低渗透油藏水驱动态裂缝数学模型及数值模拟

A mathematical model and numerical simulation of waterflood induced dynamic fractures of low permeability reservoirs

基于低渗透油田资料,提出了动态裂缝的概念并分析动态裂缝起裂、延伸、趋于闭合的演化过程,建立了可以描述裂缝形态及属性动态变化的数学模型并编制油藏数值模拟软件。数值模拟表明,注入压力高于地层破裂压力时动态裂缝随即起裂,此后逐步向前延伸,与地层压力和注入量呈周期性变化;实施温和注水后,动态裂缝在较长时期内仍维持开启,随后裂缝整体迅速趋于闭合,说明动态裂缝受生产动态因素影响明显。动态裂缝的存在使注入水沿着裂缝窜进,随着动态裂缝的逐步延伸,注入水形成狭长的驱替范围,造成水驱严重不均衡,加剧低渗透储集层的非均质性,同时显著影响各方向油井的含水上升规律。但动态裂缝对注采井间有效驱替系统的建立起着积极作用。

Based on abundant data of low permeability oilfields, dynamic fractures were conceptualized and their evolution, including cracking, extending and closing, were analyzed. A new model that describes the dynamic changes of fracture shape and properties was established and a software module was developed. The simulation results show that dynamic fractures cracked once the injection pressure was higher than the formation fracture pressure, and then extended continually, which showed a periodic variation relationship with the formation pressure and the injection volume. After the moderate injection, dynamic fractures remained the open status in a relatively long time, but then the whole fractures tended to close quickly, and these phenomena indicate that the dynamic fractures were significantly affected by the production condition. The presence of dynamic fractures provides a channel for the injection water. With the gradual extension of dynamic fractures, the injection water forms a narrow range of displacement, which leads to the severe imbalance of water flooding, aggravates the heterogeneity of low permeability reservoirs, and significantly affects the water cut rising rules of wells in all directions. However, dynamic fractures also show a positive effect on the establishment of an effective displacement system between the injection wells and the production wells.