高石梯—龙王庙大气田发现与四川盆地震旦—寒武系油气地质特征及成藏

    GEOLOGIC CHARACTERISTICS OF THE LESHAN-LONGNVSI PALEO-HIGH, SICHUAN BASIN AND THEIR BEARING ON HYDROCARBON ACCUMULATION

      摘要
    • 摘要: 简单回顾了高石梯—龙王庙大气田发现历程。高石梯—龙王庙大气田是四川盆地中西部震旦系—寒武系重要的含气领域,近年来龙王庙组的天然气勘探获得重大新突破,基于前人的研究成果,梳理川中震旦系—寒武系勘探与研究进展认为:①高石梯—龙王庙大气田自形成以来,震旦纪晚期为其所处的乐山—龙女寺古隆起整体掀斜与雏形发育,寒武纪—奥陶纪为同沉积隆升期;②大面积发育震旦系灯影组碳酸盐岩缝洞型、寒武系龙王庙组白云岩孔隙型 2 套主要含气储集层,准同生白云石化和表生岩溶叠加改造形成相对高孔渗储集体,灯影组孔隙度为3%~4%、渗透率为(0.0054~9.03)×10-3 μm2,龙王庙组孔隙度为4%~5%、渗透率为(0.0005~78.5)×10-3μm2;③四川盆地震旦系—寒武系发育2类多套烃源岩,均为腐泥型,以生油为主,发育3套优质储层,储层厚度大、分布面积广;④震旦系—寒武系天然气为典型的干气,均为有机成因,其中灯影组天然气为混源气,震旦系—寒武系天然气以原油裂解气为主;⑤生储接触广泛,震旦系—下寒武统龙王庙组油气大面积富集的关键因素是古隆起演化与烃源岩演化匹配,大型鼻状隆起背景下发育的构造、岩性及复合型多种类型圈闭为油气聚集提供了良好的空间。

       

      Abstract: The Gaoshiti-Longwangmiao Gas Field has been an important gas exploration target of Sinian-Cambrian in the western and central Sichuan Basin where gas discoveries have been successively obtained in recent years, including several major ones, such as the Lower Cambrian Longwangmiao gas field. In order to summarize the exploration and research progress in the Sinian-Cambrian in the Sichuan Basin, we made a new round of thorough review of previous studies, and concluded that:(1)The region had been under regional tilting during Late Sinian and the Leshan-Longnvsi Paleo-high was almost in shape, and the region had suffered from syndepositional uplifting during Cambrian and Ordovician.(2)There are two types of gas-bearing reservoirs in the gas field, i.e. fracture-cave type carbonate in the Sinian Dengying Formation and pore type dolomite in the Cambrian Longwangmiao Formation. The penecontemporaneous overlap of dolomitization and karst erosion made available of high porosity and permeability reservoirs, 3%-4% of porosity and (0.0054-9.03)×10-3μm2 of permeability for the Sinian Dengying Formation, and 4%-5% of porosity and (0.0005-78.5)×10-3μm2 of permeability for the Cambrian Longwangmiao Formation.(3)There are multiple layers of source rocks, which could be grouped into two types, in the Sinian-Cambrian of the Sichuan Basin, they are all of sapropel type, favorable for oil generation. There are three sets of high quality reservoirs in the basin with great thickness and extensive distribution.(4)The natural gas in the Sinian and Cambrian is typical dry gas of organic origin in general, except that in the Dengying Formation which was from mixed sources. The natural gas is dominated by crude oil cracking gas in the Cambrian-Ordovician of the Sichuan Basin.(5)The reservoir extensively contact with the source rock. The key factor to cause the great amount of gas accumulation is the contemporaneous development of the Paleo-high with the source rock evolution. Structural, lithological and compound traps developed on a large nose-like uplift provide favorable space for hydrocarbon accumulation.

       

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