摘要
近期,四川盆地威寒1井上奥陶统宝塔组孔隙型白云岩测试获工业气流,取得了奥陶系天然气勘探的重大突破。然而,目前对这套白云岩的成因认识不清,制约了该套储层后续的勘探开发。为此,基于老井资料复查和1∶20万区域调查图幅露头资料的重新梳理,并对岩屑、岩心和露头样品开展了镜下观察和碳/氧稳定同位素、原位微区微量元素分析测试,在查明白云岩岩石学特征、空间展布规律和地球化学特征的基础上,建立了四川盆地南部及周缘上奥陶统白云岩的成因模式。研究结果表明:①研究区上奥陶统主要发育细中晶白云岩、粉细晶白云岩和灰质白云岩,细中晶白云岩主要发育于盆外的上奥陶统大箐组,粉细晶白云岩和灰质白云岩主要发育于大箐组和盆内威远地区的宝塔组,宝塔组粉细晶白云岩发育晶粒自形程度高、晶间孔发育的层状孔隙型储层。②区内上奥陶统白云岩具有轻稀土亏损、重稀土富集、镧正异常、铈负异常和钇正异常的特点,反映了白云石化流体的海源属性;白云岩氧同位素相对正常海水沉积明显偏重且发育石膏假晶,并分布在向上变浅序列上部和台洼、潮坪等受限环境中,表明白云石化流体可能为蒸发海水,其自上而下的渗入并白云化下伏地层是白云岩形成的主要途径。③研究区可识别出“潮坪卤水源型”和“潟湖卤水源型”2种白云岩成因类型,前者为蒸发潮坪沉积物孔隙间的重卤水下渗形成的白云岩,如盆内威远地区宝塔组白云岩;后者为局限潟湖下部堆积的重卤水下渗形成的白云岩,如盆外越西—彝良一带形成的大箐组白云岩。结论认为,川中古隆起北斜坡的宝塔组可能发育潮坪相白云岩,有望成为下一步风险勘探的重要对象。
The industrial gas flow tested recently in Well Weihan 1 in the porous dolomite of the Upper Ordovician Baota Formation in the Sichuan Basin marks a significant breakthrough in the exploration of Ordovician natural gas.So far,however,the genesis of this set of dolomite has not been understood yet,which hinders its subsequent exploration and development.In this paper,the data of old wells are reviewed,and the outcrop data in the 1∶200000 regional survey map is sorted out again.In addition,microscopic observation and carbon/oxygen stable isotope and in-situ micro area trace element analysis and test are performed on cuttings,cores and outcrops samples.Finally,the petrologic characteristics,spatial distribution patterns,and geochemical characteristics of the dolomite are clarified.Based on this,the genesis model of the Upper Ordovician dolomite in the southern and peripheral Sichuan Basin is established.The following results are obtained.First,the Upper Ordovician in the study area is mainly composed of fine to medium-crystalline dolomite,powder to fine-crystalline dolomite,and limy dolomite.The former is mainly developed in the Upper Ordovician Daqing Formation outside the basin,while the latter two are primarily developed in the Daqing Formation and the Baota Formation in the Weiyuan area inside the basin.The powder to fine-crystalline dolomite of the Baota Formation constitutes a layered porous reservoir with highly automorphous crystalline grains and developed inter-crystalline pores.Second,the Upper Ordovician dolomite in the study area is characterized by light rare earth element depletion,heavy rare earth element enrichment,positive La anomaly,negative Ce anomaly,and positive Y anomaly,which reflects a marine origin of the dolomitized fluids.Additionally,the dolomite's oxygen isotopes are significantly heavier than normal seawater deposits,and gypsum pseudomorph is developed and distributed in the upper parts of upward shallowing sequences and the restricted environments such as tidal flats and sags,which suggests that dolomitized fluids may be evaporated seawater,and their infiltration from top to bottom to dolomitize the underlying strata is the main pathway for the formation of dolomite.Third,two types of dolomite genesis are identified in the study area,i.e.,"tidal flat brine-sourced type"and"lagoon brine-sourced type".The former refers to dolomite formed due to the infiltration of heavy brine water between pores in evaporative tidal flat sediments,such as the Baota Formation dolomite in the Weiyuan area inside the basin.The latter refers to dolomite formed by the infiltration of heavy brine water accumulated in the lower parts of restricted lagoons,such as the Daqing Formation dolomite in the Yuexi-Yiliang area outside the basin.In conclusion,there may be tidal flat dolomite developed in the Baota Formation at the northern slope of Central Sichuan Paleouplift,which is expected to be an important target of risk exploration in the next step.
作者
文龙
谢继容
罗冰
周刚
张本健
严威
易海永
杨岱林
蒋航
田兴旺
姚军
谭秀成
许强
唐浩
WEN Long;XIE Jirong;LUO Bing;ZHOU Gang;ZHANG Benjian;YAN Wei;YI Haiyong;YANG Dailin;JIANG Hang;TIAN Xingwang;YAO Jun;TAN Xiucheng;XU Qiang;TANG Hao(PetroChina Southwest Oil&Gasfield Company,Chengdu,Sichuan 610051,China;Exploration and Development Research Institute,PetroChina Southwest Oil&Gasfield Company,Chengdu,Sichuan 610051,China;China Southern Petroleum Exploration&Development Corporation,Haikou,Hainan 571127,China;PetroChina Research Institute of Petroleum Exploration&Development-Northwest,Lanzhou,Gansu 730030,China;Southwest Petroleum University,Chengdu,Sichuan 610500,China)
出处
《天然气工业》
EI
CAS
CSCD
北大核心
2024年第12期1-14,共14页
Natural Gas Industry
基金
国家自然科学基金项目“扬子西北缘早古生代海相盆地多幕次构造—沉积转换及其成烃成储响应”(编号:U2344209)
中国石油—西南石油大学创新联合体科技合作项目“深层/超深层碳酸盐岩天然气勘探开发基础理论与关键技术研究”(编号:2020CX010000)
中国石油西南油气田公司科研项目“川西南部及周缘地区晚奥陶世岩相古地理格局及有利相带展布研究”(编号:20230301-03)
“四川盆地中西部震旦—石炭系油气成藏主控因素与分布规律研究”(编号:2024D101-04)。
关键词
四川盆地
奥陶系
宝塔组
大箐组
储层
白云岩
白云石化
Sichuan Basin
Ordovician
Baota Formation
Daqing Formation
Reservoir
Dolomite
Dolomitization