沁水盆地C-P煤系非常规天然气连续成藏机理研究

Coal-bearing strata are of natural advantages for unconventional gas accumulation such as coalbed methane, tight sands gas and shale gas. Up to now, most of the shtuies only focus on one kind of the gases, the research work which consider the continous accumulation of a variety of unconventional natural gas in the whole coal mearsures, needs to be started. Combining of the Special tests, physical modeling and numerical simulation method, the core issue of the research, i.e. the unconventional natural gas continuous accumulation in the coal measures is discussed basing on the basic view that the Carboniferous-Permian coal-bearing strata in the Qinshui basin is a whole gas system. Generally, this study intends to analyze the coal hydrocarbon generation process, coal reservoir properties evolution, coal-bearing sandstone diagenesis process and basin evolution history. And then seeks to identify the hydrocarbon generation characteristics and hydrocarbon potential of coals with different coal rank and its conrol on the the coal reservoir characteristics; clarify diagenesis process of sandstone in carboniferous - permian coal measures; determine the relation of the coal-bearing sandstone densification and the coal hydrocarbon generation; reveal dynamic transfer mechanisms of the adsorbed gas and the free gas in the coal measures; interpret continuous accumulation mechanism of the unconventional natural gas in coal-bearing strata. This research will be helpful to make full use of the coal-bearing natural gas resources, enhance coalbed methane production of per well, expand the reserve block, rich coalbed methane as well as unconventional natural gas geological theory.

煤系具备煤层气、致密砂岩气、页岩气多种非常规天然气连续富集成藏的天然优势，但目前单项研究较多，以煤系地层为含气系统、考虑多种非常规天然气连续成藏的研究工作亟待展开。项目以沁水盆地为依托，视石炭-二叠煤系地层为一整体含气系统，采用专项测试、物理模拟和数值模拟相结合的方法，就煤系非常规天然气连续成藏这一核心问题，拟分析煤岩生烃过程及其储层物性控制作用、煤系砂岩成岩作用过程、盆地演化过程，力求查明低、中、高煤阶煤的生烃特征和生烃潜力，厘定生烃作用对煤层储集性的控制作用；阐明沁水盆地石炭-二叠纪煤系砂岩的成岩作用过程，厘定煤系砂岩致密化和煤岩生烃的配置关系；阐释煤系地层非常规天然气连续成藏机理，揭示煤系吸附气和游离气动态转移机制。项目成果有助于充分利用煤系天然气资源，提高煤层气单井产量、拓展后备区块，丰富煤层气乃至非常规天然气地质理论。

煤系地层具备煤层气、致密砂岩气、页岩气多种非常规天然气连续富集成藏的天然优势，开发单种非常规天然气资源，单位面积控制资源量有限，采出效率不高，将煤系地层视为统一的含气系统，研究煤系地层的连续成藏机理，对煤系非常规天然的统筹开发有重要意义。项目以沁水盆地和冀中坳陷文安地区C-P煤系地层为依托，以（1）煤岩二次生烃及其储层物性控制作用，（2）煤系砂岩致密过程与生排烃匹配关系研究和（3）煤系非常规天然连续成藏及动态转移机理研究为核心内容，主要取得了以下研究成果：（1）针对C-P本溪组、太原组、山西组地层识别划分了3个三级层序和6个四级层序，不同体系域的成煤特点和岩性组合特征不同；（2）煤岩生烃能力强，吨煤生气超过200m3/t(Ro>2%)，随变质程度增加，由于煤成油充填小微孔，煤岩孔隙度先在煤成油阶段降低减小，而后随着煤成油裂解，以及煤岩大量生气，煤岩孔隙度又开始增大；煤岩吸附能力随变质程度增加成增加趋势，沁水盆地煤岩兰氏体积在25-45 m3/t之间；（3）沁水盆地煤系砂岩致密期主要发生在三叠纪末期。（4）华北地区C-P煤岩主要有两个生烃期，一个在三叠纪末期，另一个为燕山期岩浆热活动期（主生烃期）。（5）成岩演化和成藏配置表明华北地区致密砂岩主要为先致密后充气, 沁水盆地随构造抬升，煤系地层压力降低，煤层气解吸，致密气接受煤层气补给。