Foamed Cement Mitigates Gas Migration in Shallow Thermal Wells in Alberta

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 214768, “Mitigating Gas Migration Using Foamed Cement on Shallow Thermal Wells in Northeast Alberta,” by Charles Sylvestre, SPE, Sanjel Energy Services; Julio Oliveira, Suncor Energy; and Heyong Jiao, Sanjel Energy Services. The paper has not been peer reviewed. A foamed cement solution was designed and implemented to cement shallow intermediate casing strings in a heavy oil play in northeast Alberta after conventional area-specific cementing solutions could not prevent surface casing vent flows. Foamed cement was pursued as a better alternative technical solution and ultimately led to its successful placement in the field. Significant technical and operational hurdles were overcome to confirm proper well control and ensure that the energized cement could be pumped safely and effectively. MacKay River is Alberta’s shallowest steam-assisted gravity drainage (SAGD) project, with wells typically ranging between 100 m and 150 m true vertical depth (TVD). Wells have been drilled recently at MacKay River with a horizontal length approaching 1000 m and total length exceeding 1500 m measured depth (MD). Wells at MacKay River are drilled using a slant rig because of the extremely shallow depth of the reservoir. The wells feature a three-string casing design with a shallow surface casing, an intermediate casing that runs from surface to the target formation and is landed at 90° inclination, and a horizontal production (or injection) liner hung off the intermediate casing. The intermediate casing is cemented in place and uses premium connections incorporating a metal-to-metal seal to provide a barrier between wellbore fluids and the formations overlying the reservoir. The complete paper discusses a new pad at the MacKay River SAGD operating site. The specific operations discussed are those involving intermediate cementing. One of the most unusual features of the case wells was the discovery of gas trapped under a shallow formation at approximately 80–100 m vertical depth. The pad adjacent to this new pad has been in operation for 17 years. The second obstacle was the hole and casing size, which creates a large annulus. The open hole size was designed at 374.7 mm with the intermediate casing sized at 298.5 mm. This creates an annular gap of 38.1 mm in a gauge hole, but typically these wells require 150% cement excess to achieve cement returns to surface, meaning that, in certain areas of the well, the annulus is much larger. The next challenge presented by the case wells is that they are slanted wells, spudded at an angle of approximately 45° from the surface. The low temperature of these wells also adds to the complexity of preventing gas flow. At such low temperatures, cement sets much slower than in other well types. Finally, the shallow nature of the well, landing at only 113 m vertical depth, does not allow effective hydrostatic pressure control while the cement sets.