The influence of water saturation on the stress sensitivity of medium rank coal reservoirs
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摘要: 为了查明含水饱和度对中阶煤储层应力敏感性的影响，对煤层气井储层改造及排采工作提供指导，利用自主设计的实验装置开展了黔西松河矿龙潭组1+3号、15号煤干燥、含水及饱水条件下液测、气测渗透率应力敏感性实验，分析了煤样渗透率、渗透率损害率、渗透率不可逆损害率、应力敏感性系数变化特征。研究结果表明：随着含水饱和度升高，中阶煤液测渗透率应力敏感性增强，加卸载造成的渗透率不可逆损害率增大。含水饱和度升高导致初始气测渗透率降低，干燥煤样孔裂隙闭合程度高，饱水煤样因束缚水饱和度高，具有较强的气测渗透率应力敏感性。干燥煤样、含水煤样适宜采用幂函数表征无因次气测渗透率与有效应力的关系，饱水煤样则更适合采用负指数函数表征两者关系。中阶煤储层压裂及排采过程中应重视储层保护，当煤储层含水性较弱时，应优先考虑采用CO2或N2泡沫压裂方式进行储层改造。Abstract: In order to ascertain the effect of water saturation on the stress sensitivity of middle-rank coal reservoirs, a self-designed experimental device was used to develop the dryness, water-bearing and water-saturation conditions of seams No.1+3 and No.15. The liquid and gas permeability susceptibility tests were performed to analyze the characteristics of coal sample permeability, permeability damage rate, irreversible damage rate, and stress sensitivity coefficient, and the reservoir gas recovery and drainage of coalbed methane wells were investigated, which possesses a guiding significance for the reservoir reconstruction and drainage work of coalbed gas well. Results show that with the increase of water saturation, the permeability sensitivity of medium-rank coal liquid permeability increases, and the irreparable damage rate caused by loading and unloading increases. The increase of water saturation leads to the decrease of the initial gas permeability, the high degree of fracture closure of the dry coal samples, and the high saturation of the saturated coal-like irreducible water, then it has strong gas-permeability stress sensitivity. The dry coal and water samples are suitable to characterize the relationship between permeability and effective stress of non-dimensional gas by power function. The saturated coal sample is more suitable to characterize the relationship by negative exponent function. During the fracturing and drainage of medium-rank coal reservoirs, attention should be paid to reservoir protection. When the coal reservoirs contain relatively weak water, priority should be given to adopt CO2 or N2 foam fracturing methods for reservoir reconstruction.
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Keywords:
- water saturation /
- medium rank coal /
- stress sensitivity /
- permeability
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