气体管流到达西流的缝高界限实验测试与理论计算

Experimental test and theoretical calculation of the fracture height limit of gas pipe flow to Darcy flow

采用超细铜管模拟碳酸盐岩地层中微裂缝,开展低速流动实验,分析气体在不同缝高裂缝中的流动状态变化,确定流动状态转换界限及转换区间,建立流动状态转换界限计算方法。研究表明,气体在缝高较大裂缝中的流动形式以理想的哈根-泊肃叶流动为主。由于缝高的减小,气体在裂缝中的流动从以理想光滑缝面的哈根-泊肃叶流动为主向非哈根-泊肃叶流动为主转换,转换的临界点即为流动状态转换界限。裂缝缝高在流动状态转换缝高界限以下继续减小到一定程度后,气体流动形式逐渐向理想的达西流动转换,从而可以确定裂缝在闭合过程中流动状态的转换区间。综合裂缝面的三维微凸体扫描结果、裂缝的材料性质及流体性质,建立了流动状态转换界限计算方法。实验测试和理论计算表明:从管流到达西流的缝高界限约为裂缝上、下两面微凸体最大高度之和的2倍。

Low-speed flow experiments in which ultra-fine copper tubes are used to simulate micro-fractures in carbonate strata are conducted to analyze the variations of gas flow state in fractures of different fracture heights,determine flow state transition limit and transition interval,and establish the calculation method of flow state transition limit.The results show that the ideal Hagen-Poiseuille flow is the main form of gas flow in large fractures.Due to the decrease of fracture height,the gas flow in the fracture changes from Hagen-Poiseuille flow with ideal smooth seam surface to non-Hagen-Poiseuille flow,and the critical point of the transition is the boundary of flow state transition.After the fracture height continues to decrease to a certain extent below the boundary of the flow state transition fracture height,the form of gas flow gradually changes to the ideal Darcy flow,thus the transition interval of the gas flow state in the closing process of fracture can be determined.Based on the three-dimensional microconvex body scanning of the fracture surface,the material properties of fracture and properties of fluid in the fracture,a method for calculating the boundary of flow state transition is established.The experimental test and theoretical calculation show that the limit of the fracture height for the transition from pipe flow to Darcy flow is about twice the sum of the maximum height of the microconvex bodies on the upper and lower sides of the fracture.