基于相场裂缝模型的酸化压裂孔洞沟通类型研究

Connection types of natural holes and acid fractures based on a phase-field fracture model

塔河油田深层碳酸盐岩储层油气分布具有不均匀性,大量油气资源储存在天然溶洞内部。通过酸压裂缝沟通尽可能多的孔洞结构,建立孔洞与井筒之间的流通通道,有利于提高深层碳酸盐岩储层开发改造效果。本文根据拉伸—剪切复合型裂缝扩展准则对传统相场裂缝模型能量方程进行修正,开发了扩展自适应网格技术。基于相场法建立流—固—热—化多场耦合酸压裂缝扩展数值模型,分析了地应力、孔洞结构与酸岩反应对酸压裂缝扩展路径的影响。根据模拟结果发现:(1)根据相场法建立的酸压裂缝模型基于能量最小化原理求解裂缝扩展路径,能够实现流—固—热—化多场耦合条件下酸压裂缝起裂与扩展模拟。(2)地应力对酸压裂缝扩展起主导作用,孔洞结构对酸压裂缝扩展起诱导作用,酸岩反应对酸压裂缝扩展起辅助作用。(3)酸压裂缝周边的孔洞可在酸液的扩散与酸蚀作用下与裂缝达成间接沟通,孔洞内的油气资源可通过酸蚀后的基质进入酸压裂缝。有效识别孔洞结构分布位置是提升缝洞型储层酸压开发效果的基础。本文研究结果可为深层碳酸盐岩储层酸化压裂缝洞沟通行为提供理论依据。

The significant amount of oil and gas resources in the Taha oilfield is stored in natural holes.Acid-fracturing can establish fluid communication pathways between natural holes and wellbores,which can increase the development of carbonate reservoirs.An extended adaptive meshing technique was developed in this paper.The multi-physics coupling model for acid-fracture propagation was established using the phase-field method.The interaction between acid fractures and natural holes was simulated.The effects of in-situ stress,hole structure,and acid-rock reactions on acid-fracture propagation were analyzed.Two communication modes between acid-fractures and natural holes,direct communication and indirect communication,were summarized.The simulation results reveal the following conclusions:(1)the acid fracture model based on the phase field method solves the fracture propagation path based on the principle of energy minimization,which can simulate the acid fracture initiation and propagation under multi-field coupling conditions.(2)In-situ stress plays a dominant role in acid-fracture propagation.Natural holes affect the propagation of acid fracturing,and acid rock reaction assists in the propagation of acid fracturing.(3)The acid diffusion and etching capabilities result in indirect communication between acid fractures and surrounding holes,The oil and gas resources in the holes can enter the acid fracture through the acid-etched matrix.The identification of the holes distribution is the basis of improving the acid fracturing result.It is believed that this finding can offer information for acid-fracturing study in deep carbonate reservoirs.