Biot相恰理论在砂泥岩地层裂隙评价中的应用

The Application of Micro Fracture in Sand Shale Formation Using Biot-consistent theory

以相对浅层砂泥岩地层及深层致密砂岩储层为例,利用Biot相恰理论计算了地层中裂隙密度ε分布,探讨了总孔隙度、裂缝孔隙度、波速、应力环境及岩石体积模量与裂隙密度间的关系.结果表明,微裂隙随应力环境的增加而产生.相对浅层砂泥岩地层和深层致密砂岩储层类似,岩石孔隙度与波速间负相关;对于深层致密砂岩储层而言,若地层不存在超压,则高应力环境往往导致微裂隙的闭合,超压能抵消部分环境应力,对孔裂隙的张开起一定促进作用.裂隙密度ε反演结果表明,两类地层裂隙密度均与地层裂缝孔隙度具有较好正相关性,但由于裂隙空间相对较小,所占空间份额有限,随着裂隙密度的增加,地层裂缝孔隙度逐渐趋向于一个极值.岩石体积模量随裂隙密度增加而减小,裂隙密度与岩石物性、古今应力环境等方面因素密切相关.

In this paper, we make the relatively shallow sand shale formation and the deep tight sandstone reservoir as example,calculate the crack density distribution using Biot- consistent theory, discussed the relationship of total porosity, fracture porosity,wave velocity, stress environment, rock bulk modulus and fracture density. It shows, the micro cracks appear with the increase of stress environment. It＇s similar for the relatively shallow sand shale formation and the deep tight sandstone reservoir, there＇s negative relation for the rock porosity and the wave velocity; for the deep tight sandstone reservoir, if it is not overpressure, the high stress environment often leads to the closing of microcracks, the overpressure can offset part of the environmental stress, it has a certain promoting effect for the open of the pore fissure. Inversion results of fracture density shows that, density shows of both strata have good positive correlation with formation fracture porosity, but due to the fracture space is relatively small, with the increase of fracture density, the formation fracture porosity gradually achieve an extreme value. With the increase of fracture density, the rock bulk modulus decreases, there ＇ s a close relationship of fracture density and potrophysical and ancient and modern stress environment.