During steam-based-oil-recovery processes (e.g., cyclic steam stimulation and steam-assisted gravity drainage), heat is transmitted from wellbore and reservoir to surrounding formations. The thermally induced deformation in shale can affect wellbore integrity and caprock integrity. In this paper, a compositional thermal strain model was proposed to quantify the thermally induced deformation in shallowly buried shale. The fabric of shale was examined and considered in the model. Thermally induced deformation in shale is contributed by the thermal deformation of shale-solid minerals, dehydration in clay, and thermal plastic strain (grain or particle rearrangement) in shale. Under drained heating, shale can contract or expand depending on its mineralogy, composition, structure, and the imposed temperature. The proposed thermal strain model was validated against the laboratory-test result of a shale sample retrieved from a heavy-oil field in the western Canada sedimentary basin.

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