考虑逸散过程的煤层气藏采收率计算模型

Computing model of coalbed methane recovery based on escaping process

通过定义煤层气的压降波及效率、解吸效率与游离气滞留率,提出了一种煤层气采收率的分析计算公式.在此基础上研究了开采过程中煤层气的逸散过程,认为煤层气的逸散是由逸散速度比与逸散距离比共同决定,若煤层气逸散距离比大于逸散速度比的最大值,则可以认为煤层气无法发生逸散.同时,模拟计算了不同地质及工程因素对煤层气的采收率、压降波及效率、解吸效率和煤层气逸散比例的影响.研究结果表明:开采过程中煤层气的逸散可以损失10%左右的储量,距井眼70m以外的煤层气均会逸散至顶板.中等含气煤层的逸散量相较于高含气和低含气煤层的逸散量多.废弃压力对逸散的影响并不单调,可以优化废弃压力使逸散量达到最小.合适的井网以及负压采气措施可以有效降低逸散量,提高煤层气的采收率.

By defining the CBM （coalbed methane） pressure drop spread efficiency, desorption efficiency and free gas detained ratio, a recovery calculation formula was put forward. On the basis, the escaping process during the CBM production was analyzed, which considered that the escaping was determined by both the escaping velocity ratio and escaping distance ratio; if the escaping distance ratio is larger than the maximum value of escaping velocity ratio, the gas can be assumed not escaping from the combed. Meanwhile, effects of different engineering and geological factors on CBM recovery, pressure drop spread efficiency, desorption efficiency and escaping ratio were simulated and computed. The results show that the escaping during CBM production can lead to gas loss of approximately 10% of gas in place, and the CBM 70 m away from the well would escape to the roof. The reservoirs with intermediate gas content can suffer a higher escaping loss than that of reservoirs with high and low gas content. The influence of abandoned pressure on escaping is not simple, and the optimization of abandoned pressure can result in the minimum escaping. An appropriate well pattern and negative pressure production method can dramatically decrease the escaping volume to enhance the CBM recovery.