Improving Drilling Efficiency Through Wellbore Stability Analysis in the Gulf of Suez, Egypt

Abstract

An increasing number of deviated wells are being drilled to maximize production and hydrocarbon recovery in the mature reservoirs of the Gulf of Suez (GoS). Successfully drilling a high-angle well in a tectonically disturbed and structurally complex area like the GoS is very challenging, especially in depleted reservoirs. Selecting the optimal mud weight is absolutely essential. Stress orientation and magnitude also have a major impact on wellbore stability.The region poses significant drilling challenges that vary widely from reactive shale and salt creep to stress-related instability. From the findings of multiple wellbore stability projects we conducted in the GoS, we review the dominant mechanisms of wellbore instability in the GoS. We provide a summary of the failure mitigation measures and an overview of stress magnitude and orientation in the region, demonstrating how it impacts the knowledge of the most stable drilling direction.Understanding the main causes of rock failure in the GoS resulted in improved drilling efficiency and reduced drilling costs. We show an example, where a new, nearly horizontal (86º) well was successfully drilled through the Asl formation with less than half a day of non productive time during the entire drilling process.We conclude that acquisition of new, high-quality data would considerably reduce the uncertainty surrounding drilling complex wells in the area and reduce their cost. IntroductionThe Gulf of Suez (GoS) is a mature hydrocarbon region of Egypt. Most of the wells were drilled several decades ago, but, to optimize the hydrocarbon recovery, operators are now drilling increasingly deviated wells. This has led to a rise in the severity of borehole instability events, adding to the complexity of drilling in the area. In this tectonically active area, numerous drilling problems are present. They range from salt creep to mud losses in natural fracture networks or subseismic fault zones, without mentioning borehole failure linked to formation/fluid interactions. Highly depleted reservoirs are encountered, with sometimes a high uncertainty in the current pore pressure, leading to high uncertainty on the fracture gradient or the mud loss gradient.The available data is, however, usually scarce because most of the fields were developed a long time ago. Essential data like sonic compressional and shear logs can be missing. Mechanical properties from core are rarely available to calibrate the rock mechanical properties. Little direct information is available about stress magnitudes, as leakoff tests (LOT), extended LOT (XLOT), and hydraulic fracturing are rarely conducted.Wellbore stability analysis can, however, deliver crucial information to mitigate failure in complex new well trajectories. A systematic approach in analysing the causes of borehole instability is necessary to forecast the risks associated with drilling new wells and to recommend mitigation measures. First, the evidence for formation and borehole failure needs to be gathered and analyzed from drilling reports. Th...