塔里木盆地顺北碳酸盐岩元素地球化学特征与油气富集机制

Geochemical characteristics and oil&gas enrichment mechanisms of carbonate rocks in Shunbei area of Tarim Basin

石油和天然气是重要的战略资源。深地油气因其储量丰富但地质条件复杂,成为近年来油气行业广泛关注的热点。作为中国石化首个以“深地工程”命名的油气项目,塔里木盆地顺北地区油气田深地油气勘探基础理论研究对中国更好地端牢能源饭碗具有重要意义。选取采自塔里木盆地顺北地区控制油气储量区的工业油气流井——SB47钻井岩心(屑)样品进行元素地球化学分析,结合测井、录井、钻井实际工况以及矿物学与岩石学资料,探讨顺北地区奥陶系碳酸盐岩元素地球化学特征和孔缝洞建造机理与油气富集机制,以期为该地区油气勘探开发工作提供理论支撑。主要成果:(1)SB47井的元素地球化学特征可以很好地指示顺北地区奥陶系碳酸盐岩普遍存在的白云岩化现象。顺北地区奥陶系碳酸盐岩Ca、Mg元素的“镜像”变化趋势反映了白云岩化作用的强弱变化;Fe、Mn、Sr、Ba含量与Ca、Mg含量的协同变化反映了白云岩化作用对元素富集和迁移的控制作用。(2)结合声波时差、电阻率、气测全烃以及成像测井等测录井资料,SB47井的元素地球化学特征可以很好地判断顺北地区奥陶系碳酸盐岩孔缝洞的成因和充填物类型。声波时差大、电阻率低和气测全烃值高表明地层发育孔缝洞或伴有油气水充填,Ca、Mg元素的“镜像”变化表明地层发育白云岩化成因孔缝洞,Si、Fe、Mn、Ti、Al、K的含量增大表明孔缝洞为泥质充填。基于研究成果及顺北地区控制天然气储层和工业油气流井均沿断裂带发育的客观事实,提出顺北地区奥陶系碳酸盐岩孔缝洞建造机理与油气富集机制。结论认为,构造裂缝形成低压区,利于油气富集产出;构造裂缝为地表水自上而下运移、热液流体自下而上运移及深埋藏封存流体侧向运移提供了通道,导致断裂带附近成岩作用明显和孔缝洞的发育,进而成为油气聚集带。

Oil and natural gas are important strategic resources in China.Deep oil and gas due to its abundant reserves but complex geological conditions,have become a hot topic of widespread concern in the oil and gas industry in recent years,and are still thriving to this day.As the first oil and gas project in Sinopec named after the“Deep Earth Project”,the basic theoretical research on deep oil and gas exploration in the Shunbei oil and gas field is of great significance for China to better secure its energy rice bowl.It is selected the industrial oil and gas flow well SB47 drilling core(debris)samples collected from the control oil and gas reserves area in Shunbei area of Tarim Basin for elemental geochemical analysis.Combining well logging,mud logging,actual drilling conditions,and mineralogical and petrological data,the article explores the geochemical characteristics of Ordovician carbonate rocks in Shunbei area,as well as the mechanism of pore and fissure construction and oil and gas enrichment,in order to provide theoretical support for oil and gas exploration and development work in the area.The main results of this article are as follows:(1)The geochemical characteristics of well SB47 can effectively indicate the widespread dolomitization phenomenon of Ordovician carbonate rocks in the Shunbei area.The“mirror change”trend of Ca and Mg elements in the Ordovician carbonate rocks in the Shunbei area reflects the strength of dolomitization;The synergistic changes in Fe,Mn,Sr,Ba content and Ca,Mg content reflect the controlling effect of dolomitization on element enrichment and migration.(2)By combining logging data such as acoustic time difference,resistivity,gas logging of all hydrocarbons,and imaging logging,the geochemical characteristics of well SB47 can effectively determine the genesis and filling material types of Ordovician carbonate pores and fissures in the Shunbei area.A large acoustic time difference,low electrical resistivity,and high total hydrocarbon value in gas logging indicate the development of pores and fissures in the formation or accompanied by oil,gas,and water filling.The“mirror image”changes of Ca and Mg elements indicate the development of dolomite induced pores and fissures in the formation.An increase in the content of Si,Fe,Mn,Ti,Al,and K indicates that the pores and fissures are filled with mud.Based on the research results and the objective fact that oil and natural gas reservoirs are developed along fault zones in the Shunbei area,the mechanism of pore and fissure construction in the Ordovician carbonate rocks and the mechanism of oil and gas enrichment in the Shunbei area are proposed:On the one hand,the formation of low-pressure zones through structural fractures is conducive to the enrichment and production of oil and gas;On the other hand,structural fractures provide channels for the upward migration of surface water,the upward migration of hydrothermal fluids,and the lateral migration of deeply buried sealed fluids,leading to significant diagenesis and the development of pores and fissures near the fault zone,thereby becoming an oil and gas accumulation zone.