Accumulation conditions and exploration directions of Ordovician lower assemblage natural gas, Ordos Basin, NW China  

作　　者：XU Wanglin LI Jianzhong LIU Xinshe LI Ningxi ZHANG Caili ZHANG Yueqiao FU Ling BAI Ying HUANG Zhengliang GAO Jianrong SUN Yuanshi SONG Wei 

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

出　　处：《Petroleum Exploration and Development》2021年第3期641-654,共14页石油勘探与开发（英文版）

基　　金：Supported by the National Key R&D Program of China(2017YFC0603106);National Petroleum Science and Technology Major Project(2016ZX05004-006);Science and Technology Project of PetroChina Exploration and Production Company(kt20180401)。

摘　　要：Based on drilling cores, well logging and seismic data, source rocks and reservoirs are evaluated;and the natural gas genesis is identified through the analysis of natural gas isotopes, components and fluid inclusions, to study the gas accumulation conditions of the gypsum salt rock related strata of the Ordovician lower assemblage in Ordos Basin.(1) The natural gas from Ordovician lower assemblage is high thermal evolution dry gas from marine source rock, characterized by relatively light δ^(13)C value of methane and heavy δ^(13)C value of ethane. The natural gas is identified as gas cracking from crude oil according to component analysis. Thermochemical sulfate reduction(TSR) reaction has happened between the hydrocarbon fluid and sulfate as sulfur crystals are found in the cores, hydrogen sulfide is found in the natural gas, and hydrocarbon and hydrogen sulfide fluid inclusions are widespread in secondary minerals.(2) Around the gypsum-salt lows, argillaceous rocks are extensive in the Ordovician lower assemblage, reaching a cumulative thickness of 20–80 m. The effective source rocks include argillaceous rock rich in organic laminae, algal clump and algal dolomite. Analysis shows that the source rocks have a dominant TOC of 0.1%–0.5%, 0.31% on average and 3.24% at maximum. The source rocks have an average TOC of 0.58% after recovered through organic acid salt method, indicating the source rocks have high hydrocarbon supply potential.(3) In the sedimentary period, the palaeo-uplift controlled the distribution of reservoirs. The inherited secondary palaeo-uplift in Wushenqi–Jingbian east of the central palaeo-uplift and the low uplift formed by thick salt rocks near Shenmu–Zizhou area controlled the distribution of penecontemporaneous grain shoal dolomite reservoirs. The salinization sedimentary environment of gypsum salt rock can promote the development of reservoir. There are three types of dolomite reservoirs, the one with intercrystalline pore, with dissolution pore, and with fracture;intercrystall

关 键 词：Ordos Basin Ordovician lower assemblage gypsum-salt rock marine source rock dolomite reservoir natural gas accumulation 

分 类 号：P618.13[天文地球—矿床学]