Measures and results of prevention and control on casing deformation and frac-hit in deep shale gas wells in southern Sichuan Basin

Casing deformation and frac-hit pose significant challenges to the development of deep shale gas in southern Sichuan Basin. By analyzing the mechanism and main control factors of casing deformation and frac-hit, two kinds of risk assessment methods were defined, and the overall prevention and control concept and practice were formulated. The results show that initial stress, pore pressure, fault development and large scale fracturing in local block are the main factors leading to the deformation. The development of fracture through well group and uncontrolled fracturing fluid volume are the main factors leading to pressure channeling. Based on this, the risk classification technology of casing deformation and frac-hit is established, and the dual-optimal, dual-control concept and technology are formed. In terms of the prevention and control of casing deformation, the formation of small-diameter bridge plug fracturing, large section combined fracturing, glass beads cementing, single-well staggered and platform straddle fracturing mode, dual-dimension controlled and lift fracturing, hyperbolic diagnosis, etc. Frac-hit prevention and control formed pump sequence optimization mode, physical and chemical temporary plugging and other methods. The above technology achieved casing deformation rate decreased from 50.4% to 25.4%, frac-hit rate decreased from 58.6% to 33.9%, and the average well kilometer EUR reached 0.52–0.7 million square meters, an increase of 7.7% compared with the previous research, with remarkable results.