低渗透薄互层砂岩油藏大型压裂裂缝扩展模拟

SIMULATION OF FRACTURE PROPAGATION IN LARGE-SCALE RESERVOIR WITH LOW PERMEABILITY AND THIN INTERBEDDED SANDSTONE

对低渗透薄互层砂岩油藏的大型压裂开发时,由于低渗透薄互层砂岩油藏中隔层岩层比较薄、强度低,对裂缝高度方向上的扩展抑制作用较小,往往会出现裂缝长度与高度之比小于4,导致只考虑缝内流体一维流动的拟三维裂缝扩展模型不再适用。根据低渗透薄互层砂岩油藏大型压裂的特点,在适当假设的基础上,应用线弹性断裂理论,建立考虑缝内流体沿着裂缝高度和长度方向流动的拟三维裂缝扩展模型,并用解析法得到压裂过程中裂缝扩展尺寸和缝内流体压力的精确解;利用VisualBasic计算机语言编制二维流动的拟三维裂缝扩展模型求解程序,并对某低渗透薄互层砂岩油藏压裂过程中裂缝扩展情况进行了求解分析。计算结果表明:二维流动的拟三维裂缝扩展模型能够很好地预测低渗透薄互层砂岩油藏大型压裂过程中裂缝的扩展,可以满足工程需求。

The length/height ratio of fracture is usually smaller than 4. When the large-scale hydraulic fracturing is carried out on reservoir with low permeability and thin interbedded sandstone, because the interlayer is thin and its strength is low, a weak restriction is shown in the height of fracture development. Under this condition, the pseudo-3D model only considering the fluid flowing along the length direction of fracture does not work. So, the pseudo-3D model of predicting the fracture development with 2D flow is built up according to the characteristics of hydraulic fracturing in reservoir with low permeability and thin interbedded sandstone based on linear elastic fracture theory and proper hypotheses. The precise solutions of fracture length and height are calculated by the pseudo-3D model during hydraulic fracturing. The program for fracture parameters is coded based on the pseudo-3D model of 2D flow, which is used to simulate the fracture development during hydraulic fracturing in an actual reservoir with low permeability and thin interbedded sandstone. The results show that the pseudo-3D model of 2D flow has a perfect performance in analyzing the fracture development during large-scale hydraulic fracturing in reservoir with low permeability and thin interbedded sandstone, and can be satisfied with engineering demands.