Experimental investigation of the cementation and tensile properties of cement to formation interface considering surface irregularity and drilling mud residue

Abstract Cement sheath is an annular structure situated between casing and formation, which designed to seal the formation reinforce borehole. However, owing surface irregularity drilling mud residue, interface cement one of weakest parts for fluid leakage causing well integrity issues, would also affect reliability bond logs. To evaluate cementation state tensile properties cement-formation interface, rock-cement composite disc specimens are prepared, considering key factors such as lithology, irregularity, treatment oil-based contamination, flushing washing. Flushing efficiency contaminated rock surface, characteristic, referenced strength, fracture morphology acquired analysed comparatively. Results show that (1) efficiencies shale sandstone 74.1 ~ 61.9% 52.4 28.4%, respectively, decreasing with increase in irregularity. (2) The gradually becomes poorly cemented cleanliness increasing. (3) Under condition there exists a transitional area at where microcracks pores developed. (4) With influence strengths shale-cement sandstone-cement interfaces drop from 2.716 0.586 MPa 2.840 0.007 MPa, respectively. effects underground temperature pressure environment not particularly considered this study be investigated systematically future research.