碳酸盐岩层系断层封闭机理研究

Faultsealing mechanisms in the carbonate sequence

基于周口店八角寨雾迷山组碳酸盐岩露头断层密度、断层内部结构和断裂带泥质质量分数的分析,结合岩石形变三维应力数值模拟及塔中碳酸盐岩油藏岩心和薄片多期方解石交切胶结关系,揭示了碳酸盐岩层系断层封闭机理,提出了一种精确测定碳酸盐岩中泥质质量分数的实验方法.研究结果表明:该断裂带具有明显的二元结构特征,主断层核部岩石破碎程度大,断层密度高,随着远离主断层,断层密度大体呈指数降低;围岩碳酸盐中泥质质量分数一般为10%～15%,而在断层核部位,泥质质量分数增加到30%～40%,明显增加了2～3倍,同时,随着远离断层核的部位,泥质质量分数稳定下降,说明在碳酸盐岩层系的断层中,高泥质含量仍然是断层封闭的最重要的机理之一;岩性组成及含量的不同也会导致岩石在应变形态上的差别;碳酸盐矿物特别是方解石脉多期交切、结晶现象在破碎带中广泛分布,说明胶结作用是影响碳酸盐岩层系断层封闭的另一个重要因素.

This study took into account the analysis of fault density,fault’ internal structure and shale mass fraction of the fault zone in ourcrop of Wumishan formation,Bajiaozhai,Zhoukoudian,and also considered the three-dimensional stress numerical simulation and the calcite cross-cut cement relationships in core and microscope observation of carbonate reservoir in Tazhong area.With those in consideration,this study revealed the fault sealing mechanisms in the carbonate sequence,and proposed an experimental method to accurately determine the clay content of the carbonate.The results show that： fault zone has the obvious characteristics of dual structure;the rock in the core part of main fault is gravely damaged,and the fault density is high;with an increase of distance from fault nuclear,and the fault density reduces exponentially;for the surrounding rock,the shale mass fraction of carbonate ranges from 10% to 15%,while for the part of fault nuclear the shale mass fraction increases to 30%—40%,obviously increasing 2—3 times;with an increase of distance from fault nuclear,shale mass fraction steady declines,which demonstrates that high gouge content is still one of the most important mechanisms in the fault of carbonate sequence;the differences of constitute and content of lithology lead to the disparity in strain form.Carbonate minerals,especially calcite is multistage,and crystal widely distributes in crushed zone,which indicates that the cementation is another important fault sealing mechanism.