Reduction of Surface Casing Vent Leaks In Viking/Kinsella, Alberta Using Improved Drilling And Cementing Techniques
Authors: Dousett J. , Akit S.G. , MacDonald R.J. 
Published: March 2010

Abstract
Surface casing vent leaks (SCVLs), subsequent to production casing cementation, became a serious concern in the Viking/Kinsella area. The gas sand formations responsible for the SCVLs were relatively shallow, low temperature, and overpressured. Drilling angled wells from pad locations increased the possibilities of SCVLs due to the difficulty in obtaining a good primary cement job. Conventional drilling and cementing practices did not prove effective in reliably preventing environmental liabilities were incurred.
PanCanadian Petroleum Ltd. Has implemented a number of drilling and cementing "good practices" 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.

Introduction
The main objective of a successful primary 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.

Background
The Viking/Kinsella field is located 20 km 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 defined 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 (Figure 1). PanCanadian set a goal to eliminate all SCVLs in an effort to reduce well lifecycle cost in the area.
PanCanadian utilizes slant well pad drilling in the Viking/Kinsella area to reduce:Capital costs when compared to directional drillingOperating costs; maintain fewer leases and facilitiesWell production operating costsEnvironmental impact by minimizing surface land requirements
A typical well configuration consists of:
Equations (available in full paper)
The operational issues that were addressed in the drilling and cementing of the slant wells in the Viking/Kinsella are:Complete removal of drilled solids from hole,Optimal casing centralization, andOptimal slurry design

Mechanical Considerations
Numerous cementing techniques have been considered throughout the industry to combat SVCLs, all with limited success. They include:Applying additional pump pressure from surface to compensate for hydrostatic losses due to slurry gelation,Placing a fast setting cement at surface and "pancake" squeezing a slower setting slurry into the gas zone, orInflating an external casing packer at the surface casing shoe to provide a mechanical barrier to gas flow.