基于构造物理模拟实验的正断层形成和演化过程

研究正断层的形成和演化过程不仅对厘清石油、天然气的聚散过程具有重要意义,而且可为断块油气藏等的高效开发提供理论依据.以鄂尔多斯盆地延长组正断层为原型开展构造物理模拟实验;通过高分辨率的粒子图像测速技术记录实验砂层变形速度、断层倾角、断层距离和应变能;划分正断层形成和演化阶段并从应变能角度分析正断层形成和演化特征.结果 表明:正断层开始形成后,断层破碎带区域最早破裂,上盘次之,其后为下盘;倾角随埋深加深有"多期递减"现象;明显断距最先在断层带上部出现,断距不断增大后断裂向断层带下部延展;断层带纵向上断距并不均等,断层带下部断裂程度明显大于上部,断距分布呈"双峰"特征.正断层形成和演化可划分为断层初始期、断层孕育期、断层形成期、断层稳定期,不同时期的应变能密度峰值差异为1～3个数量级.应变能的释放时间决定了断裂产生时机,应变能释放率决定了断裂规模,地层应变能的积累和释放是正断层形成和演化的主要内因.正断层形成后,残余了高应变能的上盘区域以多种形式逐渐释放应变能形成次生断层.文中提供了一种模拟正断层形成和演化的物理模拟实验方法,希望给石油地质工作者提供一点有益的启发.

Study on normal fault formation and evolution based on structural physical simulation experiment

Studying the formation and evolution process of normal faults is not only of great significance for clarifying the accumulation and dispersion process of oil and natural gas, but also provides theoretical basis for the efficient development of fault-block oil and gas reservoirs. Take the normal fault of the Yanchang Formation in the Ordos Basin as a prototype to carry out structural physical simulation experiments; use high-resolution particle image velocimetry to record the experimental sand deformation speed, fault dip, fault distance, and strain energy; divide the formation and evolution stages of normal faults and start strain Ability to analyze the formation and evolution characteristics of normal faults. The results show that after the formation of normal faults, the fault fracture zone ruptures first, followed by the hanging wall, followed by the footwall; the dip angle has a phenomenon of "multi-stage decline" as the depth of burial deepens; the obvious fault distance appears first in the upper part of the fault zone After the fault distance increases, the fault extends to the lower part of the fault zone; the fault distance in the longitudinal direction of the fault zone is not uniform, the fault degree in the lower part of the fault zone is obviously greater than that in the upper part, and the fault distance distribution shows a "double peak" characteristic. The formation and evolution of normal faults can be divided into fault initial period, fault incubation period, fault formation period, and fault stable period. The peak strain energy density difference in different periods is 1 to 3 orders of magnitude. The release time of strain energy determines the timing of the fracture, and the rate of strain energy release determines the scale of the fracture. The accumulation and release of strain energy in the formation is the main internal cause of the formation and evolution of normal faults. After the normal fault is formed, the area of the hanging wall with high strain energy is gradually released in various forms to form a secondary fault. This article provides a physical simulation experiment method for simulating the formation and evolution of normal faults, hoping to provide some useful inspiration for petroleum geologists.