Origin of the penecontemporaneous sucrosic dolomite in the Permian Qixia Formation, northwestern Sichuan Basin, SW China  

作　　者：LU Feifan TAN Xiucheng ZHONG Yuan LUO Bing ZHANG Benjian ZHANG Ya LI Minglong XIAO Di WANG Xiaofang ZENG Wei 

机构地区：[1]State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu 610500,China [2]Department of Key Laboratory of Carbonate Reservoirs of CNPC,Southwest Petroleum University,Chengdu 610500,China [3]Institute of Petroleum Exploration and Exploitation,PetroChina Southwest Oil and Gas Field Company,Chengdu 610041,China [4]Northwest Sichuan Gas Mine,PetroChina Southwest Oil and Gas Field Company,Jiangyou 621741,China [5]Key Laboratory of Surficial Geochemistry,Ministry of Education,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China [6]PetroChina Hangzhou Institute of Petroleum Geology,Hangzhou 310023,China

出　　处：《Petroleum Exploration and Development》2020年第6期1218-1234,共17页石油勘探与开发（英文版）

基　　金：Supported by the National Science&Technology Major Project of China(2016ZX05004002-001);Natural Science Foundation(41802147);Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance

摘　　要：The characteristics,formation time,and origin of the sucrosic dolomite reservoirs in the Permian Qixia Formation of northwestern Sichuan Basin are analyzed.Core and outcrop description and microscopic analysis of the sucrosic dolomite samples are carried out.It is found that the dolomite has typical features different from other kinds of dolomites:(1)This dolomite is generally medium-coarse in crystal size,and often associated with very finely to finely crystalline dolomite and cave-filling dolomite.(2)Typical identification marks of eogenetic karstification are developed at the top of the upward-shallowing sequence.(3)The medium-coarse crystalline sucrosic dolomite is cut by the early diagenetic karst fabric,and is characterized by dolomite with dissolution edge,dolomite vadose silt in pores,and transgression clay filling between the medium-coarse dolomite crystals.The medium-coarse crystalline sucrosic dolomite was formed earlier than the eogenetic karstification.The sucrosic dolomite with occasional cloudy core and clear rim has bright cathodoluminescence,high inclusions temperature,significant negative skewness carbon and oxygen isotopic compositions,and rare-earth element(REE)pattern similar to seawater,indicating it experienced two periods of dolomitization,evaporative concentration reflux-infiltration and penecontemporaneous seawater circulation hydrothermal fluid dolomitization.The study results not only update the understanding on the dolomitization time of Qixia Formation,demonstrate that the sucrosic dolomite can be formed in the penecontemporaneous stage when seawater reflux superimposed with hydrothermal fluid effects,but also show that the taphorogenesis in the Dongwu period began in the Early Permian.Moreover,the dolomite controlled by the grain bank migration and terrain in the slope break appears in bands of large scale,this knowledge provides basis for expanding the exploration field of this type of reservoirs.

关 键 词：sucrosic dolomite penecontemporaneous dolomitization seawater cyclic hydrothermal fluid eogenetic karstification Qixia Formation PERMIAN Sichuan Basin 

分 类 号：P618.13[天文地球—矿床学] P588.245[天文地球—地质学]