Cementing Technology Using a Nitrogen-Filled Foamed Cement Slurry for Horizontal Shale Gas Wells in the Eastern Chongqing Area

Normal pressure horizontal shale gas wells in the eastern Chongqing area are prone to leakage during the process of production casing cementing, and often encounter sustained casing pressure (SCP) after staged fracturing. To solve these technical difficulties, this paper studied the cementing technology of mechanical nitrogen-filled foamed cement slurry. Foaming agents and foam stabilizers were selected in the design of low-density foamed cement slurry. Based on the high-pressure gas equation of state, the whole-process pressure balancing of foamed cement slurry and the design of the slurry column structure were performed, and a density calculation model of foamed cement slurry under wellbore pressure was built. In this way, a cementing technology using mechanical nitrogen-filled foamed cement slurry was developed. Specifically, the density of low-density foamed cement slurry ranged from 0.80 to 1.55 kg/L, and the half-life of foam in cement slurry was 33.8 h, with the elastic modulus of foamed cement paste being 4.6 GPa. The residual strain of foamed cement paste under cyclic loading was 0.21%, which demonstrated its good mechanical properties. The whole-process pressure-balancing cementing technology and the slurry column structure design of low-density foamed cement with staged gas injection could meet the requirements of cementing for leakage prevention. When the technology was applied to 20 horizontal shale gas wells in the eastern Chongqing area, no leakage occurred during the construction process, with an excellent rate of cementing quality of 100%, and there was no SCP after fracturing. Research and field applications indicate that the cementing technology using mechanical nitrogen-filled foamed cement slurry can solve the leakage problem of horizontal shale gas wells in the eastern Chongqing area during the production casing cementing, and the foamed cement paste has good elastic deformation, which can prevent SCP after fracturing.