Risk assessment of sustained casing pressure in gas wells based on the fuzzy comprehensive evaluation method

The sustained casing pressure (SCP) threatens the wellbore safety significantly. Generally, the effects of factors that cause casing pressure cannot be quantified. Some vague terms are often used to describe the risk degree. Considering the serious SCP situation in XX gas field in the southwest of China, a SCP risk evaluation model was proposed based on the fuzzy comprehensive evaluation method. Three risk indicators (annulus pressure, cementing quality, and formation leakage) were used to describe the SCP risk. The indicators' weight was determined with the application of Delphi method, and the membership matrix was established based on the trapezoidal distribution membership function and the gas field testing data. Then the evaluation model was used to calculate the risk values and risk degrees of 27 SCP wells in XX gas field. Electronic sensors installing and real-time monitoring were recommended to enhance the safety annulus pressure management. The proposed model provides an important technical basis for the production and management of SCP gas wells.