四川盆地南部地区(以下简称川南地区)页岩气水平井体积压裂改造过程中,受地质及工程等因素影响,水力裂缝易与单一方向大尺度天然裂缝沟通并过度扩展,从而诱导邻井压力快速上涨,最终导致压裂窜扰、套管变形等问题,直接影响页岩气单井产量.为此,针对川南地区页岩气储层压裂窜扰模式多样、机制认识不清以及防控效果有限等问题,建立了全耦合页岩气水平井压裂多簇同步扩展数值模拟模型,并阐明了不同类型压裂窜扰的影响规律,最后提出了有效治理压裂窜扰的方法.研究结果表明:①天然裂缝发育的储层中,水平井裂缝易沿单一方向大尺度天然裂缝优势条带扩展,直接或间接对邻井产生影响,造成其压力涨幅异常;②页岩气水平井通过避免在风险段压裂或降低改造强度在一定程度上可减轻压裂窜扰的影响:③压裂井附近存在衰竭邻井时,裂缝更易往邻井低应力区扩展产生压裂窜扰,窜扰程度与岩石孔隙弹性密切相关.结论认为,合理避开风险段射孔、控制压裂改造强度可有效降低页岩气水平井压裂窜扰的风险,该研究成果可为同类国内外页岩气区块页岩气水平井压裂开发提供技术指导.
In the process of volumetric fracturing of shale gas reservoirs by horizontal well volume fracturing in the southern Sichuan Basin,geological and engineering factors make it easy for hydraulic fractures to communicate with large-scale natural fractures in a single direction and propagate excessively,inducing rapid pressure increase in adjacent wells.This ultimately results in frac hits,casing deformation and other problems,which have a direct effect on the shale gas production of individual wells.To address the diverse patterns of frac hits,unclear understanding of mechanisms,and limited effectiveness of control measures in shale gas reservoirs of the southern Sichuan Basin,this paper establishes a fully-coupled numerical simulation model for multi cluster synchronous expansion of shale gas horizontal well fracturing.Then,the impact patterns of different types of frac hits are illustrated.Finally,the effective methods for treating frac hits are proposed.And the following research results are obtained.First,in the reservoirs with developed natural fractures,the fractures induced by horizontal well volume fracturing tend to propagate along the dominant bands of large-scale natural fractures in a single direction,which has a direct or indirect impact on adjacent wells,causing abnormal pressure increase.Second,the impact of frac hits can be alleviated to some extent if a shale gas horizontal well avoids fracturing in high-risk stages or the fracturing intensity is reduced.Third,when there is a depleted adjacent well near the fractured well,fractures are more likely to propagate to the low-stress zones of the adjacent well,resulting in frac hits,and the extent of frac hits is closely related to the elastic properties of rock pores.In conclusion,frac hits of shale gas horizontal wells can be reduced effectively by avoiding perforating in high-risk stages and controlling fracturing intensity reasonably.The research results can provide technical guidance for the fracturing development of shale gas reservoirs by horizontal well volume fracturing in similar shale gas blocks at home and abroad.