Experimental Evaluation of a Radial Casing Expansion Surface Casing Vent Flow Remediation Technique for Oil and Gas Wells
Authors: Chartier Mark , Graham John 
Published: October 2020

Successful operation and decommissioning of oil and gas wells relies on good hydraulic isolation between all potential hydrocarbon containing formations, ground water and surface; however, surface casing vent flows (SCVF) and gas migration (GM) are common in some areas. Some SCVF can be attributed to a micro-annulus, the source and character of which can vary depending on the cementing program and the operational loads that the well experiences. Suncor Energy is considering a remediation technique that uses casing expansion to close a micro-annulus. The tool that embodies this technique applies a radial displacement to the inside of the casing and locks that displacement in place, with the objective of permanently closing the micro-annulus. This paper describes a full-scale testing evaluation program on specimens designed to mimic the field environment and evaluates the effectiveness of this technology on reducing flow through micro-annuli.

The experimental program consisted first of designing, building, and conducting tests on specimens that mimic the casing-cement-formation system. A containment sheath, constructed of fiberglass, was used to approximate the overall radial stiffness of the caprock formation in Suncor’s SAGD wells in Western Canada. Each specimen was created with a micro-annulus, either between the cement and the casing or between the cement and the sheath (formation). To evaluate the effectiveness of the remediation technique in closing micro-annuli, flow was established through the annulus in the specimen and the tool was incrementally activated inside the casing while the flow rate was monitored.

Test results showed tool activation reduced annular flow between 25% and 70%, but was unable to completely close the leak paths. Further, the relationship between the flow rate and the radial expansion of casing from the tool being set was significantly different than hypothesized. Specifically, the flow rate was expected to decline sharply during early tool set as the micro-annulus was closed and then increase if further radial expansion caused damage to the cement. Generally, we saw a gradual reduction in flow with increasing tool set. While the basic behaviours originally hypothesized prior to the study are likely still present, the observed flow characteristics suggest a more complex system response.

This study highlighted the importance of considering the full system response in assessing the suitability of micro-annulus remediation techniques that rely on casing expansion. Results indicate that flow through a cement sheath is a complex function of initial casing and cement geometry, tool geometry and activation behaviours, formation stiffness, and cement damage (including pre-existing and tool induced damage). This study identified how geometric impacts (i.e., casing non-uniformity) and formation stiffness (i.e., compliant caprock formations typical of thermal applications) can influence the effectiveness of casing expansion in reducing SCVF relative to other experiments contained in the literature. The results will support further work to address these uncertainties and optimize the tool design ahead of employing the candidate remediation mitigation technique in the field.