断层连通概率法定量评价断层的启闭性

以大港油田埕北断阶带控烃断层上、下盘储集层内油气存在与否作为判别断层启闭性的指标,综合考虑多种因素的影响,提出了一种定量评价断层启闭特征的新方法--断层连通概率法.此法将影响断层启闭性的主要因素归结为泥岩流体压力、断面正应力和泥岩涂抹3个代表性参数,依据其影响断层启闭性的机理构建出一个无量纲的断层启闭系数.在此基础上,选取横切断层的典型油气藏剖面,计算断面不同位置处的启闭系数,根据其上、下两盘储层内是否含油来确定其"开启"或"封闭"性质.通过概率统计分析所建立的断层启闭系数与断层连通概率间的相关关系表明,当断层启闭系数小于1.0时,断层连通概率为0;启闭系数为1.0～3.5时,二者关系可表达为一个二次多项式;当启闭系数大于3.5时,断层连通概率为100%.由此在拓扑展开的断层面上勾绘出连通概率等值线,展现出断层面不同位置处的启闭性特征.

Quantitative evaluation of fault sealing property with fault connectivity probabilistic method

A new quantitative method for evaluating fault sealing properties based on fault connectivity probability is proposed by taking the occurrence of oil and gas in footwall and hangingwall reservoirs of hydrocarbon controlling faults in Chengbei falut step zone of Dagang oilfield as the index of identifying the sealing properties of faults and by taking into consideration many factors that have influence over the properties. Three parameters, i.e. fluid pressure of mudstone, normal stress on fault plane, and clay smear, are regarded as the major factors that influence the sealing properties of faults, and a dimensionless sealing coefficient is defined according to the mechanisms of their influence over the sealing properties of faults. Then typical reservoir profiles crossing faults are selected to calculate sealing coefficients on different parts of the profile and the sealing properties of faults are determined according to the occurrence of oil in the footwall and hanging wall. Furthermore, statistical analysis of the relationship between the sealing coefficients and fault connectivity probability shows that when the coefficient is less than 1. 0, the connectivity probability is naught ; when the coefficient ranges from 1.0 to 3.5, the relationship between them can be expressed by a quadratic equation; and when the coefficient is more than 3.5, the connectivity probability equals 100%. The connectivity probability contour on a strike projection reveals the sealing properties of different parts on the fault plane.