上拱力背景下正断裂剖面形态及极限应力状态研究

THE INVESTIGATION OF NORMAL FAULT UNDER UPWELLING FORCE AND ITS CRITICAL STRESS STATE

上拱力构造背景下形成的正断裂及断裂极限应力状态研究在构造解释和油气运移成藏中具有重要的意义。在抛物线型莫尔包络线理论的基础上,通过合理的假设和数学推导以及理论模拟,进一步探讨上拱力构造背景影响下形成的正断裂剖面形态和断裂的极限应力状态,并定量给出函数表达式。研究结果表明,断裂在均质岩体中由浅到深,倾角从竖直开始由大变小,呈铲状断裂,而变化的速率只与地层物性有关,泥岩比砂岩变化快。断裂分布的深度与上拱力的大小成一次线性关系,上拱力越大,断裂分布越浅。砂泥岩互层地层中发育有典型的坡坪式正断裂。研究结果不仅与普遍认识相一致,而且可以进一步在实际应用中预测断裂的存在,定量解释断裂形态,求取上拱力和断裂极限应力状态。

The investigation of normal fault formed under tectonic setting of upwelling force and its critical stress state is of significance in the structural interpretation and the hydrocarbon migration. Based on the theory of parabolic Mohr failure envelope, and certain assumptions, mathematical derivation and theory modeling being carried out, quantitative functions of geometric shape of normal fault and its critical stress state were given. It is found that the fault dip becomes smaller from shallow to deep, being a listric fault. The rate of dip change is only related to the properties of strata. And the rate of dip change is faster in isotopic sandstone than in mudstone. It is also proved that the depth of the fault is linear against the amplitude of upwelling force. A typical ramp-flat normal fault can be drawn from the fracture modeling of interbedded sandstone-mudstone rock body. Not only are these conclusions consistent with the natural phenomena and general cognition, but also they can explain the geometric shape of faults quantitatively and find the critical stress state.