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页岩气层自支撑裂缝气−水流动规律试验研究

Experimental study on two-phase gas-water flow in self-supported fractures of shale gas reservoir

  • 摘要: 为探究页岩气层自支撑裂缝气−水流动规律, 以四川盆地龙马溪组页岩为研究对象, 开展了不同围压作用下页岩垂直和平行层理自支撑裂缝的气−水两相渗流试验。试验结果表明: 页岩裂缝表面凸起高度呈高斯分布, 随着自支撑裂缝表面凸起数量及高度的增加, 等效缝宽和气/水绝对渗透率呈增加趋势; 垂直层理裂缝表面粗糙程度高于平行层理裂缝, 导致垂直层理裂缝导流能力普遍高于平行层理裂缝; 相较于拉张型裂缝, 垂直层理剪切型裂缝绝对渗透率升高了3~10倍, 平行层理剪切型裂缝绝对渗透率升高了2~4倍; 水相流体相对渗透率与水相分流量正相关, 水相分流量较高时, 水相受到围压以及裂缝表面形貌的影响明显高于气相, 裂缝等渗点相对渗透率随着围压升高而降低, 随着粗糙度升高而降低。相较于拉张型裂缝, 剪切型裂缝内相间阻力降低, 水相相对渗透率相较气相升高更加明显, 等渗点水相分流量未发生明显变化, 垂直层理剪切型裂缝等渗点相对渗透率升高1.39~1.71倍, 平行层理剪切型裂缝等渗点相对渗透率升高1.02~1.39倍。研究认识对于指导考虑自支撑缝网导流能力保护的页岩气井控压生产制度优化具有重要意义。

     

    Abstract: Shale self-supporting fracture serves as an important junction connecting matrix and artificial fractures, however, the gas-water flow behavior of the production process remains unclear. Experiment on the gas-water seepage behavior of vertical/parallel bedded self-supported fractures under stress was carried out on Longmaxi Formation shale in the Sichuan Basin. The study shows that the height of shale fracture surface convexities conforms to Gaussian distribution. With the increase of the number and height of the fracture surface convexities, the equivalent aperture and absolute gas/water permeability tend to increase. The surface roughness of vertical-bedding fractures was higher than that of parallel- bedding fractures, resulting in a generally higher conductivity of vertical-bedding fractures than that of parallel-laminated fractures. Compared with tensile fractures, the absolute permeability of vertical-bedding shear fractures increased 3-10 times, and the absolute permeability of parallel-bedding shear fractures increased 2-4 times. In the two-phase gas-water flow condition, the relative permeability of water-phase was positively correlated with the fractional flow of water phase. With the higher fractional flow of water, the water phase was affectd more significantly by the confining pressure and the surface morphology than that of gas phase, and the relative permeability of equal permeability point increased with the increase of the confining pressure, and decreased with the increase of the roughness. Compared with the tensile fractures, the two-phase fluid flow resistance decreased, and the relative permeability of the water phase rised more obviously than that of the gas phase, and the fractional flow of water phase at equal permeability point did not change significantly, the relative permeability of equal permeability point of the vertical-bedding shear fracture increased 1.39 to 1.71 times, and that of equal permeability point of the parallel-bedding shear fracture increased 1.02 to 1.39 times. The results are of great significance in guiding the optimization of pressure-controlled production system when considering the protection of conductivity of self-supporting fracture networks in shale gas wells.

     

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