New understandings on gas accumulation and major exploration breakthroughs in subsalt Ma 4 Member of Ordovician Majiagou Formation,Ordos Basin,NW China  

作　　者：HE Haiqing GUO Xujie ZHAO Zhenyu XI Shengli WANG Jufeng SONG Wei REN Junfeng WU Xingning BI He 

机构地区：[1]PetroChina Exploration&Production Company,Beijing 100007,China [2]PetroChina Research Institute of Petroleum Exploration&Development,Beijing 100083,China [3]PetroChina Changqing Oilfield Company,Xi'an 710018,China

出　　处：《Petroleum Exploration and Development》2022年第3期489-501,共13页石油勘探与开发（英文版）

基　　金：Supported by the Scientific Research and Technology Development Project of PetroChina。

摘　　要：Geological conditions and main controlling factors of gas accumulation in subsalt Ma 4 Member of Ordovician Majiagou Formation are examined based on large amounts of drilling,logging and seismic data.The new understandings on the control of paleo-uplift over facies,reservoirs and accumulations are reached:(1)During the sedimentary period of Majiagou Formation,the central paleo-uplift divided the North China Sea in central-eastern of the basin from the Qinqi Sea at southwest margin of the basin,and controlled the deposition of the thick hummocky grain beach facies dolomite on platform margin of Ma 4 Member.Under the influence of the evolution of the central paleo-uplift,the frame of two uplifts alternate with two sags was formed in the central-eastern part of the basin,dolomite of inner-platform beach facies developed in the underwater low-uplift zones,and marl developed in the low-lying areas between uplifts.(2)From the central paleo-uplift to the east margin of the basin,the dolomite in the Ma 4 Member gradually becomes thinner and turns into limestone.The lateral sealing of the limestone sedimentary facies transition zone gives rise to a large dolomite lithological trap.(3)During the late Caledonian,the basin was uplifted as a whole,and the central paleo-uplift was exposed and denuded to various degrees;high-quality Upper Paleozoic Carboniferous-Permian coal measures source rocks deposited on the paleo-uplift in an area of 60000 km^(2),providing large-scale hydrocarbon for the dolomite lithological traps in the underlying Ma 4 Member.(4)During the Indosinian-Yanshanian stage,the basin tilted westwards,and central paleo-uplift depressed into an efficient hydrocarbon supply window.The gas from the Upper Paleozoic source rock migrated through the high porosity and permeability dolomite in the central paleo-uplift to and accumulated in the updip high part;meanwhile,the subsalt marine source rock supplied gas through the Caledonian faults and micro-fractures as a significant supplementary.Under the guidance of the a

关 键 词：Ordos Basin ORDOVICIAN subsalt Majiagou Formation central paleo-uplift lithological transition zone gas accumulation Well Mitan1 

分 类 号：P618.13[天文地球—矿床学]