Wells in the Montney Formation area, British Columbia, Canada, were designed as monobores and include surface and long lateral production casings. The decision to modify the openhole (OH) completion to a cemented sleeve system presented some concerns. A comprehensive data set from all prior cement operations was compiled and analyzed. This data showed severe gas migration to surface for both an OH completion and cemented lateral well.
Computational fluid dynamics (CFD) and a finite-element simulator were used to evaluate both conventional and foam cement options using actual centralization and caliper log data. The results from this analysis identified a gas-flow potential factor (GFP) was of an order of magnitude where only compressible, foam cement would provide the required properties to achieve competent, long term zonal isolation.
The characteristics of foam cement include a high kinetic energy that assists removing immobile mud trapped on the low side of the casing. Additionally, in this case, using a foamed spacer further improved mud removal from the annulus, resulting in improved displacement efficiency, as observed in the final cement evaluation logs. Filtrate loss and reduced hydrate volume can allow gas migration, giving rise to surface casing vent flow (SCVF) while the cement is curing. Foamed cement helps create a highly compressible cement system that can compensate for these volume decreases and reduce the potential for SCVF. The ductile properties of the set foam cement help mitigate the likelihood of cement debonding and cracks forming during hydraulic fracturing operations, which also helps to reduce the potential for SCVF.