煤系气合采层间窜流与层内动态滑脱流耦合作用机理研究

Fine mining is an important mean and an effective way to achieve efficient development of coal measure gas. The dynamic evolution law of migration of coal measures gas is the theoretical basis for fine mining. This project takes coal measures composite reservoirs in Shanxi Province as background and focuses on the dynamic evolution law of migration of coal measures gas in composite reservoirs to achieve fine mining of coal measures in composite reservoirs and maximize production capacity. The mechanisms of interlayer crossflow and dynamic slipstream were analyzed by combining laboratory test with theoretical analysis and numerical simulation. The influences on the coefficient of crossflow and slipstream by matrix-fracture and the change of effective stress was also analyzed. The model of dynamic interlayer crossflow and interlayer crossflow considering dynamic slipping effect was established, and their coupling effect was analyzed. To reveal the dynamic variation process of the migration of coal measures gas in the composite reservoir and the parameters change during combined mining, the difference of depressurization cone whether dynamic variation was considered or not were analyzed separately, then the production capacity forecast model was established when the gas was combined mining. The research results will reveal the dynamic variation process of gas migration in composite reservoirs, also providing the key theoretical and technological support for the design and productivity prediction of coal measures gas combined mining in coal measure composite reservoirs.

精细化开采是实现煤系气高效开发的重要手段和有效途径，煤系气运移的动态演化规律是精细化开采的理论基础。为实现复合储层煤系气精细化开采，最大限度的提高产能，本项目以山西地区煤系复合储层为研究对象，对煤系气在复合储层中运移的动态演化规律进行重点研究。采用实验室试验、理论分析与数值模拟相结合的手段，分析煤系气在复合储层中运移时的层间窜流机理及滑脱机理；研究基质收缩效应和有效应力变化对窜流系数、滑脱系数的影响；建立合采时层间窜流动态演化模型、考虑动态滑脱效应的层内流动模型并分析二者的耦合作用关系，阐明煤系气在复合储层中运移时的动态演化规律；比较考虑动态变化与不考虑时压降漏斗扩展的差异，阐明储层参数变化对煤系气合采的影响；建立煤系气合采时的产能预测模型。项目研究成果将揭示煤系气在复合储层中运移时的动态演化规律，为实现复合储层煤系气精细化开采、高效开发提供理论依据。

我国石炭-二叠纪地层广泛发育着煤层气、页岩气、砂岩气复合成藏的煤系气藏，对于该类气藏实施多层合采可有效提高单井产气量、储量动用程度、开采年限和产气率等。但目前煤系气的开采主要以煤层气为主，而对复合储层煤系气合采的研究与应用较少。煤系气在复合储层中的运移规律与在单一储层中不同，其不仅存在层内流动，还存在层间流动，并且两者耦合作用，其运移过程比在单一储层中的运移复杂得多。清楚、准确地认识煤系气在复合储层中的运移机理及规律是煤系气合采及产能预测的基础，也是当前煤系气合采亟需解决的关键科学问题。鉴此，本项目采用理论分析、实验室试验和数值模拟的方法系统地研究了煤系气在复合储层中的运移规律及机理，为实现煤系气合采产能的准确预测提供了一定的理论基础和指导。本项目的主要工作与取得的主要结论为：（1）以体积不变假设和火柴棍模型为基础，建立了煤系气合采时滑脱系数的动态演化模型，揭示了煤系气合采时滑脱系数随孔隙压力降低呈先减小后增大的变化规律。（2）基于滑脱系数动态演化模型，建立了考虑动态滑脱效应的气体渗透率预测模型。该模型克服了以往模型参数获取困难、经验参数多等困难，具有更高的理论和实用价值。（3）以垂向平衡假设、等效窜流层假设为基础，建立了考虑层间窜流和层内动态滑脱流耦合作用的复合储层煤系气运移模型。该模型考虑了层间窜流、层内动态滑脱流及其耦合作用的影响，更符合复合储层煤系气合采时的煤系气的运移过程。（4）以建立的考虑层间窜流与层内动态滑脱流耦合作用模型为基础，对东曲矿煤系复合储层合采时的产能进行了预测，揭示了层内动态滑脱流和层间窜流耦合作用对煤系气合采产能预测的影响，并指出在产能预测时若忽略其耦合作用易出现产能预测值偏高的现象。