应力、应变与构造超压关系及构造超压控制因素分析

构造应力场引起岩石变形，并使孔隙流体压力发生变化，形成异常流体压力。根据对前人岩石力学实验结果的分析，应力与流体压力间为非线性关系，试件的体积应变与孔隙流体压力间为反相关线性关系。构造异常压力和其他异常压力的形成具有共性特征，都可以抽象为由于孔隙体积和流体体积的相对变化这一个因素。由此也可以将异常压力形成的一般过程概括为：孔隙疲充体饱和的岩石，体积缩小会使饱和流体排出，体积增大会使其周围的流体流入，如果渗透率足够大，流体流动顺畅，这一过程流体压力的变化相对较小。在岩石渗透率较小时，由于流量的限制，流体在这一过程中会产生明显的压力变化，形成异常压力。对于符合达西渗流的流体，异常压力计算时，流量可以用孔隙体积相对变化量替代。这样可以描述构造变形等固体变形所引起的异常压力。根据异常压力的极大值为研究区相应深度的最小主应力和岩石抗张强度之和的特点，可以预测流体封存箱箱壁的最小厚度要求，分析流体封存箱形成的基本条件。构造活动过程中，岩石孔隙的体积应变速率和封存箱壁的渗透率直接控制异常流体压力的大小。高应变速率和低的封存箱壁渗透率是形成构造超压的主要因素。

Relationship of Stress & Strain to Abnormal Tectonic Pressure and Main Control Aspects on Abnormal Tectonic Pressure Forming

Tectonic stress can cause the deformation of rocks as well as the change of fluid pressure in the pore of rocks forming anomaly tectonic fluid pressure. Through analysis of the lithomechanical experiment results of Paterson etc, the authors find that the stress has a non-linear relationship to anomaly fluid pressure, while the volume strain has a linear relationship to anomaly fluid pressure. The anomaly pressures formed by other mechanisms all have the same characters - the relative changes of pore volume and fluid volume in the pore. So the general process of anomaly pressure formed by different mechanisms: when the rocks that have been saturated by fluid, the relative reduction of the pore volume causes the expelling of fluid; and the relative enlargement of the pore volume causes the inflow of fluid. If the permeability of the surrounding rocks is large enough, there would be no obvious anomaly fluid pressure formed. In contrast, if the permeability of surrounding rocks is small, the anomaly fluid pressure will be formed. The thickness and permeability of surrounding rocks and the strain rate of the pore are the main factors for forming anomaly pressure.