水溶气地球化学特征、演化及其机理研究

The water-soluble gas is a kind of unconventional gas that dissolved in water. The water-soluble gas not only has a huge amount of resources and is important unconventional gas exploration area in the future; it also plays an important role in the formation of today's conventional gas reservoir. The uplift caused by the movement of Himalayan to promote the formation water decompression, the release of natural gas to the gas reservoir to provide additional sources of gas, can also cause gas geochemical characteristics of changes in the gas reservoir. During the gas reservoir exploitation, the release of soluble gas can provide supplementary gas source for the gas reservoir. As the level of awareness of water-soluble gas is not enough, this has impacted the study of the gas origin and accumulation process, gas resource evaluation and exploration thoughts. The studies of geochemical characteristics of water soluble gas, favorable geological conditions for water soluble gas, accumulation mechanism, and gas fractionation mechanism are in the blank. The Sinian, Changxing - Feixianguan and Xujiahe formations, the water-soluble gas resources are very rich, will be carried out the studies on water soluble gas, comparing with the corresponding conventional natural gases. The studies mainly focus on geochemical characteristics and evolution of the water-soluble gas, gas fractionation and its mechanism in water. The studies will have much significance on origin, gas accumulation, and resources evaluation of conventional and unconventional natural gas and to exploration development.

水溶气是溶解在水中的天然气。作为非常规气中一员，水溶气不仅资源量巨大、是未来重要的非常规天然气新勘探领域，其对现今常规气藏的形成也起重要作用。喜山运动造成的地层抬升促使地层水减压脱溶，释放出的天然气不仅可以给气藏提供额外的气源，也能造成气藏中天然气地球化学特征变化。在气层开采降压后，水溶气的释放也可为气藏进行气源补充。由于对水溶气认识程度不够，影响了天然气的成因和成藏过程研究、资源评价和勘探思路。针对水溶气地球化学特征、水溶气成藏有利地质条件、成藏机理、地层水对天然气分馏机理等研究方面的空白，本项目选择四川盆地水溶气资源十分丰富的震旦系、长兴－飞仙关组和须家河组水溶气为研究对象，与相应常规天然气进行对比，来开展水溶气地球化学、水溶气的演化、水对天然气的分馏作用及分馏机理、该研究对天然气成因、天然气成藏、常规与非常规天然气资源评价以勘探部署有重要意义。

本项目针对水溶气地球化学和水溶气形成机理及脱气成藏有利地质条件方面研究比较薄弱的现状，选取四川盆地代表不同烃源岩类型的主力气层（震旦－寒武系、长兴－飞仙关组和须家河组）水溶气和气层气作为研究对象，采取自然脱气和真空水浴脱气以及模拟实验方法，把水溶气地球化学和气层气对比，开展了水溶气地球化学特征、水溶气鉴别、水溶气成藏过程和演化机理等方面的研究；同时对气田水中的有机大分子也开展了初步研究。取得主要成果有：.1．无论是煤型气还是油型气，与游离气相比，发现从水中脱出的甲烷碳、氢同位素都明显偏重，说明水对甲烷碳、氢同位素有明显的分馏作用。该成果为水溶气地球化学研究奠定了较好的基础，也为某些地球化学特征异常的天然气成因鉴别、天然气成藏研究，以及资源评价都有重要意义。.2．水溶气在持续脱溶的过程中，先、后脱出的甲烷碳、氢同位素逐渐变重。这为水溶气脱气过程中气田水的运移路径研究提供重要依据。.3．提出了水溶气演化过程和变化机理：随温度、压力的增加，高（过）成熟烃源岩生成的天然气不断溶解于水，以及游离气与水溶气交换作用，是导致水中溶解的甲烷碳同位素变重的主要原因。.4．分别建立了煤成气和油型气两种类型的天然气水溶气鉴别图版，为水溶气的鉴别提供了依据。.5．发现四川盆地川中须家河组、龙岗气田长兴－飞仙关组、乐山－龙女寺古隆起灯影组和龙王庙组具备较好的水溶气形成以及后期构造抬升水溶气脱气成藏有利地质条件，都存在水溶气脱气成藏的地球化学证据。.6．须家河组气田水苯酚含量较高，反映煤系来源；并且不同层位气田水有机质含量和类型有差异。