四川盆地深层超深层碳酸盐岩水平井分段酸压关键技术

Horizontal well staged acid fracturing technology for deep and ultra-deep carbonate gas reservoirs in the Sichuan Basin

油气勘探开发向深层(4500~6000 m)、超深层(≥6000 m)进军是未来的重要方向和必然选择。为了解决四川盆地深层超深层碳酸盐岩气藏高温条件下酸蚀裂缝长度短、高闭合应力下导流能力低、笼统改造针对性差、单井产量低的难题,通过开展真三轴酸压物模和酸压工艺模拟实验,有针对性地优化了不同类型储层酸压工艺,结合地质工程一体化精细分段布缝,配套裸眼分段工具和暂堵转向材料,实现了深层超深层长水平井段强非均质储层“一段一策”的精准改造。研究结果表明:①低水平应力差(≤10 MPa)条件下天然裂缝发育储层采用低黏度酸液体系可激活并刻蚀天然裂缝形成复杂裂缝,高水平应力差(≥15 MPa)条件下酸压裂缝受地应力控制而形成双翼裂缝;②采用大尺寸岩板“接力”注酸方法实现了酸蚀裂缝有效长度、全缝长导流能力分布的室内实验测试,优化了满足不同类型储层改造需求的酸压工艺;③优化了超深水平井裸眼封隔器分段管柱结构,刷新了8600 m超深水平井裸眼封隔器分段酸压纪录,优选了暂堵剂组合和配比,有效封堵2~6 mm裂缝,承压能力达4.2~24.9 MPa,满足缝口、缝内暂堵转向需求。结论认为,研究成果形成了深层超深层碳酸盐岩水平井分段酸压关键技术,天然气增产效果显著,井均增产4.8倍,为同类气藏高效改造提供了有益借鉴,为建设西南“气大庆”奠定了技术基础。

Deep(4500–6000 m)and ultra-deep(≥6000 m)reservoirs are critical targets and inevitable options for future petroleum exploration and development.In the Sichuan Basin,deep and ultra-deep carbonate gas reservoirs exhibit short acid-etched fractures under high temperature,low conductivity under high closure stress,poor pertinence of commingled stimulation treatment,and low singlewell productivity.In view of these problems,true triaxial acid fracturing physical simulation and acid fracturing technique simulation experiments are performed to optimize the acid fracturing technique for a specific type of reservoir.Then,based on geology–engineering integrated fine stage division for fracturing,in combination with the openhole staged fracturing tools and the temporary plugging and diverting(TPD)materials,a precise fracturing stimulation is realized by“one stage,one policy”for deep and ultra-deep,highly heterogeneous reservoirs with long horizontal sections.The results show that,under low horizontal stress difference(≤10 MPa),reservoirs with natural fractures can be stimulated by using the low-viscosity acid system and natural fractures can be etched to form complex fractures;under high horizontal stress difference(≥15 MPa),acid-fracturing-induced fractures are controlled by in-situ stress to form biwing fractures.A laboratory test was conducted by means of“relayed”acid injection with large-scale rock plates to identify the distribution of conductivity in the effective length and full length of acid-etched fractures,so that the acid fracturing technique was optimized depending upon the requirements for stimulating different types of reservoirs.The structure of openhole packer staged fracturing string for ultra-deep horizontal wells is optimized,enabling the ultra-deep horizontal well openhole packer staged acid fracturing to apply at a record depth of 8600 m.Moreover,the combination and proportion of temporary plugging agents are optimized,which helps effectively plug 2–6 mm fractures and realize a loading capacity of 4.2–24.9 MPa,meeting the requirements for temporary plugging and diverting at the gap and within fractures.It is concluded that the horizontal well staged acid fracturing technique for deep and ultra-deep carbonate reservoirs can significantly enhance well productivity by 4.8 times on average.The technique provides a useful reference for efficient stimulation of similar carbonate gas reservoirs and lays a technical foundation for building"Daqing-scale Gas Fields"in southwest China.