A dynamic predictive permeability model in coal reservoirs: Effects of shrinkage behavior caused by water desorption
A dynamic predictive permeability model in coal reservoirs: Effects of shrinkage behavior caused by water desorption
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DOI：
10.1016/j.petrol.2018.05.028
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发表时间：
2018-09-01
影响因子：
--
通讯作者：
Lin, Wenji
中科院分区：
文献类型：
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作者：
Miao, Yanan;Li, Xiangfang;Lin, Wenji
准确预测煤储层的产量越来越受到业界的关注。煤储层渗透率是影响煤层气产量的关键参数。从现有文献来看，煤渗透率的动态变化主要取决于有效应力、瓦斯解吸引起的煤基质收缩以及煤层井排水过程中瓦斯滑移的影响。煤基质中水所占的体积被忽视，其对基质解吸收缩效应的影响尚未被研究。本文在S-D应力-渗透率模型的基础上(Shi和Durucan，2004)，建立了充分考虑有效应力、瓦斯解吸引起的煤基质收缩、瓦斯滑移和水解吸引起的煤基质收缩影响的煤渗透率动态预测模型。揭示了煤层气开发过程中渗透率的动态变化。通过与实验结果的良好一致性，成功验证了所提出的渗透率变化模型的可靠性。此外，常用模型和新模型之间的比较表明，新模型的预测渗透率比其他模型（例如 P-M、S-D 和 C-B 模型）被高估。新模型与传统模型的巨大差异，凸显了考虑水分解吸引起的基质收缩对煤渗透率影响的必要性和意义，不容忽视。此外，基于所提出的渗透率模型，煤基质中相对湿度的影响受到了重视。对比分析了四种对煤层气井动态渗透率的影响。结果表明，相对湿度对煤的渗透性能有重要影响，会增加煤储层的动态渗透率。因此，水解吸引起的煤基质收缩效应将增加煤储层的动态渗透率。瓦斯滑移对煤储层动态渗透率影响较小。
Forecasting production in coal reservoirs accurately has been of growing interest in the industry. Permeability of coal reservoirs is a key parameter affecting coalbed methane production. In terms of current literature, the dynamic variation of coal permeability mainly depends on the effect of effective stress, coal matrix shrinkage caused by gas desorption and gas slippage during coalbed well drainage. The volume occupied by water in coal matrix was overlooked and its effect on matrix desorption-shrinkage-effect has not been investigated ever. In this work, on the basis of S-D stress-permeability model (Shi and Durucan, 2004), a dynamic prediction model of coal permeability fully considering the effect of effective stress, coal matrix shrinkage caused by gas desorption, gas slippage and coal matrix shrinkage caused by water desorption was established. The dynamic variation of permeability in coalbed methane development was revealed. The reliability of proposed model for permeability variation was successfully verified through the excellent agreements compared with experimental results. In addition, comparisons among the commonly utilized models and the new model indicated that the predicted permeability from the new model is overestimated than other models, such as P-M, S-D, and C-B models. The large differences between the new model and traditional models explicitly stress the necessity and significance of considering the matrix shrinkage effect caused by water desorption on coal permeability, which should not be neglected. Furthermore, based on the proposed permeability model, the influence of relative humidity in coal matrix was seriously paid attention. The four effects for the dynamic permeability of coalbed methane well were compared and analyzed. Results illustrated that relative humidity has an important effect on coal permeability performance, which will increase the dynamic permeability in coal reservoirs. Accordingly, the effect of coal matrix shrinkage caused by water desorption will increase the dynamic permeability in coal reservoirs. The gas slippage has a little effect on dynamic permeability in coal reservoirs.