页岩气超长水平井预控水泥环封固失效水泥浆技术

Cement slurry technology for preventing and controlling cement sheath integrity failure in ultra-long horizontal shale gas wells

页岩气超长水平井储层改造时,需进行多段的水力压裂施工,水平段水泥环在多次循环载荷下的密封完整性问题尤为重要。为此,基于岩石微裂纹的演化过程,设计了一种Superflex增韧剂,强化微裂纹处纤维的桥连作用,增强微裂缝尖端弹塑性,阻断微裂纹扩展,降低水泥石塑性形变,从而可以有效预防和控制水泥环封固失效。基于此增韧剂,构建了抗循环载荷弹韧防气窜水泥浆体系,采用常规评价仪器、高温高压岩石流变仪和页岩物性测定仪等手段,综合测试了水泥浆常规性能及防气窜性能,重点讨论了水泥石的强度和韧性特性,并评价了该水泥浆体系的现场适用性。研究结果表明:①Superflex增韧剂与水泥浆相容性好,不影响水泥浆体系的其他性能,且在不牺牲强度的前提下,改善了水泥石的弹韧性。②抗循环载荷弹韧防气窜水泥石承受循环载荷70次后,塑性形变小,保持完整,具有良好的抗循环载荷能力,能够有效地预控超长水平井水泥环封固失效问题。③该水泥浆体系现场应用于水平段长2700余米的超长水平井,固井质量优良,经分段压裂后,环空不带压,显示了较好的工程应用效果。

Multi-stage hydraulic fracturing is usually performed to stimulate reservoirs in ultra-long horizontal shale gas wells.The sealing integrity of the cement sheath in the horizontal section under multiple cyclic loads is particularly important.According to the evolution process of rock micro-cracks,a Superflex flexibilizer was designed to strengthen the bridging effect of fibers at the micro-cracks,enhance the elastic-plasticity of the micro-crack tips,block the expansion of micro-cracks,and reduce the plastic deformation of set cement,thereby preventing and controlling the failure of cement sheath.Based on this flexibilizer,an elastic-tough cement slurry system of anti-cyclic load and gas-channeling prevention was constructed.By using conventional evaluation instruments,HT/HP rock rheometers,and shale physical property tester,the regular performance and anti-gas-channeling performance of the slurry were comprehensively tested.Furthermore,the strength and toughness of set cement were discussed specially,and the field applicability of the system was evaluated.Results show that(1)the Superflex flexibilizer has good compatibility with cement slurry,does not affect other properties of the system,and improves the elasticity and toughness of set cement without sacrificing its strength;(2)after 70 times of cyclic load,the set cement remains intact with small plastic deformation,showing a good anti-cyclic loading capability,which can effectively prevent and control the integrity failure of cement sheath in ultra-long horizontal wells;and(3)the cement slurry system was applied to an ultra-long horizontal well with a horizontal section of more than 2700 m,revealing excellent cementing quality,and the annulus was free of pressure after staged fracturing.Thus,the system is proved with effective engineering application.