Anti-channeling cementing technology for long horizontal sections of shale gas wells

Large-scale hydraulic fracturing combined with horizontal well drilling is the key technology in shale gas development. But poor cementing quality is a crucial bottleneck restricting well completion and reservoir stimulation. In this paper, the shale gas development blocks in the Sichuan Basin were taken as the examples to explore the process and support measures that can be used to keep the mechanical integrity of cement sheath under the effect of hydraulic fracturing. It is indicated that the near-bit three-centralizer drifting BHA used for casing stiffness simulation can decrease the casing running difficulty in the long horizontal section of a shale gas well and increase the time efficiency and safety of casing running; that the flushing efficiency of high-efficiency oil flushing spacer fluid system is higher than 90% from room temperature to 120 °C, so it can guarantee the displacement efficiency of cement slurry to the oil-based drilling fluid and the effective cementing of borehole wall; that the performance of anti-channeling ductile cement slurry used in the cementing of long horizontal sections in this area after it is set is confirmed, with the elastic modulus of set cement being lower than 7 GPa and triaxial strength being higher than 40 MPa, so as to alleviate or avoid the damage to cement sheath in the process of fracturing; and that cementing quality is improved by applying the support technologies, e.g. drilling fluid adjustment, pre-stress cementing and ground high-pressure pumping. During 2015–2016, these cementing technologies were applied in 85 wells in the Sichuan Basin. The average well depth of these wells is 4832 m, the average length of horizontal sections is 1560 m and the quality rate of well cementing is 89.58%. During the waiting-on-cement (WOC) time after well cementing, there is no sustained casing pressure. And gas channeling in the annulus during well drilling, completion and test is improved remarkably. It is concluded that this suite of technologies can guarantee and improve the cementing quality of long horizontal sections in shale gas wells and provides good cementing conditions for shale gas development.