Tensile strength of cement to shale interface

Permanent CO2 sequestration relies on avoiding leakage from the reservoir through the caprock. The highest leakage risk resides at the wells penetrating the reservoir, in particular at the boundary between cement sheath and formation. Models quantifying the risk of cement debonding require the cement-caprock interface tensile strength as an input parameter. An experimental method is elaborated to measure tensile strength of composite shale/cement plugs created under stress and temperature conditions similar to downhole well conditions. Tensile failure always occurs at the cement/shale interface and the interface tensile strength is usually significantly lower compared to reservoir rock or cement bulk tensile strength.