储层裂缝发育程度的判别准则

Evaluation criteria for development degree of micro cracks in oil and gas reservoir

实验研究表明 ,变形导致的岩石微破裂会使岩石产生扩容 (体积膨胀 )和非线性变形。当差应力达到岩石的屈服应力时 ,扩容和非线性应变开始。此外 ,随应力水平的增加 ,扩容和非线性变形呈幂函数形式增加。在围压低时 ,最大扩容量呈上升趋势 ,围压较高时呈下降趋势 ;非线性应变量随围压的增加而呈单调增加。这一结果可作为评价裂缝型油气藏裂缝发育密集程度的一种判别准则。与以往用破裂准则、应力和应变能大小等评价裂缝发育程度的方法相比 ,它更真实地反映了裂缝形成、扩展直至饱和阶段与应力的对应关系。扩容和非线性变形之间的差异在于扩容更偏重于张性裂缝 ,非线性变形更偏重于剪切裂缝。

The experimental results showed that micro cracks resulted from rock deformation could lead to volume dilatation and non-linear deformation of rock. The volume dilatation and the non-linear deformation of rock originated, when the differential stress equaled to the yield point of rock. Then, the volume dilatation and the non-linear deformation of rock increased exponentially with rising of the differential stress. The maximum volume dilatation increased firstly and then decreased with rising of confining pressure. The non-linear deformation of rock increases monotonously with rising of confining pressure. These results can be used as the criteria for estimating the condensed growth of micro cracks in oil reservoir. The evaluated results of this method accorded with the practical situation more than those of some methods usually used in oil reservoir evaluation, such as fracture criteria, stress level or strain energy level methods. There is a difference between volume dilatation and non-linear deformation of rock. The former relates more with tensional cracks, and the latter relates more with shear cracks.