Real-Time Cement Expansion/Shrinkage Testing Under Downhole Conditions for Enhanced Annular Isolation

Abstract

Abstract Ongoing problems with sustained annular gas pressure on producing wells wordwide is a prime indicator that more work is needed in understanding how cement system design can impact long-term annular isolation. One important area is the relative expansion or shrinkage of cement systems as they hydrate in the annulus of a well. Most Portland cement systems undergo chemical and bulk shrinkage as they set. A number of chemical materials have been developed that can be added to cementing systems to overcome this shrinkage, and in some cases, even impart a degree of expansion. However, the process whereby the degree of shrinkage or expansion is measured has almost universally been some type of a single point test, performed at ambient conditions. This is typically the case even if the cement sample was first hydrated under downhole conditions. The authors detail new methodology and test equipment that allows for the tracking of cement shrinkage and/or expansion real-time, under downhole conditions of pressure and temperature. The system allows for the application of curing pressures in either an aqueous or non-aqueous environment. Data acquisition is totally computerized and can be maintained for whatever time interval is required, without exposing the hydrating cement to surface conditions. With this new technology, the authors will detail how cement expansion and shrinkage can be significantly different under downhole conditions of pressure and temperature than when measured at ambient conditions. It has also been observed by the authors that cement expansion or shrinkage is a dynamic process that may take many hours or even days before any significant degree of volumetric stability is achieved. Finally, a successful field application of the new testing methodology will be presented as validation for the transfer of this new technology from the laboratory to the real world of oil and gas well cementing.