力学学报 ›› 2017, Vol. 49 ›› Issue (4): 828-835.doi: 10.6052/0459-1879-17-034

• 流体力学 • 上一篇    下一篇

低渗透煤层气藏中气-水两相不稳定渗流动态分析

刘文超1, 刘曰武2   

  1. 1. 北京科技大学土木与资源工程学院, 北京 100083;
    2. 中国科学院力学研究所, 北京 100190
  • 收稿日期:2017-01-10 出版日期:2017-07-15 发布日期:2017-08-01
  • 通讯作者: 刘文超,讲师,主要研究方向:渗流力学.E-mail:wcliu 2008@126.com;刘曰武,研究员,主要研究方向:渗流力学.E-mail:lywu@imech.ac.cn E-mail:wcliu 2008@126.com;lywu@imech.ac.cn
  • 基金资助:

    国家自然科学基金(51404232)、中国博士后基金(2014M561074)和国家科技重大专项(2011ZX05038003)资助项目

DYNAMIC ANALYSIS ON GAS-WATER TWO-PHASE UNSTEADY SEEPAGE FLOW IN LOW-PERMEABLE COALBED GAS RESERVOIRS

Liu Wenchao1, Liu Yuewu2   

  1. 1. School of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing 100083, China;
    2. Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
  • Received:2017-01-10 Online:2017-07-15 Published:2017-08-01
  • Contact: O357.3 E-mail:wcliu 2008@126.com;lywu@imech.ac.cn

摘要:

针对低渗透煤层渗流问题,考虑启动压力梯度及其引起的动边界和动边界内吸附气解吸作用的渗流模型研究目前仅限于单相流,而更符合实际的气-水两相渗流动边界模型未见报道.本文综合考虑了煤层吸附气的解吸作用、气-水两相渗流、非达西渗流、地层应力敏感等影响因素,进行了低渗透煤层的气-水两相渗流模型研究.采用了试井技术中的“分相处理”方法,修正了两相渗流的综合压缩系数和流度,并基于含气饱和度呈线性递减分布的假设,建立了煤层气藏的气-水两相渗流耦合模型.该数学模型不仅可以描述由于低渗透煤层中渗流存在启动压力梯度而产生的可表征煤层有效动用范围随时间变化的移动边界,还可以描述煤层有效动用范围内吸附气的解吸现象以及吸附气解吸作用所引起的煤层含气饱和度的上升;为了提高模型精度,控制方程还保留了二次压力梯度项.采用了稳定的全隐式有限差分方法进行了模型的数值求解,并验证了数值计算方法的正确性,获得了模型关于瞬时井底压力与压力导数响应的双对数特征曲线,由此分析了各渗流参数的敏感性影响.本文研究结果可为低渗透煤层气藏开发的气-水两相流试井技术提供渗流力学的理论基础.

关键词:

煤层气|启动压力梯度|吸附气解吸|动边界|两相流|有限差分方法

Abstract:

At present, the research on the seepage flow models in low-permeable coalbeds is only limited to the single phase flow cases, which simultaneously considerate the existence of threshold pressure gradient in the seepage flow process, its produced moving boundary and the desorption function of adsorbed gas inside the moving boundary; however, the research on the gas and water two-phase seepage models with moving boundaries, which are more consistent with the actual situations, has not been reported yet. In comprehensive consideration of these influential factors including the desorption function of the adsorbed gas in coalbeds, gas-water two-phase seepage flow, the non-Darcy seepage flow characteristics in the low-permeable formations, the stress-sensitive effect of the formation, etc., modeling the gas-water two-phase seepage flow in low-permeable coalbeds is studied in this paper. According to the "phase separation" method involved in the well testing technology, both the comprehensive compressibility coefficient and the fluidity are modified for the two-phase seepage flow problem; and then based on the assumption of the linear spatial distribution of the gas saturation, a coupled model of gas-water two-phase seepage flow in low-permeable coalbeds is built. The mathematical model can not only depict the moving boundary that represents the change of the effectively disturbed coalbed area with time due to the existence of threshold pressure gradient in the seepage flow process in low-permeable coalbeds, but also can depict the desorption phenomena of the adsorbed gas in the effectively disturbed coalbed area, and the increase of the gas saturation in coalbeds caused by the desorption function of the adsorbed gas; furthermore, in order to improve the accuracy of the model, the quadratic pressure gradient term is retained in the governing equation of the model. A fully implicit finite difference method is adopted to numerically solve the model, and the correctness of the numerical method is also verified. Eventually, the log-log type curves regarding the transient wellbore pressure response and its derivative are obtained from the model, and then the sensitive-effects of some seepage flow parameters can be analyzed. The presented research results in the paper can provide theoretical foundations of seepage flow mechanics for the well testing technology for the gas-water two-phase seepage flow in the development of low-permeable coalbed gas reservoirs.

Key words:

coalbed methane|threshold pressure gradient|desorption of the absorbed gas|moving boundary|two-phase flow|finite difference method

中图分类号: 

  • O357.3