页岩气缝网优化的数值模拟

Optimized numerical simulation of the fracture network in the shale gas

为定量评价页岩气储层压裂缝网参数对产量的影响程度,运用页岩渗流机理,通过Eclipse建立页岩气水平井压裂后形成的复杂缝网模型,进行局部网格加密,分析了改变单因素(段间距、簇数、簇间距、次生缝间距、主缝长、次生缝长、主缝导流能力、次生缝导流能力、天然裂缝渗透率)对累计产量的影响,再对所有参数进行多因素正交方案设计,找出影响累计产气量的主控因素先后顺序并得到产量最大化的方案。结果表明,随着段间距、簇数与簇间距的增加,累计产气量随之减少;随着主缝与次生缝的长度增加,累计产气量随之增加;随着天然裂缝渗透率的增加,累计产气量随之增加;影响累计产气量的第一因素是天然裂缝渗透率,排在2到5位的依次是段间距、主缝长、簇间距与簇数,其他4个因素对累计产气量影响不大;正交方案设计中累计产量最多的方案为段间距40m,3簇,簇间距40m,次生缝间距30m,主缝长530m,次生缝长40m,主缝导流能力7×10-3μm2·m,次生缝导流能力2×10-3μm2·m,天然裂缝渗透率0.0008×10-3μm2,累计产量为2.94×108m3。在实际生产中,尽可能提高主裂缝长度,压缩段间距、簇间距与簇数对页岩气产量有较大的提升。研究结果为页岩气压裂缝网部署提供了参考。

In order to quantitatively evaluate the influenced degree of the fracture network parameters of shale-gas reservoir fracturing on the production, with the help of the shale flow mechanism and Eclipse, the complex fracture network mode was established after fracturing of the horizontal well, the local grid refinement was conducted, the influences of changing the single-factor(segment/interval spacing, branch number and interval, secondary fracture spacing, primary and secondary fracture lengths, primary and secondary fracture conductivities, natural fracture permeability) on the cumulative production were analyzed, and then multi-factor orthogonal program design was engaged for all the parameters to find out the sequence of the primary controlling factor to the cumulative production and obtain the maximized program of the production. The results show that with the increase of the segment spacing, branch number and interval, the cumulative production declines on the contrary;with the rise of the lengths of the primary and secondary fracture, the cumulative production grows up as well;with the increase of the permeability of the natural fracture, so as the cumulative production. The first influencing factor to the cumulative production is the permeability of the natural fracture, the next is the segment spacing, length of primary fracture, branch spacing and interval;in the orthogonal program design, the largest cumulative production is that when the segment spacing is 40 m, the branches are three, the branch spacing is 40 m, the secondary fracture spacing is 30 m, the length of the primary fracture is 530 m, the length of the secondary fracture is 40 m, the conductivity of the primary fracture is 7×10 -3 μm2·m, the conductivity of the secondary fracture is2×10 -3 μm2·m and the permeability of the natural fracture is 0.000 8×10 -3 μm2, the cumulative production is2.94×10 8 m 3. In the actual production, the length of the primary fracture should be enhanced as much as possible, while for the segment and branch intervals, and furthermore the branch number, they are just on the contrary, thus the production of the shale gas can be greatly increased. The research results can provide the reference for the arrangement of the shale-gas fractured grid.