Detection Of Casing Failures In Steam Injection Wells At Cold Lake Using Pressure And Rate Data
Authors: Brown Steven J. 
Published: March 2010

A simple system to detect casing failures during the injection phase of a cyclic steam stimulation (CSS) process has been developed for wells at Cold Lake. Although not common, casing failures are a primary concern in a CSS operation as they cause excessive shut-in time and put the integrity of the well at risk. The system, using data normally taken on a daily basis at the well, consists of an injectivity indicator and guidelines/or itsuse.

The indicator is a linear approximation of injectivity, derived theoretically and empirically from Esso's pilot experience. The guidelines have also been derived from pilot experience and theory and include typical injectivity changer due to casingfailures, interwell communication and communication to variousA simple system to detect casing failures during the injection phase of a cyclic steam stimulation (CSS) process has been developed for wells at Cold Lake. Although not common, casing failures are a primary concern in a CSS operation as they cause excessive shut-in time and put the integrity of the well atrisk. The system, using data normally taken on a daily basis a the well, consists of an injectivity indicator and guidelines/or its use.

The indicator is a linear approximation of injectivity, derived theoretically and empirically from Esso's pilot experience. The guidelines have also been derived from pilot experience and theory and include typical injectivity changer due to casing failures, interwell communication and communication to various mobility zones.

Introduction

Cyclic steam stimulation is the primary recovery process used by Esso Resources Canada Limited's operation at Cold Lake, Alberta, to recover bitumen from the Clearwater formation. Due to the high-bitumen viscosity and low initial water saturation, steam stimulation results in parting of the reservoir. The steam generators in operation at Cold Lake produce 80% quality steam at up to 14 MPa and 340 °C. Injection pressures at the wellhead may be as low as 2 MPa and as high as 14 MPa.

Need for Casing Failure Detection

Steaming of wells utilizing the CSS process creates an environment in which casing failures may occur, even though steps have been taken to ensure the casing and cement can withstand the thermal stresses involved with the process.

The use of both L80 casing and thermal cement will withstand the thermal stress, however, overinjection of fluids into the Clearwater formation (430 to 480 mTVD) causes overpressuring and formation movements in this unconsolidated sand. Formation movements will deform the casing, anywhere from slight crimps or inward bulges to complete parting. These deformations are essentially independent of casing strength. By varying steam volumes and steaming patterns the magnitude of the formation movements can be altered. The failures often occur at the perforations or near the top of the Clearwater, both areas where formation movement is likely the greatest.

Uphole casing failures have also occurred, primarily in wells with older casing designs. For example, steam injection into the Colorado Shale can result in failure of adjacent wells due to loss in integrity of the shale. When casing failures occur, losses include the shut-in production and the cost to repair the well. If not repairable, then the well will have to be abandoned.

The detection of casing failures with pressure and rate data is done by monitoring the injeclivity of the well. Failures are identified by a sudden increase in injectivity after some constant period. When communication to water sands and adjacent wells occurs, the injectivity tends to increase at a steady rate. This difference is imp