Wellbore instability analysis for highly fractured carbonate gas reservoir from geomechanics prospective, Saudi Arabia case study

A major challenge facing the oil and gas drilling operations is mitigating the encountered wellbore instability issues. Those can vary from loss circulations up to having stuck pipes or tools that may jeopardize well integrity and potentially lead to total loss of wells and assets. These problematic situations are even much more complicated in fractured reservoir environments where predicting the fracture density is important. Analyzing such problems is critical for companies especially in developing offshore fields where one day lost time is in hundreds of thousands of dollars. The field of rock mechanics emerged to connect those phenomena to reservoir rock properties and stress profiles. Coupling this with an intensive analysis of drilling parameters, logging, core testing and other existing wells data builds a work frame that helps in understanding the reasons behind wellbore failures and providing solutions to them. The field under investigation is a highly geo-pressured offshore gas field. The field development called for drilling vertical and deviated wells. During the field increment sever loss circulation were encountered that resulted in lost drilling times estimated in millions of US dollars with rig cost up $200,000/Day. Other drilling failures includes, stuck drill pipe and difficulties with logging response and log interpretation. The objective of this study is to investigate the wellbore instability during drilling operations as function of rock properties, in-situ earth stress and drilling parameters. Emphasis on the role of natural fractures density will be highlighted and included in modeling inputs as well as characterizing its density across the field. During the course of the study, existing field's and drilled wells available data will be analyzed and a simulation models will be utilized to simulate the stress profiles in the field. Based on the results, the factors behind the instability issues in the field will be identified and recommendations will be made for future wells drilling programs.