页岩气长水平井段防气窜固井技术

页岩气开发的核心技术为水平井配合大型水力压裂,而固井质量不佳已成为页岩气完井和实施储层改造的主要瓶颈问题。为此,以四川盆地页岩气开发区块为例,探索了水力压裂作用下保持水泥环力学完整性的方法及其配套工艺技术措施。研究结果表明:(1)采用模拟套管刚度的近钻头三扶正器通井钻具组合,可以降低长水平段页岩气井套管下放难度,提高下套管时效和安全度;(2)研制的高效洗油冲洗隔离液体系在常温至120℃下的冲洗效率均大于90%,能够保证水泥浆对油基钻井液的顶替效率和井壁的有效胶结;(3)确定了该区长水平段固井韧性防窜水泥浆凝固后的性能——水泥石弹性模量应小于7 GPa、三轴强度最好大于40 MPa,以减轻和避免压裂时的水泥环破坏;(4)形成的钻井液调整、预应力固井、地面高压泵注工艺等配套技术提高了页岩气井固井质量。2015—2016年期间运用上述系列固井技术在四川盆地开展了85口井固井作业,平均井深4 832 m,平均水平段长1 560 m,固井质量优质率达89.58%;水平井固井后候凝期间无环空带压,钻完井及试油期间环空气窜得到明显改善。结论认为,该配套技术可以保证并提高长水平段页岩气井的固井质量。

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 ℃, 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 4 832 m, the average length of horizontal sections is 1 560 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.