The high frequency of surface casing vent leaks (SCVLs), subsequent to production casing cement. have become a serious concern to operators drilling in east central Alberta.
The gas sand formations responsible for the SCVLs are relatively shallow, low temperature, and over pressured. Drilling angled wells from pad locations increases the possibilities of SCVLs due to the difficulty in obtaining a good primary cement job. Conventional drilling and cementing practices have not proven effective in reliably preventing the gas flow frequency. As a result long term economic and environmental liabilities are incurred; remedial efforts to correct SCVLs are time consuming expensive and often ineffective.
PanCanadian Petroleum Ltd. has recently implemented a number of drilling and cementing "good practices" in all effort to reduce SCVL incidents. The changes in drilling and cementing practices and materials have resulted in a significant reduction in the number and severity of SCVLs. This paper details the combinations and results of the approaches used.
The primary objective of a successful cementing operation is the complete displacement of drilling fluids and solids from the drilled hole/casing annulus with a competent cement slurry designed for area specific concerns. Industry research and experience has shown that even a properly designed cement slurry cannot provide an effective hydraulic seal if contaminated with drilling fluids or solids, or if a channel through the cement exists. Drilling practices have an impact on the quality of the wellbore to be cemented, as well.
This paper addresses the changes in drilling practices and cement design established to eliminate surface casing vent leaks (SCVLs) at the PanCanadian Viking/Kinsella development project.
The Viking/Kinsella field is located 20 kilometers northeast of Viking, Alberta, in TWP 47 RGE 9 W4M. PanCanadian's wells in this field historically suffer from poor zonal isolation and high frequency of SCVLs. A SCVL is defmed as any measurable flow or pressure build up of gas, water or hydrocarbon liquid on a vent on the surface casing bowl.1 This paper specifically refers to SCVLs from gas sources. The source formations in this area are the Viking and Colony formations (Figure 1). PanCanadian set a goal eliminate all SCVLs in an effort to reduce well lifecycle cost in the area.
