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Well Integrity Analysis Under Imperfect Cementing Conditions in Supercritical Well
Mohmad Mohsin THAKUR, Meng MENG
[Los Alamos National Laboratory, USA]
Super-hot conditions, that include temperatures greater than 375℃, are projected to greatly enhance the power production from geothermal energy. An important component of a geothermal well includes a cement sheath whose integrity is critical for wellbore stability. However, at present thermo-mechanical modeling of geothermal wells typically considers cement as a homogeneous material, with perfect bonding, and symmetrically positioned between casing and formation. The evidence from laboratory experiments and field operations suggests that wellbore cement may exhibit defects such as channels and voids caused by drilling mud fluid, weak cement interfaces with enhanced porosity caused by a wall effect known as interfacial transition zone, and casing standoff caused by improper centralization affecting the overall integrity of the well. These defects in the cement may act as local stress concentrators upon thermal fluctuations, which may initially cause local failure and then propagate globally in non-ideal directions over repeated loading's. Through 2D and 3D simulations, we systemically model defects in cement such as porosity changes, cracks, large voids, and casing standoff in wellbores subjected to thermal fluctuations representative of superhot conditions. We consider two types of wellbore cements with distinct elastic, plastic, and thermal properties. Our work incorporates temperature dependent mechanical properties of casing, cement, and rock. We analyze failure modes such as damage initiation and propagation in wellbore cements subjected to super-hot geothermal environments, emphasizing the role of cement defects in compromising wellbore integrity.
Topic: Modeling