典型碳酸盐岩大气田规模聚集差异性及其主控因素——以四川盆地安岳气田和鄂尔多斯盆地靖边气田为例

Differences and main controlling factors of large-scale gas accumulations in typical giant carbonate gas fields:A case study on Anyue gas field in the Sichuan Basin and Jingbian gas field in the Ordos Basin

四川盆地安岳气田和鄂尔多斯盆地靖边气田分别是中国迄今为止发现的总体规模最大和单层规模最大的两个海相碳酸盐岩特大型气田。基于对成藏体系理论中的气藏源-位结构、油气成藏过程及关键要素时-空配置等的解剖,认为安岳气田和靖边气田发育多种源-位结构,烃源体-圈闭体高效配置,但安岳气田为继承性古隆起上的古油藏裂解气“原位”聚集成藏,而靖边气田为斜坡背景构造转换枢纽带调整成藏。三大关键因素控制安岳和靖边两类大气田的规模富集:(1)烃源体均经历异常热事件,热流值超过70 mW/m^(2)的热事件持续时间约70 Myr,不同类型烃源体已充分裂解并形成以甲烷为主的气体,气源充足;(2)发育有利岩相叠加岩溶作用的多层叠置规模优质储集体,有良好的储集空间;(3)发育构造、构造-岩性、地层-岩性、岩性等多类型规模圈闭体,具备规模有效聚集场所。古油藏范围内或邻近烃源体的高能滩体与岩性致密带匹配区是下一步寻找规模天然气聚集的有利勘探领域。

Anyue gas field in the Sichuan Basin and Jingbian gas field in the Ordos Basin are two giant marine carbonate gas fields with the largest overall scale and the largest single-layer scale respectively discovered in China so far.Based on the analysis of the source-location structure of gas reservoirs,the process of gas accumulation and the space-time configuration of key play elements during reservoir generation,we consider that Anyue and Jingbian gas fields are characterized by a variety of source-location structure types and source-trap configuration of high efficiency.However,Anyue gas field is of“in-situ”accumulation of pyrolysis gas from paleo-oil reservoirs in inherited paleo-uplift,while Jingbian gas field is of adjusted accumulation in the structural transformation zone of a slope.There are three key factors controlling the large-scale enrichment of Anyue and Jingbian gas fields.First,the hydrocarbon source rocks underwent abnormally thermal events,with the duration of thermal events with a heat flow value over 70 mW/m^(2) being about70 Myr.Different types of kerogen got fully cracked to generate methane-dominated gases in large amount.Second,the multi-layered reservoirs of large scale and high quality are well developed due to the modification of favorable lithofacies by karstification.Third,many types of large-scale traps are well developed including structural,structural-lithologic,stratigraphic-lithologic and lithologic traps,being favorable for large-scale and effective accumulation of gas.The areas with ideal configuration relationship between high-energy beach body and lithologically tight zone within paleo-oil reservoirs or adjacent to hydrocarbon source rocks are favorable for discovering large-scale gas accumulation in the near future.