Wellbore Stability Management to Avoid Serious Drilling Hazards in High Deviated Well-Application of Real Time Geomechanics

Abstract

A geomechanical evaluation and monitoring programs was conducted in order to reduce non-productive time and drilling complications while drilling in a tectonically stressed area of Kuwait. Offset wells had experienced problems related to the tectonic stresses and associated faults, fractures, complex structures, and anomalous pore pressure. Additional challenges were faced due to complicated and highly deviated well designs where planes of weakness in the formation being drilled and their relative angle with respect to the well path become crucial factors in assessing stability of the borehole. Multiple failure mechanisms such as stress induced wellbore instability, invasion of drilling fluids into weak bedding / micro-fractures and osmotic sensitivity, are found to be the root cause of wellbore instability across reactive shale and other problematic formations especially during drilling of highly deviated wells. To successfully achieve the above objective, it was prudent to be armed with proper assessment and understanding of wellbore stability along with optimizing the most appropriate drilling strategy. Five offset wells were assessed from Geo mechanical point of view in the area in order to simulate the back analysis of the borehole collapse in the unstable zones. The previous wells experience showed a high risk to drill the shales and depleted reservoir formation in one section, causing a high ECD in depleted reservoir which dramatically led to severe losses. The planned well was monitored in real time through the control of the ECD and drilling parameters. Since shales in that section are unstable and tend to be plastically deformed, high mud weights were typically used. Based on the geomechanical inputs of the wellbore stability while drilling, new casing strategy was formulated taking into-account the wellbore stability input, drilling parameters and the mud rheology. The shale section was isolated with separate casing and well was successfully drilled to TD without any drilling complications and minimum Non Productive time. Geomechanical modeling and real-time monitoring allowed the well operator to overcome serious drilling hazards and optimize the drilling practices. This application promises to open the prospect of drilling similar wells without complications and reduced NPT in Kuwait.