煤层群煤系多套含气系统特征及其合采效果

煤系含气系统特征影响了煤层气井多产层合采的工程效果。基于铁法盆地阜新组层序地层、含气单元及其分隔层特征，划分了叠置的多套含气系统，分析了发育煤层群煤系多套含气系统的含气性、渗流条件和流体压力特征，探讨了其对上、下含煤段分采及合采工程效果的影响。研究认为，白垩系阜新组上含煤段5个含气单元为一套统一的含气系统，下含煤段7个含气单元可划分为三套含气系统。湖进体系域下，三角洲前缘沉积环境形成的含气单元资源丰度较大，滨浅湖沉积环境形成的（泥质）粉砂岩厚度大且构成稳定的隔水阻气层，是研究区含气系统划分的关键层。随埋深的增加，各含气系统储层孔隙度、平均渗流孔容、裂隙发育情况、储层渗流能力降低趋势明显。上下含煤段分属明显不同的含气系统，其储层压力、解吸压力差异较大，煤层气合采时上下含煤段储层产出气液具不同步性，气水产出层间干扰大。阜新组煤层气合采效果由好到差的相对顺序是上含煤段合采、上下含煤段合采、下含煤段合采。阜新组上含煤段独立开发的效果最好，是由于各个含气单元形成了一套兼容性含气系统，储层具有明显地富气高渗优势。

Characteristics of Multi-gas-bearing Systems within Coal Seam Groups and the Effect of Commingled Production: A case study on Fuxin Formation,Cretaceous, Tiefa Basin

The characteristics of multi-gas-bearing systems affect the outcome of commingling the production of coalbed methane （CBM） from multiple strata. In this case study， multiple superimposed gas-bearing systems in the Fuxin Formation， Tiefa Basin， are categorized by their stratigraphical sequence and the properties of the non-gas-bearing strata lying between the gas-containing units. The gas-bearing characteristics， seepage conditions and fluid pressures of each CBM system were analyzed to consider the effect of separate and commingled production of gas from the upper and lower coal sections. It was found that each of the five gas-containing units in the upper coal-bearing section are all part of a single gas-bearing system， whereas the seven gas-containing units in the lower coal-bearing section comprised three distinct gas-bearing systems. A transgressive lacustrine system tract had resulted in a relatively large abundance of CBM gas-bearing units at the delta front. In the study area， thick， stable water- and gas-barrier layers of lake-shore and shallow-lake subfacies form the strata between the gas-bearing systems. With greater burial depth， the reservoir porosity， average seepage pore volume， fracture development and reservoir seepage capacity of each gas-bearing layer all decrease significantly. The large difference in reservoir pressure and critical desorption pressure between the upper and lower coal-bearing sections occur because they belong to different gas-bearing systems. The supply of both water and gas in the upper and lower sections are not synchronized in commingled production of the upper and lower coal sections， causing very significant interference in gas and water production. Commingled production of CBM， from best to general， is: （i） from the upper coal-bearing section； （ii） from the upper-plus-lower coal-bearing sections； and （iii） production from the lower coal-bearing section only. Production （i） is best because its various gas-containing units form a single compatible gas-bearing system， and its reservoirs also have the obvious advantages of rich gas content and high permeability.