页岩气水力压裂裂缝缝网完善程度概论

受页岩气实际储层条件和施工工艺技术的限制,相同或相近的改造体积内的人工裂缝网络分布状态千差万别。仅用改造过的页岩气藏体积(SRV)进行改造效果的表征和评价,有可能导致评估认识上的偏差甚至错误。为此,利用人工裂缝扩展数值模拟技术和产能数值模拟技术,研究了人工裂缝和天然裂缝的空间分布状态、改造过的页岩气藏内部的压力状态和采出程度,提出了页岩气缝网、理想缝网、页岩缝网完善程度3个概念。研究成果表明:(1)在开采结束时,各目标区域根据被改造过页岩气藏内气体采出程度和生产时间,可以划分成"改造相对完善区""改造过渡区"和"改造不完善区"等3类;(2)缝网最终形态参数和储层特性是影响缝网完善程度的两个主要因素,对于特定的气藏在井眼轨迹给定的情况下,人工裂缝的方向、长度、导流、高度和空间位置是影响页岩气缝网完善程度主要因素。结论认为,页岩气水力压裂裂缝缝网完善程度理论的提出,丰富了页岩储层改造技术理论体系,对致密油气等其他非常规储层裂缝系统的表征也具有借鉴作用。

Introduction to the completion degree of hydraulic fracture networks in shale gas reservoirs

Due to the limitation of actual shale gas reservoir conditions and fracturing technologies, artificial fracture networks are differentgreatly even in the same or similar stimulated reservoir volume. Deviations and even faults occur in evaluation and cognition if only the stimulated reservoir volume (SRV) is used to characterize and evaluate the effect of stimulation. In this paper, the spatial distribution of artificial fractures and natural fractures and the internal pressure state and degree of reserve recovery of stimulated shale gas reservoirs were studied by means of artificial fracture propagation numerical simulation and production numerical simulation. And three concepts were proposed, i.e., shale gas fracture network, ideal fracture network and completion degree of fracture network. The study results indicatethat, at the end of reservoir development, target zones can be classified into three types (i.e., relatively completed stimulation zone, transitional stimulation zone, and uncompleted stimulation zone) according to the recovery degree and production time of stimulated reservoirs; and that the final morphologic parameter of fracture networks and the reservoir characteristic are two main factors affecting the completion degree of fracture networks. As for a specific gas reservoir, the orientation, length, conduction, height and spatial location of its fracture network are the main factors influencing its completion degree if the well trajectory is set. The proposal of the theory on the completion degree of hydraulic fracture networks in shale gas reservoir enriches the theoretical system of shale reservoir stimulation technology, and it can be used as the reference for characterizing the fracture systems in other unconventional reservoirs, such as tight oil and gas reservoirs.