Research and Application of Casing-in-casing (CiC) Cementing Technology for Shale Gas Refractured Well

Abstract There is a huge deposit of shale gas resource in the whole world. Shale gas is one of the cleanest energies, with which the carbon discharge after burned is almost a half of that by coal or petroleum. However, the production of shale gas well decrease rapidly and refracturing is an advanced technology to improve the final recovery rate of shale gas well effectively. The CiC (casing-in-casing) cementing is a key technology to provide reliable wellbore support for shale gas well refracturing. By integration of the core technologies including wellbore recovering treatments, perforation plugging technique, carbon fiber patch centralizer and CiC cement slurry system, the CiC cementing technology successfully applied on-site in 9 shale gas refractured wells. The pressure bearing capacity of perforation plugging consolidated caterial can reach to 15.00∼25.00 MPa; The adhesion of carbon fiber patch centralizer is between 80.00∼100.00 kN; The fluidity of cement slurry can reach to be higher than 250.00 mm; The compressive strength is between 18.00∼22.00 MPa with 48 hours curing; With 28 days ambient curing, the compressive strength could reach to 44.70∼48.60 MPa, which effectively improve the anti-damage ability of the thin casing-in-casing cement sheath, ensure the high sealing performance of cement for repeated fracturing. Test production after refracturing achieved 142,600 m 3 /D with a recovery rate of 78.10%, which indicates CiC technology could actually improve the ultimate recovery rate of shale gas depleted well. This study on casing-in-casing (CiC) cementing technology for shale gas refractured well can provide a research foundation for the redevelopment and ultimate recovery rate improvement of clean fossil energy in the world.