生物气分布特征和成藏条件

DISTRIBUTION CHARACTERISTICS AND RESERVOIR FORMATION CONDITIONS OF THE BIOGENETIC GAS

生物气储量占世界天然气储量的20%以上,产量占天然气产量的10%以上,因此,生物气是一种重要类型的天然气资源。由于生物气气田(藏)具有分布广、埋藏浅、勘探开发成本低、资源量大、便于利用等特点,正日益引起世界各国的重视。生物气区别于热成因气,它的生成和分布有其自身独特的特征:盆地具有有利的生成条件(Ⅱ-Ⅲ型干酪根、寒冷的气候条件、还原环境、中性水介质条件和较快沉积速度等);盆地类型以年轻的坳陷型陆相沉积盆地为主,并且盖层稳定发育,后期构造稳定;气聚集在生气坳陷中心或邻近中心的隆起、早期圈闭及同沉积圈闭中。在前人研究的基础上,主要以西西伯利亚盆地和柴达木盆地东部为典型实例,总结了世界上生物气田(藏)的分布特征和成藏地质条件,期望对我国生物气勘探有指导意义。

Biogenetic gas reserves account for more than twenty percent of the world natural gas reserves and its output accounts for more than ten percent of natural gas output, therefore, biogenetic gas is an important kind of natural gas resources. Because biogenetic gas has characteristics with wide distribution, shallow burry, low exploration cost, abundant in resources and convenient for use, countries in the world have been paying attention to biogenetic gas. Biogenetic gas is discriminated from thermogenetic gas lying in its special characteristics of generation and distribution. The basin had beneficial generation conditions when biogenetic gas generated, such as Ⅱ-Ⅲ kerogen, cold weather, reducing environment, neutral aqueous medium and high speed sedimentation etc, and the basin is a young depression with land facies sedimentary and the basin has stable cap rock and later structure. Biogenetic gas accumulated in the depression center or in the uplift, early entrapment and syndeposit entrapment near the center. On the basis of predecessor studies, distribution characteristics and reservor formation geological conditions of biogenetic gas in the world are summarized by mainly taking the west Siberia basin and the eastern Qaidam basin for typical examples. This study has certain significance in guiding biogenetic gas exploration in our country.