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Experimental Study on the Influence of Slippage Effect on Threshold Pressure Gradient in Low Permeability Gas Reservoir
DOI: 10.12677/APF.2018.82003, PDF, HTML, XML, 下载: 1,176  浏览: 2,559

Abstract: Gas seepage in dense porous media, threshold pressure gradient and slippage effect exist at the same time. In order to study the effect of slippage effect on the threshold pressure gradient in low permeability gas reservoir, based on the percolation theory, this paper adopts the experimental methodology to study the coal samples in Wangying coal mine in order to conduct seepage test. By the test data fitting, the slippage factor of threshold pressure gradient and slippage effect is obtained respectively. The results show that as the slippage factor increases, the threshold pressure gradient decreases gradually, and there is a good linear negative correlation with the slippage factor. It is indicated that the more obvious the slippage effect is, the more favorable the flow of gas is, and thus the pressure gradient will be reduced. So it is of guiding significance to establish the test model of slippage factor-threshold pressure gradient for improving the mining of coal bed methane.

1. 引言

2. 低渗气藏渗流试验

2.1. 试验目的

2.2. 试验材料及方法

$k=\frac{Q\mu \Delta L}{A\Delta P}$ (1)

3. 试验结果分析

3.1. 低渗透气藏启动压力梯度试验数据拟合分析

Figure 1. Experiment program

Figure 2. Pressure gradient effect under different confining pressures

$\nu =\left\{\begin{array}{l}0,|\nabla p|\le G\\ -\frac{k}{\mu }\nabla p\left(1-G/|\nabla P|\right),|\nabla p|>G\end{array}$ (2)

3.2. 低渗气藏滑脱效应试验数据拟合分析

$k=\frac{2{p}_{0}Q\mu L}{A\left({P}_{1}^{2}-{P}_{2}^{2}\right)}$ (3)

(a) 围压5 MPa (b) 围压8.5 MPa (c) 围压12 MPa (d) 围压15 MPa

Figure 3. Threshold pressure gradient under different confining pressures

4. 讨论

$\lambda =A+Bb$

Figure 4. Gas slippage effect under different confining pressures

Figure 5. The relationship between the slippage factor and the threshold pressure gradient

Table 1. The date of slippage factor and threshold pressure gradient

5. 结论

1) 低渗气藏气体的渗流流动存在启动压力梯度，并且随着围压的增大，启动压力梯度增大。

2) 低渗气藏渗流的滑脱效应是普遍存在的，低压条件下，随着孔隙压力的增大，滑脱效应比较明显；但随着围压的增大，滑脱效应的影响逐渐减弱。

3) 在一定的围压范围内，滑脱因子与启动压力梯度呈现很好的线性递减关系，滑脱效应的存在有利于减小启动压力梯度，更加有利于煤层气的开采。

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