准噶尔盆地克拉美丽气田及周缘天然气成因来源再认识与勘探启示

Origin of natural gas in the Kelameili Gas Field in the Junggar Basin and its periphery:Re-understanding and its implications for natural gas exploration

克拉美丽气田石炭系气藏已探明天然气地质储量832.4×10^(8) m^(3),是准噶尔盆地已发现的最大天然气田。为了进一步探索、评价、深化对克拉美丽气田及其周缘天然气气源潜力认识,推动发现新气田,对5套地层、38口井、65个天然气样品进行分析,并基于天然气组分和天然气稳定碳同位素组成,系统研究了其成因、来源和遭受的次生改造作用,提出了新的天然气勘探领域。研究结果表明:(1)克拉美丽气田及其周缘存在4种不同成因来源的天然气,第Ⅰ类和第Ⅱ类天然气为煤成气,第Ⅲ类天然气为浅埋藏期伴生原油发生生物降解形成的次生生物成因气(混合热成因气),第Ⅳ类天然气为油型气;(2)部分天然气样品Δδ^(13)C(C_(3)—C_(2))和i-C_(4)/n-C_(4)值异常增加,其重烃气组分遭受了细菌的选择性降解;(3)石炭系滴水泉组烃源岩较巴塔玛依内山组烃源岩分布更广,连续性更好,规模更大,二叠系平地泉组烃源岩在盆地南部已普遍达到高成熟—过成熟阶段,滴水泉组和平地泉组2套烃源岩形成的含油气系统有望成为盆地深层—超深层天然气规模勘探的新领域;(4)次生生物成因气埋藏浅,甲烷浓度高,开采成本低,建产快,且在准噶尔盆地广泛分布,是浅层天然气高效勘探的重要领域。结论认为,天然气成因来源的再认识深化了准噶尔盆地克拉美丽气田及其周缘天然气资源的认识,揭示了盆地深层—超深层和浅层天然气是天然气勘探战略接替领域,对推动盆地实现以石油勘探为主向“油气并举”的重大转变提供了重要技术参考。

The Kelameili Gas Field is the largest gas field that has been discovered in the Junggar Basin,and its Carboniferous gas reservoirs have the proved natural gas in place of 832.4×10^(8) m^(3).In order to further explore,evaluate and determine the natural gas source potential in the Kelameili Gas Field and its periphery and drive the discovery of new gas fields,this paper analyzes 65 natural gas samples taken from 5 reservoirs and 38 wells.Then,based on the components and stable carbon isotope compositions of natural gas,its origin and secondary reworking are researched systematically,and the potential natural gas exploration fields are pointed out.And the following research results are obtained.First,the origin of natural gas in the Kelameili Gas Field and its periphery is classified into four types,among which,type I and II are coal-derived gas,type III is secondary biogenetic gas derived from the shallow associated oil through biological degradation(mixed thermogenic gas) and type IV is oil-type gas.Second,the Δδ^(13)C(C_(3)-C_(2)) and i-C_(4)/n-C_(4) values of some natural gas samples increase abnormally,indicating that their heavier-hydrocarbon-gas components were selectively degraded by bacteria.Third,compared with the Batamayineishan Formation source rocks,the Dishuiquan Formation source rocks have wider distribution,better continuity and larger scale.The Pingdiquan Formation source rocks have generally reached high to over-mature stage in the southern Junggar Basin.The petroleum system with the Dishuiquan Carbonifeous Formation and Pingdiquan Permian Formation source rocks is a potential new field for large-scale exploration of deep and ultra-deep natural gas in the Junggar Basin.Fourth,secondary biogenetic gas reservoir is an important field for efficient exploration of shallow natural gas due to its shallow burial,high methane concentration,low production cost,fast productivity construction and wide distribution in the Junggar Basin.In conclusion,re-understanding the origin of natural gas makes the natural gas resources in the Kelameili Gas Field and its periphery in the Junggar Basin understood further,and reveals that deep and ultra-deep natural gas and shallow natural gas in the Junggar Basin are strategic replacement fields of natural gas exploration.The research results provide an important technological reference for the great transformation from oil exploration to simultaneous development of oil and gas.