Youqi dizhi yu caishoulu (Sep 2024)
Research on flow mechanism and development law of Jiyang shale oil
Abstract
Jiyang shale oil resources have enormous potential. However， there is a lack of systematic understanding of seepage mechanism and development laws in the multi-scale spaces after fracturing due to the influence of complex geological conditions， making it difficult to achieve large-scale beneficial development. In order to clarify the formation mechanism of the development law of Jiyang shale oil， the multi-scale fracture characteristics of Jiyang shale oil were analyzed. The formation mechanism and combination mode of fracture networks after fracturing were studied using physical experiments and numerical simulations. In addition， seepage mechanisms in multi-medium spaces were researched， including the stress sensitivity of multi-scale fractures， nonlinear flow in multi-scale pores and fractures， and imbibition displacement of pore-fracture systems. According to the differences in the distribution of multi-scale fracture networks and their flow laws after fracturing， a three-zone flow pattern of “easy flow-slow flow-difficult flow” for shale oil was established. Finally， the flow characteristics and production laws of Jiyang shale oil at different flow stages were clarified. The research results indicated that the developed bedding fractures could improve the physical properties of reservoirs， enhance imbibition displacement efficiency， and reduce start-up pressure gradient. During the elastic development stage， the flow channels reduce， and the fracture network conductivity decreases as the formation pressure declines， resulting in significant stress sensitivity. In the development process of Jiyang shale oil， the initial flow state is mainly dominated by linear flow and elliptical flow of fractures supplied by the easy flow zone. In the middle stage of development， the slow flow zone supplies energy to the easy flow zone， and the flow state changes to elliptical flow in the formation. Moreover， the shale oil in the difficult flow zone is gradually produced， and the flow state changes to boundary-controlled flow in the later stage of development. Due to the influence of geological conditions and production systems， there are significant differences in the energy change， water cut decrease， and production change law of different horizontal wells. Reasonably optimizing the shut-in time and production system can ensure imbibition displacement efficiency， efficiently utilize formation energy， and improve shale oil production capacity.
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