论文部分内容阅读
阐述了高孔隙压力单独作用能产生天然水力裂隙、并使之保持一段很长时间张启的机理。这样的裂隙可以出现在张性、中性或压性构造背景下。尽管裂隙的方向由区域应力场控制,但在水平应力差不足以引起区域性拉张时,裂隙仍可以产生并保持张启。更确切地说,这些裂隙是寄主岩石的固体组分(颗粒)收缩的结果。这样,由孔隙压力增加引起的颗粒收缩就类似于由温度降低引起的颗粒收缩,也能在岩石中产生张性裂隙。此裂隙称为水力收缩裂隙,以区别于其它类型的水力裂隙,如由侵入流体而不是孔隙流体产生的水力裂隙。用简单的计算来说明这类裂隙产生的理论基础,并用不同的例子来解释裂隙产生的可能性与方向是如何受到寄主岩石的力学性质和不同的地质作用过程的影响。这些例子表明孔隙压力的大小不能单独作为产生裂隙的判别标准。裂隙产生的可能性与方向取决于导致孔隙压力的地质作用和裂隙产生前岩石的力学属性。一般而言,垂向(收缩)裂隙倾向于、也应该产生于低孔隙压力下,埋藏在低地温梯度盆地、压缩性较差的岩石之中。
The mechanism that high pore pressure alone can produce natural hydraulic fractures and maintain it for a long time is expounded. Such fissures can occur in the tensional, neutral or compressional tectonic setting. Although the direction of fractures is controlled by the regional stress field, the fractures can still produce and maintain the tension when the horizontal stress difference is not enough to cause regional tension. Rather, these fissures are the result of shrinkage of the solid components (particles) of the host rock. In this way, the contraction of the particles caused by the increase in pore pressure is similar to the contraction of the particles caused by a decrease in temperature, and the generation of tensile cracks in the rock. This fissure is called a hydraulic shrinkage fissure to distinguish it from other types of hydraulic fissures, such as hydraulic fissures created by intrusive fluids rather than pore fluids. A simple calculation is used to illustrate the theoretical basis for the generation of such fractures. Different examples are used to explain how the possibility and direction of fractures are affected by the mechanical properties of the host rock and the different geological processes. These examples show that the magnitude of pore pressure alone can not be used as a criterion for the fracture. The possibility and direction of fissure generation depends on the geological effects that lead to pore pressure and the mechanical properties of the rock before fissure production. In general, vertical (shrinkage) fractures tend to, and should also occur under low pore pressure, buried in rocks of poorly compressible nature in low-geothermal gradient basins.