Modeling the effect of operational activity on wellbore integrity and wellbore leakage in British Columbia

Abstract

Wellbore leakage, which indicates a failure to provide hydraulic isolation downhole, is an issue facing many wells currently in production in BC. Wellbore leakage is a complex issue that is yet to be fully understood. In the work presented here, we use a previously developed stochastic model of wellbore leakage calibrated to British Columbia data, to investigate the effect of a number of operational factors on wellbore leakage. These include the height of the cement column in the annulus, the intersection of an over-pressured hydrocarbon bearing formation (above the target zone), and the use of squeeze cementing in remedial operations. These effects on leakage have not been previously investigated and our results show that each operational effect can be significant, and why. This suggests that stochastic-based models that capture the variability of the well integrity can be used to support the development of risk-based plug and abandonment (P&A) practices. We repeatedly came to the conclusion that reducing wellbore leakage is often localized, requiring an impermeable barrier be placed across the cap rock. Heterogeneity of the microannulus thickness, both azimuthally and along the well axis, can have surprising effects on the sensitivity of leakage behavior in individual wells and consequently must be accounted for in operational design.