延长东部油田主力油层平均中深670 m、平均渗透率0.3~0.5 mD,为特超低渗浅层油藏,油井压裂时易形成水平裂缝,致使注水开发过程中油井出现快速水淹,造成油井产量大幅下降,采收率低。针对这一问题,在对水平缝注水渗流特征、压裂水平缝油井水淹规律和底部注水机理研究的基础上,提出了底部注水开发方式,并应用渗透率变异系数、突进系数、级差3个参数综合表征水窜层位与非水窜层位特征,为底部注水选层提供依据;通过室内核磁共振在线测试及岩心流动驱替实验,结合油藏数值模拟和现场示踪剂测试等综合手段,对注水参数进行了优化。开展底部注水先导性试验的3个井组单井产油量由0.054 t/d提高到0.179 t/d,含水率由15%下降到10%,地层压力提高了0.18 MPa,预测最终采收率提高了2.1个百分点,取得了较好效果。研究表明,当渗透率变异系数＜0.5、突进系数＜1.5、渗透率级差＜5,注入速度为0.06 mL/min,注水压力7 MPa时,注水开发效果最好。底部注水能够有效解决浅层水平缝油藏注水开发效果不佳的问题,为同类油藏的高效注水开发提供了参考。

The primary oil layer of the Yanchang East Oilfield are situated with an average depth of 670 meters and possess an average permeability of 0.3~0.5 mD. This marks it as an ultra-low permeability shallow oil reservoir. Horizontal fractures are easily formed during oil well fracturing, resulting in rapid water flooding when water injection development is conducted. This results in a significant decrease in oil well production and low recovery rate. To address this challenge, a bottom water injection development method is proposed based on the study of the characteristics of horizontal fracture water injection seepage, the water flooding pattern of fractured horizontal fracture oil wells, and the mechanism of bottom water injection. Three parameters, specifically permeability variation coefficient, breakthrough coefficient, and grade difference, are applied to comprehensively characterize the characteristics of water breakthrough and non-water breakthrough layers, thereby providing a basis for bottom water injection layer selection. Indoor nuclear magnetic resonance online testing and core flow displacement experiments are conducted in conjunction with reservoir numerical simulation and on-site tracer testing to optimize the water injection parameters. The individual well oil production of the three well groups conducting bottom water injection pilot tests rose from 0.054 t/d to 0.179 t/d. The water content decreased from 15% to 10%, the formation pressure grew by 0.18 MPa, and the predicted final recovery rate escalated by 2.1 percentage points, delivering impressive results. Research has shown that the water injection development effect is optimal when the coefficient of variation of permeability is less than 0.5, the breakthrough coefficient is less than 1.5, the permeability level difference is less than 5, the injection rate is 0.06 mL/min, and the injection pressure is 7 MPa. Bottom water injection can effectively solve the issue of poor water injection development effect in shallow horizontal fracture reservoirs, providing reference for efficient water injection development in reservoirs of the same nature.