柴达木盆地天然气勘探领域

Natural Gas Exploration in Qaidam Basin

根据气源岩特征及分布,结合其他成藏要素、成藏模式和成藏规律,可将柴达木盆地划分为柴北缘侏罗系煤型气、柴西古近系—新近系油型气和三湖第四系生物气3个勘探领域。煤型气勘探领域烃源岩具有分布广、丰度高、生烃强、深埋晚、资源量大的特征,古构造、输导体系和源圈配置是煤型气成藏主控因素,存在盆缘区下组合(基岩—侏罗系—古近系)和盆内晚期构造上组合(新近系)两套储盖组合及源外和源上两种成藏模式;近期主要的勘探领域为盆缘阿尔金山前东段、祁连山前西段下组合(基岩—侏罗系—古近系路乐河组)和盆内的冷湖构造带、鄂博梁构造带上组合(古近系上干柴沟组、新近系下油砂山组)。油型气勘探领域具有3个凹陷、2套烃源岩、3种类型天然气资源特征和环凹分布、近源聚集、接力输导、甜点聚集的油型气富集规律;其晚期成藏表现明显,具"接力式"的运聚模式;烃源岩埋深大、成熟度高、生气强度大、气油比高的区带是油型气勘探的有利区带,包括狮子沟—油砂山—英东和油泉子—开特米里克—油墩子等构造带。生物气勘探领域具有单一气源岩、低丰度、快速沉积的天然气资源特征;具有持续生烃、垂向和侧向运移共存、动态成藏的生物气成藏模式;三湖凹陷北斜坡的鼻隆和背斜外围是岩性气藏有利的勘探领域。

Qaidam basin can be divided into three exploration provinces - Jurassic coal-type gas on the northern periphery of Qaidam Basin, Paleogene - Neogene oil-type gas in West Qaidam and Quaternary biogenic gas in Sanhu area - according to the characteristics and distribution of source rocks as well as other elements, such as the accumulation pattern and law. The source rock of coal-type gas is characterized as wide distribution, high organic abundance, strong sourcing capability, burial in the late periods, and a large amount of reserves. The key controlling factors of coal type gas accumulations in the basin margin area are ancient structures, transport systems and source trap relations. There are two types of reservoir-cap assemblages including lower assemblages （base rock-Jurassic-Paleogene） on the periphery of the basin and upper assemblages （Neogene） of the late structures within the basin. There are also two accumulation models - accumulations outside the source and accumulations above the source. The recent exploration efforts have been focused on the lower assemblages （base rock-Jurassic-E1＋2） in eastern segment in front of Alkin Mountains and the western segment in front of Qilian Mountains as well as the upper assemblages （N1, N21） in Lenghu and Eboliang structural belts inside the basin. Oil-type gas exploration area is characterized as three depressions, two sets of source rocks and three types of reserves, with a number of laws for gas abundance, such as distribution surrounding the depressions, nearsource aeeumulation, relay transport and sweet-spot accumulations. It is obvious that aceumulatiens took place in the late periods, with a ＂relay style＂ for migration and accumulations. Hydrocarbon source rock is deep in burial, high in maturity and strong in sourcing capability. The zones with a high gas-oil ratio are favorable areas for exploration of oil-type gas, such as the Shizigou-Youshashan-Yingdong structural belt and Youquanzi-Kaitemilike-Youdunzi structural belt. Biogenic gas exploration is characterized as a single kind of source rock, low abundance, and rapid deposition, in the pattern of sustainable sourcing, vertical and lateral migration and dynamic accumulations. The nose uplifts on the northern slope of Sanhu Depression and the peripheral zone of anticline are favorable exploration areas for lithologic gas reservoirs.