碎屑岩地层中不同结构断层岩封闭能力定量评价

This project is aimed at the scientific problem of the analogy between fault rock and clastic rock by the method of difference between fault and reservoir entry pressure for quantitative evaluation of fault rock sealing ability, studied the distribution regularities and genetic relationship in different structures of fault rock by annular shear test which could simulated the fragmentation process of fault fillings. Based on the structures of fault fillings in different stages of fragmentation, the lithology of clastic rock which could analogy with fault rock and has the same structural characteristics can be identified, then determined the relation between critical point of different structures and fault slip distance, established the evaluation template between clay content with the critical ratio of clay/sand layer thickness and fault slip distance, analyzed the fragmentation stage and position of fault rock which at breakpoint quantitatively. By establishing the integral mathematical model between diagenetic pressure and diagenetic time of fault rock as well as that of clastic rock, calculated the profile position and entry pressure of clastic rock which could compare to the target fault rock and has the same diagenetic degree, regarded this pressure as the entry pressure of fault rock, and then quantitatively evaluated the sealing ability of fault rock by comparing the entry pressure between fault rock and reservoir rock. The research results could fill the uncertainly of the study on sealing ability of faults in clastic layers, the considering factors are more in line with the underground realities. It is of great significance to reduce the drilling risk of fault-related traps and to enrich the geological theory of oil and gas.

本项目针对利用断-储排替压力差法定量评价断层岩封闭能力存在的断层岩与碎屑岩可类比性的科学问题，通过环形剪切实验模拟断裂充填物的碎化过程，研究不同结构断层岩的分布规律及成因关系，根据不同碎化阶段断裂充填物的结构确认具有该结构特征的断层岩岩性和可与之类比的碎屑岩岩性，明确不同结构变化临界点与所研究的断层断移距离关系，建立断层岩泥质含量与临界厚距比的评价模版，分析断点处断层岩的碎化阶段及位置，通过建立断层岩成岩压力和成岩时间与相同泥质含量碎屑岩的成岩压力和成岩时间的积分数学模型，计算与该断层岩可类比的、成岩程度相当的碎屑岩所在剖面位置及排替压力，以该排替压力代替断层岩排替压力，比较其与储层岩石排替压力的相对大小定量评价断层岩封闭能力。研究成果填补了碎屑岩地层中断层岩封闭能力研究的不确定性，考虑的因素更符合地下实际情况，对降低断层相关圈闭钻探风险及丰富油气地质理论均具有重要意义。

随着油气勘探开发向被断层复杂化区域的不断深入，断层封闭性研究已经成为油气地质研究者不可避开的重要工作，以往的研究没有考虑断层岩与碎屑岩结构的差异性，且忽略了岩石的成岩过程是成岩压力在成岩时间内的累积，均造成了断层岩封闭能力评价精度的降低。本项目通过环形剪切物理模拟实验模拟断裂充填物的碎化过程，研究不同结构断层岩的分布规律，根据不同碎化阶段断裂充填物的结构，确认具有该结构特征的断层岩岩性和可与之类比的碎屑岩岩性，建立断层岩泥质含量与临界厚距比的评价模版，通过建立断层岩成岩压力和成岩时间与相同泥质含量碎屑岩的成岩压力和成岩时间的积分数学模型，计算与该断层岩可类比的、成岩程度相当的碎屑岩所在剖面位置及排替压力，以该排替压力代替断层岩排替压力，比较其与储层岩石排替压力的相对大小定量评价断层岩封闭能力。主要取得了以下几点认识：①在相同砂泥配置条件下，随着断层滑动位移增加，颗粒破碎程度增大，颗粒直径和孔隙直径减小，断层带厚度增加，孔隙度和渗透率减小，封闭能力增强，断层岩先后经历以断层角砾为主（I）、以砂岩碎屑为主（II）、砂粒与泥质混合（III）、断层泥（IV）4个碎化阶段。②断层岩及碎屑岩在成岩过程中，其成岩程度是垂向应力及水平地应力随成岩时间增大而不断累加的变量，渤海湾盆地大港探区张北断层评价结果表明，张14-1井在不同深度处断层岩处于II、III碎化阶段，断-储排替压力差约为-3.299~4.154MPa，评价结果与实际钻探结果吻合程度较好，在定量评价碎屑岩地层中不同结构断层岩的封闭能力时具有一定的合理性和准确性。研究成果填补了碎屑岩地层中断层岩封闭能力研究的不确定性，考虑的因素更符合地下实际情况，对降低碎屑岩地层中断层相关圈闭钻探风险、提高断层发育区油气成藏规律的认识以及丰富油气地质理论均具有重要意义。