鄂尔多斯盆地奥陶系马家沟组自源型天然气聚集与潜力分析

摘要

基于鄂尔多斯盆地天然气勘探新进展,利用地球化学与气源对比等理论与方法,分析该盆地奥陶系马家沟组海相碳酸盐岩烃源岩发育特征,探讨马家沟组自源型天然气聚集规律与潜力.研究认为加里东期古隆起东侧、环盐洼区马家沟组发育规模有效烃源岩,源自马家沟组泥质白云岩与白云质泥岩的天然气是奥陶系气藏的主要贡献者.奥陶系马家沟组不仅发育碳酸盐岩风化壳岩溶储集层,也发育内幕白云岩颗粒滩储集层,且二者分布广泛,均能成为有利储集体.马家沟组天然气以自源型油型气为主,表现为自生自储、近源聚集的特征,只在局部地区存在上生下储的天然气聚集区.同时,提出环盐洼周边地区奥陶系马家沟组具有大规模天然气生成与聚集的有利条件,具备大面积自生自储天然气聚集的优势,靖边气田以西、以北与以南的古隆起前缘洼陷区是未来奥陶系勘探的有利地区.%The characteristics of the marine carbonate source rocks and the accumulation and potential of self-sourced natural gas in the Ordovician Majiagou Formation of the Ordos Basin are investigated based on recent exploration progress by using geochemical and gas-source correlation methods.Massive source rocks are developed around the salt depression,east of the paleo-uplift in the Ordovician Majiagou Formation during the Caledonian;and the natural gases produced by argillaceous dolomite and dolomitic mudstone are the major sources of the Ordovician gas field.Besides widespread carbonate weathering crust karst,internal grainstone dolomite is also well-developed in the Majiagou Formation,and both can act as favorable reservoirs.The natural gas of the Majiagou Formation is mainly self-sourced oil-type gas generated by in-situ source rock and accumulated near the source area.There is only limited local accumulation of natural gas produced in the upper strata and stored below.The Majiagou Formation around the salt depression has favorable conditions for large scale natural gas generation and accumulation,has the advantage of collecting large area natural gas of self-generation and self-preservation and the frontier depression areas of the paleo-uplift to the west,north and south of Jingbian gas field are the potential Ordovician exploration targets in the future.