Customization and Implementation of Geomechanics to Successfully Drill High Angle Wells through Ahmadi and Wara Shales, Greater Burgan Field, Kuwait - A Case Study

Abstract

The mature Greater Burgan field is the largest clastic oil reservoir in the world producing from multiple clastic reservoirs. With growing surface area congestion affecting rig moves, current wells are drilled with high deviation often through unstable overburden shales. Well trajectories are getting more complex, resulting in a large increase in hole instability events associated with stuck pipes, loss of bottom hole assemblies often leading to side-tracks, challenging well logging conditions and well completion operations. This paper discusses a holistic and practical geomechanical approach to solve the instability problems, based on understanding the rock failure mechanism of shale, and also discusses the implementation of an integrated solution to drill, log and complete the wells successfully. A thorough geomechanical analysis was done on several wells. Drilling data analytics helped to understand the relationship among formation instability, well trajectory and mud parameters. Lab tests (chemical and mechanical) were performed to determine the chemical and mechanical behaviour of the rock and its interaction with drilling fluid. Anisotropic shale strength tests were targeted to know the rock strength variation with respect to angle of attack. Geomechanical models were prepared and calibrated with observations of drilling problems. Based on integration of models and experiences, effective solutions were devised to implement at well planning as well as drilling stages. A combination of measured and modelled parameters suggested that multiple failure mechanisms are active to induce shale failure including (a) stress induced borehole breakouts, (b) chemoporoelastic interaction of mud and rock fluid and (c) weakening of shale bedding planes and micro fractures. A customized real-time geomechanical monitoring solution was implemented for improved drilling performance and efficient completion of new wells. Specific mud design and mud weights for drilling high angle wells (65-70 deg) were generated and used in real-time while drilling. With the help of LWD and mud logging data, real-time decisions were taken based on well behaviour to drill the wells in a single casing section. Wireline logging and lowering of completion string was completed without any resistance even after the long section of shale was exposed for several days. This entire re-engineering of the process was accepted as a cost-effective and efficient solution that is being recorded as a best practice for implementation in future wells. Integration of diverse disciplines (geomechanical, geochemical, petrophysical and drilling engineering) was successfully implemented to drill a complex well. Real-time geomechanics along with customized drilling fluid and drilling practices enhanced the drilling efficiency. This integrated solution is expected to significantly reduce non-productive time in future upcoming wells with complex well profiles.