青海木里三露天冻土天然气水合物成藏模式研究

摘要：祁连山地区天然气水合物分布较为复杂，急需对该区天然气水合物成藏控制因素与成藏模式进行深入研究。本次重点对青海木里三露天天然气水合物系 列钻井揭示的地质资料及各种样品分析测试结果进行综合分析，结果显示：该区天然气水合物气源以油型热解成因气为主，少部分在浅部混有部分微生物成因气及煤成气，这些油型热解成因 气源主要由下部或更深部上三叠统或二叠系提供；当气源岩生成烃类气体后运移至浅部直接或间接由断裂连同泥岩、油页岩等封堵形成浅部气体聚集；浅部气体聚集体局部加入微生物成因气 或煤成气，经过不晚于中更新世早期形成的岛状永久冻土作用，在天然气水合物稳定带内与水结合形成天然气水合物，当它们处在天然气水合物稳定带之外便在更浅部以异常高压气层或游离( 吸附)气存在。由于气源类型与供应条件、运移与聚集条件、天然气水合物稳定带范围的不同，它们之间的匹配关系在不同位置具有很大的差异性，从而影响该区天然气水合物在横向平面上和 纵向剖面上分布与产出的不均性。

Study on the Accumulation Pattern for Permafrost-associated Gas Hydrate in Sanlutian of Muli,Qinghai

The distribution of gas hydrate is very complex in Qilian area, therefore it is urgent to study the controlling factors and the formation pattern of gas hydrate in this area. The geological data and analytical results of various samples collected from the series of gas hydrate drilling holes are emphatically studied in Sanlutian. Results show that gas source for gas hydrate in the study area is mainly composed of oil-typed thermo-genic gases and this kind of gas source is partially mixed with some biogenic gas or coal gas in the shallow. And the oil-typed thermo-genic gases are mainly derived from lower or deeper Upper Triassic or Permian. When gas source migrated upward and arrived at the shallow formation, gases were directly or indirectly blocked by fracture and other seals such as mudstone, oil shale, thus causing shallow gas accumulation. Shallow gas was locally added by microbial gas or coal gas. They together with water were formed into gas hydrate in gas hydrate stability zone after these gases were encountered into frozen formation which happened no later than early Middle Pleistocene. Parts of them still exist as abnormally high-pressured gas reservoir or free (adsorbed) gases in shallower strata when they are outside of the gas hydrate stable zone. Because of variation of gas source types and supply conditions, migration and accumulation conditions, and range of gas hydrate stability zone, these factors’matching relation is various at different location, which affects occurrence and distribution of gas hydrate in a horizontal plane and vertical profile in this area.