特低渗油藏非稳态周期注水机理及应用

为了充分发挥储层裂缝与基质之间的渗吸作用，增大注水波及体积，提高水驱采收率，以延长X区块长6油藏为研究对象，利用室内静态渗吸实验分析逆向渗吸影响因素，并采用考虑渗吸作用的数值模拟技术对X区块周期注水进行参数优化。结果表明，X区块渗吸方式主要为逆向渗吸，且储层渗透率、孔隙度的增大可以提高渗吸驱油效率；随着含水饱和度的增加，渗吸驱油效率降低；界面张力与渗吸驱油效率在一定范围内呈反比关系；X区块注水生产时，优选非稳态的周期注水方式，其优化工作制度为注20 d停30 d、注采比1.0~1.2、注水量8~12 m3/d。通过矿场现场实施，区块产油量小幅增加，含水率明显降低，较连续性注水开发方式可提高采收率2.5~3.5百分点，为特低渗油藏非稳态周期注水开发提供了有效的理论基础及现场应用依据。

Mechanism and application of transient cyclic water flooding in extra-low permeability oil reservoirs

The Chang 6 oil reservoir in the Block X of Yanchang was taken as the research object in order to give full play to the imbibition between reservoir fractures and matrix, increase the waterflooding swept volume and improve the waterflooding recovery factor. After the influence factors of counter-current imbibition were analyzed by conducting laboratory static imbibition experiments, the parameters of cyclic water flooding in the Block X were optimized be means of numerical simulation technology considering imbibition. It is indicated that counter-current imbibition is the main imbibition mode in the Block X. The imbibition displacement efficiency increases with the increase of reservoir permeability and porosity and decreases with the increase of water saturation. In a certain range, interfacial tension and imbibition displacement efficiency are in an inverse relation. Transient cyclic water flooding is selected in the Block X and its optimized working system is injection for 20 d and stop for 30 d with injection/production ratio of 1.0?1.2 and water injection rate of 8?12 m3/d. Field application results show that oil production rate increases slightly, water cut decreases significantly and recovery factor is 2.5?3.5% higher than that of continuous waterflooding development. The research results provide the effective theoretical foundation and field application basis for the transient cyclic waterflooding development of extra-low permeability oil reservoirs.