微裂缝性特低渗透油藏储层特征研究

将不同渗透率的含微裂缝与相同渗透率、不含微裂缝低渗透砂岩岩心进行了对比,研究了微裂缝性特低渗透油藏的孔隙空间形态、喉道半径、微观均质系数和相对分选系数等特征,分析了这些特征对孔隙度渗透率性质、可动流体体积和压力敏感性等方面的影响。结果表明,微裂缝性特低渗透砂岩孔道与孔道之间主要靠微裂缝连接,连通性较低,主要由微裂缝提供渗流能力。气测渗透率和微裂缝宽度、微观均质系数、相对分选系数和可动流体体积百分数等都有明显的幂律关系。孔隙度与渗透率相关性差,气测渗透率与水测渗透率比值较大,各向异性和非均质性严重,压力敏感性较强。渗透率低不是低渗透油藏的本质特征,只是外在表现形式之一。应该根据微观孔隙结构特征、可动流体体积百分数和压力敏感特征等多个因素综合评价其储层特征。

Reservoir characteristics of micro-fractured ultra-low permeability reservoirs

The features of pore space, throat radius, microcosmic uniformity coefficient and relative sorting coefficient of micro-fractured ultra-low permeability reservoir were compared with those of non-fractured ultra-low permeability reservoir under the condition of same permeability. The effects of porous microstructure features on porosity and permeability,volume percentage of mobile fluid and pressure sensitivity were also analyzed. The results showed that the throats of micro-fractured ultra-low permeability cores were connected each other mainly by micro-fractures,and the communication of throats was lower. The micro-fractures had the essential contributions to the micro-fractured ultra-low permeability reservoirs during the flow event. The permeability of reservoirs was correlated tightly with the width of micro-fracture, microcosmic uniformity coefficient,sorting coefficient and volume percentage of mobile fluid in the power law equation. The relationship between porosity and permeability was poor;and the ratio of permeability measured by gas to the permeability measured by water was larger. The heterogeneity,anisotropy and pressure-sensitive effect were all strong. The lower permeability is one of the apparent characteristics of low-permeability reservoirs. The reservoir characteristics of low permeability reservoirs should be synthetically evaluated on the basis of microstructure features of pores, volume percentage of mobile fluid and pressure-sensitive effect.