不同煤级区煤层气可动性和初始排水速度控制策略

对中国20个区块/煤矿煤层气地质参数进行了系统整理，开展了煤层气吸附时间和渗透率随煤级变化规律分析，并结合不同煤级区煤层气井的产气曲线，揭示了峰值产量出现前后不同煤级区产气动态差异的原因，以期为不同煤级区初始排水速度控制提供依据。研究结果表明：①吸附时间随煤级升高呈"U"型变化规律，中、低煤级区煤岩吸附时间一般低于15 d，高煤级区吸附时间变化大，吸附时间在0.1~85.54 d变化；②区块/煤矿间煤储层渗透率随煤级升高没有明显的规律性变化，同一区块内部，渗透率变化级差达2~3个数量级；③峰值产量出现时间与初始排水速度和煤岩吸附时间有较好的对应关系，而与渗透率的关系不明显；④在不同煤级区，针对不同井层煤储层吸附时间与渗透率的配置关系，应采用针对性初始排水速度控制策略：中、低煤级区煤岩吸附时间短，对低渗透井层应严格控制初始排水速度；高煤级区吸附时间变化区间大，对吸附时间长、渗透率高的井层，可适当加快初始排水速度。

Coalbed methane mobility and primary drainage rate control strategy in different coal-rank blocks

The coalbed methane geological parameters of 20 blocks/mines in China are systematically collected and sorted to analyze the change laws of sorption time and permeability varying with coal-rank. In combination with the gas production curves of CBM wells in different rank blocks, this study reveals the reasons for gas production dynamic diversity in different rank blocks prior and posterior to peak production, in order to provide the basis for controlling primary drainage rate in different rank blocks. The studies show that (1) sorption time has a U-shaped variation with the increasing coal-rank. In the low and medium rank blocks/mines, the sorption time is generally less than 15 d; in high rank blocks/mines, the sorption time greatly varies from 0.1 to 85.54 d. (2) Coal reservoir permeability has not varied systemically with the increasing coal-rank between the blocks/mines, but shows 2-3 orders of difference within a block/mine. (3)Peak production time is correspondingly related to primary drainage rate and sorption time, but not evidently related to permeability. (4) In different rank blocks, the primary drainage rate of a well should be controlled according to the allocation relation between sorption time and permeability of coal seams in the well:in low and medium rank blocks, the sorption time is generally short, for the well/seam with low permeability, the primary drainage rate has to be strictly controlled. In high rank blocks, the sorption time varies from short to long, for the well/seam with long sorption time and high permeability, the primary drainage rate can be speeded up appropriately.