中国煤系气共生成藏作用研究进展

煤系气共生共探与共采受到我国天然气行业的高度关注,勘探与开发试验已经取得了一定的成效。在分析煤系气地质条件特殊性的基础上,从煤系砂岩储层致密化机理、煤系气共生组合及成藏要素配置、煤系含气系统叠置性等方面,评述了我国煤系气共生成藏作用的研究进展。研究结果表明:(1)煤系气地质条件的特殊性表现在3个方面——煤系气赋存态和储层岩石类型具有多样性,其成藏效应与常规砂岩气有所不同;煤系沉积序列旋回性极强,气、水分布关系复杂多变;煤系砂岩储集体在广覆式泥质岩中镶嵌展布。(2)煤系富有机质特性以及烃源岩生气过程产生的有机酸,是煤系砂岩储层致密化的重要诱因,煤系砂岩气可能具有部分自生自储及吸附气的成藏特点,并可在一定程度上改善砂岩储层的物性。(3)煤系沉积特点决定了煤系气成藏效应主要取决于生烃强度、运移方式与输导体系、地层流体能量、区域有效盖层等4个方面,特殊的输导体系使得烃源岩生成的天然气在复杂的源储系统中得以重新分配,这是煤系气共生成藏的重要基础。(4)含气系统叠置性是煤系气地质研究的前缘方向之一,近年来发展了测井响应识别技术和含气系统叠置性判识方法,发现煤系存在3种典型流体压力曲线类型,并初步应用于煤系气共采有利层段的优选。

Research progress of symbiotic accumulation of coal measure gas in China

Coal measure gas (CMG), referring to natural gas stored in coal measures, as well as its existence, exploration and production, has been highly concerned recently in natural gas sector in China, and pilot tests of which have been succeeded with some achievements. To provide new geological references, this paper discussed the research progress in CMG co-existence and pooling factors in the respects of the tightening mechanism of coal measure sandstone reservoirs, CMG co-existence and gas pooling assemblages, the superimposed CMG system, and so on. The following findings were obtained. (1) The particularities of CMG geological conditions are shown in three aspects: First, the occurrence and reservoir lithology of CMG are diverse, and the accumulation of sandstone gas in coal measures may be different from that of conventional sandstone gas. Second, the sedimentary environment of coal measures causes the frequent and thin interbedding with various lithologic reservoirs, strong cyclicity and complex gas–water relationship, and the Surat-type CMG is worthy of attention. And third, the sandstone reservoirs in coal measures are embedded in the wide overlying mudstones, the special source–reservoir match and composite gas reservoirs need to develop adaptive co-exploration and co-production technology. (2) The coal measures are rich in organic matters, and a large number of the organic acids are formed during gas generation from the source rocks, which are important factors for the densification of the sandstone reservoirs in coal measures. And the sandstone reservoirs in coal measures may be characteristic of self generating and self storing gas and adsorption to a certain extent, and their physical properties can be improved by organic detritus in the reservoirs. (3) The sedimentology of coal measures defines four generalities for favorable CMG accumulation, but effect of the gas-generating intensity, gas migration system, formation fluid energy and effective regional caprock thickness to the accumulation are variable. The natural gas generated in source rocks is re-allocated with a special migration system in a complex source–reservoir system, which is an important basis of CMG accumulation. (4) The superimposition of the gas-bearing system is one of the leading problems in CMG research. In recent years, the logging response identification technology of key strata and the superposition identification method of the gas-bearing system have been further developed. It is found that there are three typical types of fluid pressure curves in coal measures. At the same time, the CMG co-accumulation in the whole sense requires a certain threshold depth. Based on the progress above, the theory of CMG accumulation has been improved and deepened, which is helpful in providing more pertinent suggestions for the development of the joint CMG exploration and mining technology.