Experimental Evaluation of a Radial Casing Expansion Surface Casing VentFlow Remediation Technique for Oil and Gas Wells

摘要

Successful operation and decommissioning of oil and gas wells relies on good hydraulic isolation betweenall potential hydrocarbon containing formations,ground water and surface; however,surface casing ventflows(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 operationalloads that the well experiences.Suncor Energy is considering a remediation technique that uses casingexpansion to close a micro-annulus.The tool that embodies this technique applies a radial displacementto the inside of the casing and locks that displacement in place,with the objective of permanently closingthe micro-annulus.This paper describes a full-scale testing evaluation program on specimens designed tomimic the field environment and evaluates the effectiveness of this technology on reducing flow throughmicro-annuli.The experimental program consisted first of designing,building,and conducting tests on specimensthat mimic the casing-cement-formation system.A containment sheath,constructed of fiberglass,wasused to approximate the overall radial stiffness of the caprock formation in Suncor's SAGD wells inWestern Canada.Each specimen was created with a micro-annulus,either between the cement and thecasing or between the cement and the sheath(formation).To evaluate the effectiveness of the remediationtechnique in closing micro-annuli,flow was established through the annulus in the specimen and the toolwas 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 tocompletely close the leak paths.Further,the relationship between the flow rate and the radial expansionof casing from the tool being set was significantly different than hypothesized.Specifically,the flow ratewas expected to decline sharply during early tool set as the micro-annulus was closed and then increaseif further radial expansion caused damage to the cement.Generally,we saw a gradual reduction in flowwith increasing tool set.While the basic behaviours originally hypothesized prior to the study are likely stillpresent,the observed flow characteristics suggest a more complex system response.This study highlighted the importance of considering the full system response in assessing the suitabilityof 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 activationbehaviours,formation stiffness,and cement damage(including pre-existing and tool induced damage).Thisstudy identified how geometric impacts(i.e.,casing non-uniformity)and formation stiffness(i.e.,compliantcaprock formations typical of thermal applications)can influence the effectiveness of casing expansion inreducing SCVF relative to other experiments contained in the literature.The results will support further workto address these uncertainties and optimize the tool design ahead of employing the candidate remediationmitigation technique in the field.