油藏型储气库断层封闭性综合评价——以堡古2区块为例

Comprehensive evaluation of fault sealing in oil reservoir type gas storage facilities:a case study of Pugu 2 Block

断层封闭性评价不仅对油气成藏机理与富集规律研究具有重要指导意义,更是油藏改建储气库前期地质评价的重要内容。为进一步论证堡古2油藏改建储气库的地质可行性,基于断层对上覆东三段盖层完整性的影响,建立了断层分类评价方案,从垂向与侧向2个方面评价断层的静态封闭性,利用断层活化开启压力与断层滑移失稳指数评价断层的动态封闭性,进而采用层次分析法构建断层封闭性综合评价模型,提出断层综合封闭性评价标准。研究结果表明:堡古2区块发育的11条正断层可划分为3类;断层断面正压力普遍超过8 MPa,断层两盘以砂-泥对接为主,断层泥比率(shale gouge ratio,SGR)普遍大于40%、断层开启系数(FOI)介于0.58~1.20,断层静态封闭性良好;断层活化开启临界压力超过70 MPa,明显高于地层流体压力,断层滑移指数介于0.17~0.56,均小于0.60,说明断层动态封闭性良好;11条断层封闭性综合评价指数(T)为0.93~1.15,断层封闭性良好。建立了断层封闭性综合评价标准,研究成果可为南堡凹陷乃至渤海湾盆地油气藏型储气库断层封闭性评价提供指导。

The evaluation of fault sealing is not only of great guiding significance for the study of oil and gas accumulation mechanism and enrichment law,but also an important content in geological evaluation at the early stage of reservoir reconstruction and gas storage.To further demonstrate the geological feasibility of renovating the gas storage reservoir in the Pugu 2 oil reservoir,a fault classification evaluation scheme was established herein based on the effects of faults on the integrity of the overlying cap rock of the third member of Dongying Formation.The static sealing performance of faults was evaluated from both vertical and lateral aspects.The dynamic sealing performance of faults was evaluated using the activation opening pressure of faults and the sliding instability index of faults.Then,the analytic hierarchy process was used to construct a comprehensive evaluation model for fault sealing,and a comprehensive sealing performance evaluation standard for faults was proposed.The research results indicate that the 11 normal faults developed in Pugu 2 Block can be divided into three categories.The normal pressure of the fault section generally exceeds 8 MPa,while the two walls of the fault are mainly connected by sand and mud.The SGR is generally greater than 40%,and the FOI is between 0.58 and 1.20.Fault has good static sealing.Moreover,the critical pressure for fault activation exceeds 70 MPa,which is significantly higher than the stratum fluid pressure.The fault slip index ranges from 0.17 to 0.56,all of which are less than 0.60,indicating good dynamic sealing of the fault.The sealing comprehensive evaluation index(T)of 11 faults ranges from 0.93 to 1.15,indicating good fault sealing.Finally,a comprehensive evaluation standard for fault sealing has been established,and the research results can provide guidance for the fault sealing evaluation of oil and gas reservoirs in both the Nanpu Depression and the whole Bohai Bay Basin.