Risk-based safety analysis of well integrity operations

Assurance of well integrity is critical and important in all stages of operation of oil and gas reservoirs. In this study, well integrity is modeled during casing and cementing operations. Two different approaches are adapted to model potential failure scenarios. The first approach analyzes failure scenarios using bow-tie model which offers a better visual representation of the logical relationships among the contributing factors through Boolean gates. The second approach takes advantage of Bayesian network, both to model conditional dependencies and to perform probability updating. The analysis identified managed pressure drilling system, logging tool, slurry formulation, casing design, casing handling and running method, surge and swab pressures as critical elements of the well integrity model. A diagnostic analysis on the slurry formulation further identified pilot test(s) and the interpretation of the test(s) as key elements to ensuring integrity of cementing operation. Relevant safety functions and inherent safety principles to improve well integrity operations are also explored.