青海木里三露天井田煤系天然气水合物成藏模式与勘查开发建议

Accumulation model and exploration and development suggestions of coal measure gas hydrates in Sanlutian area of Muli Coalfield, Qinghai Province

天然气水合物因其能量密度巨大、使用方便、燃烧值高、清洁无污染等特点,被誉为21世纪最有希望的战略资源,是常规油气资源的潜力巨大的一种替代能源。青海木里地区三露天井田天然气水合物的发育是该区含煤岩系的充足气源和高寒山区适宜的水合物稳定带耦合作用的结果。将赋存在煤系中的天然气水合物定义为煤系天然气水合物,并将其纳入煤系非常规天然气范畴。为查明其与含煤岩系的密切联系和成矿专属性,探讨煤系天然气水合物的赋存条件,提出勘查开发建议。研究表明:三露天井田煤系天然气水合物气源兼具煤型气与油型气特征,富集层位集中在温压稳定带的中侏罗统江仓组上段,储集层类型及所占比例依次为“裂隙型”65.22%、“裂隙+孔隙型”26.08%、“孔隙型”8.70%。根据现今构造格局,三露天井田被划分为8个区块,其中,以逆断层发育为主、低地层倾角及中-低等断裂密度发育程度的M_(1)、S_(1)和S_(2)区块为天然气水合物的有利富集区。建立了三露天井田煤系天然气水合物成藏模式,即叠瓦扇式构造与冻土带封堵型,混源充注、短距运移、构造圈闭是研究区天然气水合物形成的有利因素。最后,以研究区煤系天然气水合物为实例,总结了陆域煤系天然气水合物的基本特点,提出了我国冻土区天然气水合物勘查开发的调查、勘查、开采3个阶段,指出煤系气共探合采是煤系天然气水合物开发的必然途径。

The Natural Gas Hydrate(NGH) is known as the most promising strategic resource in the 21st century because of its huge energy density, convenient use, high combustion value, and cleanness, and it is an alternative energy source with huge potential for conventional oil and gas resources. The occurrence of the NGH in the Sanlutian area of Muli Coalfield in Qinghai Province is the result of the interaction between the abundant gas sources and the hydrate stability zone in cold highland areas. The NGH in coal-bearing strata is defined as the coal measure gas hydrate, belonging to unconventional coal measure gases. To find out its close connection with coal measures and its metallogenic specialization, the accumulation conditions of the NGH are studied, and proposals for the exploration and development of the NGH are put forward in this paper. The results show that the NGH in coal measures in the Sanlutian area of Muli Coalfield is characterized by both coal-type gases and oil-type gases, and the enrichment layers are concentrated in the upper part of Jiangcang Formation of the middle Jurassic in the temperature-pressure stable zone. The reservoirs of the NGH can be divided into “fracture type”, “fracture + pore type” and “pore type”, of which the proportion are 65.22%26.08% and 8.70%, respectively. Based on the present tectonic pattern, the Sanlutian area is divided into eight blocks,and the favorable enrichment areas of NGH are the M_(1), S_(1) and S_(2) blocks with the development of reverse faults, low dip angle of strata, and medium to low fracture density. The accumulation mode of the NGH in coal measures in the Sanlutian area is established, that is, imbricate fan structure and frozen soil zone plugging type. The mixed gas source filling,short-distance migration, and tectonic trap are favorable factors for the NGH accumulation. Finally, with the coal measure NGH in the study area as an example, the basic characteristics of the terrestrial coal measure NGH are summarized,and three stages of the exploration and development of the NGH in the permafrost area in China are proposed. It is considered that co-exploration and mining is an inevitable way to develop the NGH in coal measures.