PRODUCTION PROBLEMS IN THE STEAM-STIMULATED SHALEY OIL SANDS OF THE COLD LAKE RESERVOIR - CAUSE AND POSSIBLE SOLUTIONS

The highly viscous bitumen from the Cold Lake reservoir in Alberta is produced by the Cyclic Steam Stimulation (CSS) process. The clean oil sands of the Cold Lake reservoir generally produce well, but the shale y oil sands with imbedded clasts have experienced lower bitumen produc tion and lower steam injectivity. This paper presents laboratory and f ield data that support the hypothesis that the minerals in the clasts play a role in the production problems of the shaley oil sands. Labora tory tests reveal that clasts in the shaley oil sands have an abundanc e of carbonate minerals such as siderite (iron carbonate) and aluminos ilicate minerals such as kaolinite and feldspar. Laboratory studies un der steam stimulation conditions show that the mineral reactions betwe en carbonates and aluminosilicates can generate formation damaging pro ducts such as swelling clay and carbon dioxide. Swelling day can damag e the formation by plugging the pore throats, whereas carbon dioxide c an lead to near-wellbore scaling. Calcium carbonate scales have been o bserved in downhole pumps and liners in Cold Lake wells. The field bit umen production appears to be inversely correlated with the carbonate content of the clasts. The field bitumen production is also inversely correlated with the amount of carbon dioxide generated in the laborato ry by hydrothermal reactions of clasts. The paper describes the applic ation of portable X-ray fluorescence (XRF) and near-infrared instrumen ts for rapid, nondestructive identification of reactive minerals in co res, and of photoelectric absorption (Pe) logs for identifying shaley oil sands with reactive minerals. It proposes diagnostic tests to iden tify the extent and type of damage in a producing well. Finally, it di scusses several potential methods for formation damage remediation and prevention.