Real-time risk assessment of casing-failure incidents in a whole fracturing process

Abstract

Abstract With the increasing development of hydraulic fracturing technologies, shale gas exploitation is becoming a highly industrial process. Casing-failure incidents which could cause serious leakage of the high-pressure and hazardous chemicals have triggered an intense public discussion in the fracturing industry. Quantitative risk analysis (QRA) is a common technique used to study the carrying capacity of a casing. However, this technique tends to only show static risk state after the casing has been run down to the formation, but is not sufficient to monitor its real-time failure risk during the whole fracturing process. Therefore, a matrix-based risk assessment method is proposed to improve the conventional QRA by using stress-strength interference theory and value function modelling to calculate the static and dynamic failure probabilities of casings, respectively, over a period of multi-stage sand fracturing. Further studies are developed to integrate these two probabilities with the application of a design matrix, particularly for the quantitative analysis and assessment of casing failures. The visual risk graphs are also provided to show the failure risk states and levels for the casings in real time. The assessment procedures can clearly delineate the operation characteristics of shale gas fracturing − high pressure, large displacement, and sand erosion. To illustrate the validity of the methodology, a production casing of a gas well at one fracturing stage is chosen as a test case. Results show that the real-time risk is more accurate and practical, as well as improving the assessment effectiveness of casing-failure incidents during a whole fracturing period.