不同渗透率油藏储层应力敏感性实验研究

Experimental Study on the Stress Sensitivity in Different Permeability Reservoirs

为了探讨不同渗透率油藏储层应力敏感性的强弱,考虑低渗油藏储层裂缝发育的特征,利用巴西劈裂法室内实验研制含裂缝的储层物理模拟砂岩岩心,测试基质渗透率分别为18.876×10-3,234.247×10-3,540.12×10-3μm2的均质岩心和裂缝岩心在不同有效压力下的渗透率变化,结合渗透率保持率这一表征参数来分析裂缝对储层应力敏感性的影响,对低渗油藏与中、高渗油藏储层应力敏感性的差别进行了研究。结果表明:裂缝的存在大大增强了储层的应力敏感性。裂缝性油藏储层应力敏感性与裂缝的闭合程度有关,裂缝在低有效压力范围内未完全闭合,储层应力敏感性较强;有效压力超过一定范围后,裂缝完全闭合,储层应力敏感性减弱。不同渗透率下无裂缝均质油藏储层的应力敏感性相近,但在含有相同裂缝条件的油藏储层中,渗透率较低的油藏储层应力敏感性较弱;实际油藏条件下,裂缝多发育在低渗油藏储层中,因此表现为低渗油藏储层应力敏感性比中、高渗油藏储层应力敏感性强。

In order to study the stress sensitivity in different permeability reservoirs,the reservoir characteristics are considered,and the fractured cores with the matrix permeability of 18.876×10-3μm2,234.247×10-3μm2 and 540.12×10-3μm2 are made by the Brazilian test.The permeability of these homogeneous cores and fractured cores are tested at different effective pressures.The influence of fracture on the reservoir stress sensitivity is studied by the characterization parameter of permeability retention ratio.The stress sensitivity in low permeability reservoir and high permeability reservoir is compared.The results show that the fractures can enlarge the stress sensitivity of reservoirs.The stress sensitivity of reservoir is influenced by the closure degree of fractures,and the stress sensitivity is strong in low effective pressures because the fracture is not compacted completely,while the stress sensitivity is weak after the effective pressures beyond to a limitation as the fracture is closed totally.With the increasing permeability,the stress sensitivity of fractured reservoir improves evidently while the stress sensitivity of homogeneous reservoir remains stable.From the actual reservoir properties,the fractures always develop in the low permeability reservoir and few exist in the high permeability reservoir,so the stress sensitivity in low permeability reservoir is stronger than that in high permeability reservoir.