断裂成因他源高压及其地质特征

Allogenic Overpressuring Associated with Faulting and Geological Consequences

开启断裂的活动造成其断开的渗透性地层之间的水动力连通 ,从而可在浅部地层产生极高超压。这种超压在形成机制、分布特征和识别标志等方面均与传统认识和讨论的类型大不相同。笔者等通过实例 ,分析了断裂成因他源高压的形成、分布及其对油气成藏的影响等。断裂连通系统中各渗透性地层内过剩压力完全一致 ,地层压力以静水压力梯度随深度增加 ;由构造应力或由地层压力为主导因素的断裂的形成对应着不同的压力形成机制、压力分布特征及演化过程 ;这类超压带之上的压力过渡带一般较薄 ,但受地层性质及超压形成后沉积速率的影响。这类高压的研究对于识别断裂活动、划分油气运聚单元、确定油气藏动力学过程、压力预测等均有重要意义。

Fault opening results in hydrodynamic connection among the high permeability reservoirs cut through by the faults. High overpressures caused by such connection are usually different from the traditionally discussed ones in mechanisms, pressure distribution, as well as their roles in hydrocarbon accumulation. The occurrence of the faulting induced allogenic overpressuring and the associated geological phenomena are analyzed, with demonstration of some examples from real basins. The occurrence process of faulting in overpressured rocks depends generally on the interrelationship among rock properties, tectonic stresses and overpressures. It is found that the pressures in reservoirs increase following the hydrostatic gradient in such a system, and that the faulting triggered by tectonic stress or overpressuring (resulting from other mechanisms) corresponds to different overpressuring processes and pressure distributions. The transition zone upon the overpressured zone is usually thin, and influenced by seals hydraulic properties as well as the deposition rate when alloginic pressuring occurs. The studies on this kind of overpressures are significant for identifying faulting activities, determining the domains of hydrocarbon systems, analyzing hydrocarbon accumulation and predicting pressure before drilling.