The breakdown gradient shows strong sensitivity to both wellbore inclination and wellbore azimuth. Tensile failures are a problem only in high deviation wells (deviation more than 55-60°) where the breakdown gradient will in general be lower. For highly deviated wells, the occurrence of tensile failure can be reduced by drilling close to the minimum horizontal stress direction.Breakout can be tolerated to some extent, so planning the drilling mud weight to completely eliminate it is not necessary. The extent to which breakout can be tolerated depends on the well deviation, as cuttings become more difficult to evacuate as the well deviation increases.As losses are very common in most of the Western Desert formations, the optimum drilling mud weight should be formulated as a balance between the risks caused by breakout and mud loss.Understanding the main causes of rock failure and applying the recommended failure mitigation measures resulted in successfully drilling four deviated wells in the area. IntroductionThe Western Desert of Egypt is a mature hydrocarbon province. Wells with increasing deviation are being drilled to maximize the hydrocarbon recovery. This leads, however, to a rise in the severity of the borehole instability events. The Western Desert is a tectonically active region where the drilling problems range from mud losses in natural fracture networks or fault zones to time-dependent instability and tight pulls or sticking events. Depleted reservoirs are also encountered, lowering the fracture gradient.Wellbore stability analysis is an important tool to anticipate drilling problems and mitigate failure. We use a systematic approach: first, we analyze drilling reports in offset wells to gather the evidence for borehole failure. Then we develop a geomechanical model and calibrate it until it accurately predicts the observed borehole failures. After model calibration, we can make borehole failure predictions for any wellbore trajectory, regardless of the well deviation or azimuth, and assess the instability risks associated with a particular trajectory. This analysis assures that we choose the optimum drilling mud weight.Applying this process to several wells in one of Gupco's fields in the Western Desert resulted in four successful new wells.

Review of the Leak-off Tests with a Focus on Automation and Digitalization

“…Estimating horizontal stress orientation and magnitude in some operations like wellbore instability analysis, sand control, field developments, and safe drilling operations. Hence, some tests like LOT/XLOT or FIT are conducted for stress measurements [67][68][69][70]. Zhang et.al [71], reviewed the theoretical methods for evaluating in situ stresses and concluded XLOT results are acceptable in estimating horizontal principal stresses, especially in the normal or strike-slip faulting stress regime.…”