泰国呵叻盆地腹部二叠系碳酸盐岩台地前缘沉积模式

(1.陕西煤业化工技术研究院有限责任公司,陕西 西安 710075; 2.陕西延长石油(集团)有限公司研究院,陕西 西安 710065; 3.中石化海洋石油工程有限公司 上海物探分公司,上海 201208)

呵叻盆地,二叠系,碳酸盐岩,微量元素,沉积相

Sedimentary model of Permian carbonate platform margin in central Khorat Basin,Tailand
TONG Min-bo1,GAO Dong-chen2,CAO Qing-rong2,ZHANG Ying-chun3, LIU Ke2,ZHANG Li-yuan2

(1.Shaanxi Coal Chemical Industry Technology Research Institute Co.,Ltd.,Xi'an 710070, China; 2.Research Institute of Shaanxi Yanchang Petroleum(Group)Co.,Ltd.,Xi'an 710065,China; 3.Shanghai Geophysical Branch,Sinopec Offshore ServicesCompany,Shanghai 201208, China)

Khorat Basin; Permian; carbonate; microelement; sedimentary facies

DOI: 10.13800/j.cnki.xakjdxxb.2020.0304

备注

呵叻盆地是泰国陆上最大的含气盆地,是在印支板块稳定基底上发展起来的克拉通内部盆地。二叠系Pha Nok Khao组碳酸盐岩为晚古生代盆地初始构造拉张期产物,以浅海相碳酸盐岩沉积为主,是盆地内主要的天然气储层。通过分析δ13C,δ18O,Sr/Ba,B,V/(V+Ni)、Mn等地化指标,从而探讨古盐度、氧化还原条件、古水深等信息,认为Pha Nok Khao组碳酸盐岩为海相沉积,处于缺氧、弱氧化-弱还原环境,沉积时水体相对较深。岩石薄片和古生物鉴定、岩相标志分析,表明Pha Nok Khao组碳酸盐岩沉积以泥晶灰岩、泥晶白云岩、生屑灰岩等细粒成分为主,古生物多生活在热带-亚热带浅海环境中,其中P1井岩心呈现深灰-灰黑色、受滑塌作用形成了少量滑塌角砾岩,揭示了碳酸盐台地前缘斜坡相沉积特征。结合测井相分析了二叠系碳酸盐岩沉积时总体的水体深度变化,共识别出两期沉积旋回,将碳酸盐台地前缘沉积可划分为碳酸盐岩台地前缘斜坡和缓坡两个亚相。综上所述,建立了研究区二叠系Pha Nok Khao组碳酸盐台地前缘斜坡-缓坡相沉积模式,其中缓坡沉积相带对天然气聚集较为有利。

The largest onshore gas bearing basin of Thailand.The khorat Basin is a carton basin developed in the stable basement of the Indochina plate.The Permian carbonates of Pha Nok Khao formation are the initial tectonic extensional products of the late Paleozoic basins,mainly marine carbonate deposits,and are the main natural gas reservoirs in the basin.In this paper,an analysis of geochemical indicators was made to examine paleo salinity,redox conditions,ancient water depth,such as δ13C,δ18O,Sr /Ba,B,V/(V+Ni),Mn,confirming that the carbonates of Pha Nok Khao formation are marine sedimentation in a hypoxia and weak redox environment,and the water is relatively deep during deposition.A detailed analysis of rock silce,paleontology identification and lithofacies marker shows that the Permian carbonate rocks of Pha Nok Khao formation are mainly composed of micrite,micritic dolomite,and bioclastic limestone.Paleontology lives in the tropic to sub-tropic shallow sea environment.The core of P1 well shows dark gray and gray black,and a few of breccia is formed by slumping action,so the P1 well is for carbonate platform margin sedimentary facies.With the logging facies in view,it analyses the overall water depth change during Permian carbonate deposition,and identifies two sedimentary cycles.The carbonate platform margin sediments can be divided into two subfacies: foreslope and gentle slope.Accordingly sedimentary model of foreslope and gentle slope facies has been established in Permian carbonate platform margin of Pha Nok Khao formation,in which gentle slope sedimentary facies belts are more favorable for gas accumulation.