考虑压力拱效应的应力敏感实验

 低渗储层一般具有较强的应力敏感性,目前进行应力敏感实验研究时,均假设上覆压力不变。事实上,油气开采时,上覆岩层中会产生压力拱效应,作用于储层的上覆压力减少,从而影响应力敏感实验结果。以压力拱理论为基础,计算了苏里格气田不同形状储层的压力拱比,确立了苏里格气田气藏开采时的上覆压力和有效应力表达式,首次将该理论应用于应力敏感实验。得到了苏里格气田不同形状储层以及不同渗透率级别条件下的应力敏感特征。结果表明,苏里格近椭圆柱体储层和近饼形储层的压力拱比分别为0.12和0.28,与常规应力敏感实验相比,考虑压力拱效应时,测试渗透率高于常规实验渗透率,应力敏感程度降低。流体压力降低25MPa,初始渗透率≤0.1mD的低渗致密储层,压力拱比分别为0.12和0.28时,对应的渗透率分别为常规应力敏感实验渗透率的1.2和1.5倍;初始渗透率在10~50mD,压力拱比分别为0.12和0.28时,对应的渗透率分别为常规实验渗透率的1.01和1.02倍。低渗透储层受压力拱的影响程度大于高渗储层。

Stress Sensitivity Experiment under Consideration of Stress Arching Effect

Low Permeability reservoir is quite sensible to the effective stress. Current all sensitive experiments suppose that the overburden pressure is a constant during the production. Actually, during oil and gas exploitation, a stress arching effect comes into play in the overburden, reducing the overburden pressure acting on the reservoir. Based on the theory of the stress arching, the stress-to-arching ratio, overburden pressure, and effective stress expression in Su Lige gas field are calculated. It is the first time that the theory is applied to the stress sensitive experiments. The experiments take the reservoir shape and different range of initial permeability into consideration. The results show that the stress-to-arching ratios are 0.12 and 0.28, respectively for the elliptic cylinder reservoir and penny-shaped reservoir in Su Lige gas field. Comparing with the conventional experiments, under the same condition, the measured permeability is usually higher and the degree of the sensitivity is smaller. When the pressure drops 25MPa, for the stress-arching-ratios of 0.12 and 0.28, the measured permeability are 1.2 and 1.5 times of the permeability value obtained by conventional experiments for the reservoir with low permeability, which initial permeability is smaller than 0.1mD. However, when the initial permeability is between 10mD and 50mD and stress-to-arch ratios are 0.12 and 0.28, respectively, the corresponding permeability are 1.01 and 1.02 times of the permeability got by the conventional experiments. The low permeability gas reservoir is more sensitive to the stress arching than the high permeability gas reservoir.