木里煤田聚乎更矿区侏罗系天然气水合物成藏要素分析

摘要

To study gas hydrate reservoiring factors and reservoiring assemblages in the Juhugeng mining area,Muri coalfield,have analyzed the Jurassic source rock,reservoir strata and temperature-pressure phase equilibrium conditions,further confirmed study area reservoiring assemblage mode.The result has shown:The Jurassic mudstone,shale in the mining area have higher organic matter abundance,various tested results have reached the argillaceous source rock good organic matter abundance generating rock-medium source rock criterion.Kerogen carbon isotopic δ13C value is between-50.3‰ ～ ～29.6‰,average-41.9‰,organic matter type belongs to sapropel-type kerogen;meanwhile,organic matter Ro is between 0.63％ ～ 1.32％,average 84.05％;the thermal maturity reached the hydrocarbon generation stage;Study area reservoir strata can be partitioned into clastic rock reservoir and fracture reservoir.In gas hydrate discovery sector,fracture developed siltstone,mudstone and oil shale have reservoir spaces,account for 84.05％ of gas hydrate reservoir strata.Gas hydrate reservoir spaces in the area are mainly fractures developed in mudstone and oil shale;Gas hydrate composition in the area is the main factor impacting gas hydrate temperature-pressure phase equilibrium,it further controlled gas hydrate hosting depth;within depth about 120m ～600m range basically satisfied temperature-pressure phase equilibrium conditions to form steady gas hydrate;The Yaojie Formation lacustrine mudstone and oil shale constituted main source rock in the area;and have developed course,medium and fine grained sandstone as well as fissure developed mudstone,oil shale,thus the major reservoir spaces in the area;the frozen soil layer provided the temperature-pressure phase equilibrium condition for steady existence of gas hydrate in Yaojie Formation.In this way has formed the distinctive Yaojie Formation self-generation and self-preservation gas hydrate reservoiring mode in the area.%为了对木里煤田聚乎更矿区的天然气水合物成藏要素和组合进行研究,通过对区内侏罗系的烃源岩、储集层、温-压相平衡条件进行分析,进一步确定研究区的成藏组合模式.结果表明:木里煤田聚乎更矿区侏罗系的泥岩、页岩有机质丰度较高,各项测试均达到了泥质烃源岩有机质丰度好生油岩-中等烃源岩的标准.干酪根碳同位素δ13C值在-50.3‰～-29.6‰,平均值为-41.9‰,有机质类型属于腐泥型干酪根;同时,有机质Ro在0.63％ ～ 1.32％,平均值0.85％,热成熟度达到了生烃阶段;研究区储集层分为碎屑岩储层和裂隙储层,在发现天然气水合物层段粉砂岩、泥岩、油页岩发育的裂隙具有储集空间,占天然气水合物储集层的84.05％,区内天然气水合物的储集空间主要为泥岩、油页岩发育的裂隙;研究区内天然气水合组分是影响天然气水合物温-压相平衡的主要因素,其进一步控制着天然气水合物的赋存深度,约在地下深度120～ 600m基本满足了形成稳定水合物的温-压相平衡条件;木里煤田窑街组湖相泥岩、油页岩构成了研究区主要的烃源岩;窑街组发育的粗砂岩、中砂岩、细砂岩以及裂隙发育的泥岩、油页岩成为研究区的重要储集空间,冻土层的发育为窑街组形成天然气水合物稳定存在的温—压相平衡条件,研究区区形成了自生(窑街组)自储(窑街组)的成藏模式.