Porosity distribution in cyclic dolomites of the Lower Qiulitag Group(Upper Cambrian)in northwestern Tarim Basin,China  

作　　者：Yan-qiu Zhang Zeng-hui Guo Dai-zhao Chen 

机构地区：[1]Development and Research Center of China Geological Survey,Ministry of Natural Resources,Beijing 100037,China [2]Key Laboratory of Petroleum Resources Research,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China [3]Institute of Earth and Environmental Science,University of Potsdam,Karl-Liebknecht-Str.24-25,14476 Potsdam-Golm,Germany

出　　处：《China Geology》2020年第3期425-444,共20页中国地质（英文）

基　　金：funded by geological survey projects of China Geological Survey(DD20190405,DD20190406);National Science and Technology Special Project of China(2011ZX0500803);National Basic Research Project(2012CB214802).

摘　　要：Increasing interests in hydrocarbon resources at depths have drawn greater attentions to the deeply-buried carbonate reservoirs in the Tarim Basin in China.In this study,the cyclic dolomite rocks of Upper Cambrian Lower Qiulitag Group from four outcrop sections in northwestern Tarim Basin were selected to investigate and evaluate the petrophysical properties in relation to depositional facies and cyclicity.The Lower Qiulitag Group includes ten lithofacies,which were deposited in intermediate to shallow subtidal,restricted shallow subtidal,intertidal,and supratidal environments on a carbonate ramp system.These lithofacies are vertically stacked into repeated shallowing-upward,meter-scale cycles which are further grouped into six third-order depositional sequences(Sq1 to Sq6).There are variable types of pore spaces in the Lower Qiulitag Group dolomite rocks,including interparticle,intraparticle,and fenestral pores of primary origin,inter crystal,and vuggy pores of late diagenetic modification.The porosity in the dolomites is generally facies-selective as that the microbially-originated thrombolites and stromatolites generally yield a relatively high porosity.In contrast,the high-energy ooidal grainstones generally have very low porosity.In this case,the microbialite-based peritidal cycles and peritidal cycle-dominated highstand(or regressive)successions have relatively high volumes of pore spaces,although highly fluctuating(or vertical inhomogeneous).Accordingly,the grainstone-based subtidal cycles and subtidal cycle-dominated transgressive successions generally yield extremely low porosity.This scenario indicates that porosity development and preservation in the thick dolomite successions are primarily controlled by depositional facies which were influenced by sea-level fluctuations of different orders and later diagenetic overprinting.

关 键 词：DOLOMITES POROSITY CYCLICITY Upper Cambrian STROMATOLITE Microbial build up Oil-gas basin Oil-gas exploration engineering Tarim Basin China 

分 类 号：P618.13[天文地球—矿床学]