低渗透储层原位条件下应力敏感性评价

Evaluation on Stress Sensibility of Low Reservoir in Situ Conditions

为探讨围压和孔隙压力对岩石渗透率的影响及岩石渗透率敏感性评价的新方法,选取松辽盆地3块低渗透储层岩样,采用岩石伺服三轴实验系统,分别做常规条件和原位条件下的应力敏感性评价,得到三方面结果。1)3块样品的渗透率随围压增大而降低,随着孔隙压力的增大而增大。2)原位条件下,物性越差的样品储层应力敏感性越强。借助扫描电子显微镜和恒速压汞实验,解释了低渗透储层敏感性差异存在的机理。储层岩石喉道的大小和形态、黏土含量和类型、矿物胶结程度是决定渗透率敏感性差异的原因。3)塑性矿物含量和类型是决定渗透率敏感性差异的主要因素,即云母、黏土等塑性矿物含量越高,致密岩石储层渗透率应力敏感性越强。在实际工作中,评价岩石渗透率敏感性时一般只考虑围压单因素的影响,会对评价结果带来较大的人为误差,而岩样地层所处的孔隙压力等条件对渗透率影响不容忽视。为准确地认识低渗透储层的应力敏感特征,制定更合理的生产压差,建议进行岩样渗透率敏感性评价时,恢复地下原位条件。

In order to study the effect of confining press and pore press on permeability, the new method of evaluation on stress sensibility is proposed. Three pieces of low permeable reservoir rock samples in Songliao Basin are selected. A servo-controlled triaxial rock mechanics test system is employed to investigate the permeability of sandstone samples under conventional conditions and in situ conditions. The results show that： 1） The permeability of three pieces of samples reduce with confining press increasing and pore press reducing. 2） The denser the rock is, the stronger stress sensitivity is, in situ conditions, which explains the mechanism of low permeability reservoir sensitivity differences by means of X-ray diffraction（XRD）, scanning electron microscopy（SEM）, constant speed mercury injection experiment. What＇s more, throat size and shape, plastic mineral content and type contribute to the differences of permeability sensitivity. 3） Mineral content and type of plastic are the major factor of the sensitivity of permeability differences. The stress sensitivity of tight reservoir permeability rock becomes strong with the increasement of mica, clay and other plastic mineral content. In the practical work, evaluation on stress sensitivity of permeability, the effect of confining pressure single factor is mostly considered, butthe effect pore presss would be ignored, which is bound to bring larger human error. So evaluation on stress sensibility in situ conditions is essential, which is significant for further understanding of stress sensitivity of low permeability reservoir characteristics and development.