X-ray tomography (CT scanning) has been used to monitor, in real time, the damage produced by chemical interaction between drilling fluid and Pierre shale in a model wellbore geometry, under downhole stress conditions. This shale is moderately anisotropic, and the experiments examine the effect of the angle between bedding and wellbore. The swollen zone around the wellbore becomes increasingly asymmetric as the angle between bedding plane normal and wellbore axis increases. Swelling and strength tests on the shale at different orientations are described, and the results related to the damage seen in the wellbore experiments.

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