松辽盆地敖南油田CO_(2)驱油藏断层封闭性定量评价

Quantitative evaluation of fault sealing of CO_(2)drive reservoirs in Aonan oilfield of Songliao Basin

敖南油田经历二十多年的注水开发,面临着已开发区块采油速度慢、欠注井比例高、地层压力保持水平低等问题。实施气驱开发是保持地层压力、提高采收率、降低生产成本的重要手段。但在高注入压力的条件下,注入的CO_(2)可能沿断层发生渗漏,因此,定量评价断层封闭性对于气驱油藏的开发方案设计和油田安全生产有着极为重要的意义。依据典型岩石样品排替压力和泥质含量测试结果,建立排替压力与深度、泥质含量的定量关系式,采用断层-地质模型和三维应力模型对敖南油田的断层封闭性进行了定量评价。结果表明:敖南油田的边界断层原始渗漏临界压力为0~12 MPa,渗漏风险区分布在储层砂岩对接程度较高的井组和不同断层交界附近,其临界压力为0~4 MPa;在井位优化设计时风险区附近要预留安全距离,注气井要避开高渗漏风险断层,或在注入井与断层间设计采出井以降低储层压力,降低CO_(2)沿断层渗漏的风险。研究结果可以为CO_(2)驱油藏的开发方案设计提供有效依据。

Aonan oilfield has experienced more than 20 years water flooding development,facing challenges of low oil production rate,high proportion of under-injection wells and low formation pressure maintenance level in developed blocks.Implementing gas drive development is an important means to maintain formation pressure,improve oil recovery and reduce production costs.However,in condition of high injection pressure,injected CO_(2)may leak along faults.Therefore,quantitative evaluation of fault sealing is very important for development scheme design of gas drive reservoirs and safe production of oilfield.Quantitative relationship formula of displacement pressure with depth and shale content is established based on test results of displacement pressure and shale content of typical rock samples.Fault sealing of Aonan oilfield is quantitatively evaluated by fault-geological model and 3D stress model.The results show original leakage critical pressure of boundary faults in Aonan oilfield is 0~12 MPa.Leakage risk areas are distributed in well patterns with high reservoir sandstone juxtaposition degree and near intersections of different faults,with critical pressure of 0~4 MPa.When optimizing well locations design,safe distance should be reserved near risk area,with gas injection wells avoiding high leakage risk faults or production wells designed between injection wells and faults to reduce reservoir pressure and reduce the risk of CO_(2)leakage along faults.The research provides effective basis for reservoir development scheme design of CO_(2)flooding.