Characteristics of silty laminae in Zhangjiatan Shale of sou

Characteristics of silty laminae in Zhangjiatan Shale of southeastern Ordos Basin, China:Implications for shale gas formation

Yuhong Lei,Xiaorong Luo,Xiangzeng Wang,

Lixia Zhang,Chengfu Jiang,Wan Yang,Yuxi Yu, Ming Cheng,and Likuan Zhang

A B S T RA C T

Shale oil and gas have been discovered in the lacustrine organic-rich Zhangjiatan Shale of the Upper Triassic Yanchang Formation,Ordos Basin,China.Core observations indicate abun-dant silty laminae in the producing shales.This study documents the stratigraphic distribution of silty laminae and their relationship with interlaminated clay laminae.The type,structure,and charac-teristics of pores and mineral composition of silty laminae were observed and analyzed through thin section and scanning electron microscopy,X-ray diffraction,low-pressure CO2and N2adsorp-tion,mercury porosimetry,and helium pycnometry.Results from silty laminae are compared with those of clayey laminae.The fre-quency and thickness of silty laminae vary over a wide range.The thickness ranges from0.2to4mm and is1.5mm on average;the frequency ranges from4to32laminae/m and is23laminae/m on average.The thickness percentage of silty laminae in the mea-sured segments ranges from6%to17%.Silty laminae consist of quartz,feldspar,mixed-layer montmorillonite,and chlorite.In comparison to clayey laminae,non-clay detrital grains are larger, quartz and feldspar are more common,and clay minerals are less abundant.Pores in silty laminae are primary interparticle,dis-solutional,intercrystalline,and microfracture types.Mesopores (2–50nm in diameter)and macropores(50nm–1μm)are common,whereas,microporese<2nmTare rare;the distribution of pore diameters is multimodal.However,microscopic pores with a diameter commonly smaller than100nm are common in Copyright?2015.The American Association of Petroleum Geologists.All rights reserved. Manuscript received April3,2014;provisional acceptance July11,2014;revised manuscript received September8,2014;final acceptance September30,2014.

DOI:10.1306/0930*******A U T H O R S

Yuhong Lei～Key Laboratory of Petroleum Resources Research,Institute of Geology and Geophysics,Chinese Academy of Sciences, Beijing100029,China;granulitelei@04df3af9be23482fb4da4cae Yuhong Lei is a postdoctoral researcher at the Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing.He received B.S. and M.S.degrees in mineralogy,petrology,and mineral deposit geology from the China University of Geosciences and a Ph.D.in petroleum geology from the Institute of Geology and Geophysics Chinese Academy of Sciences.His interests include hydrocarbon migration in petroleum systems and unconventional oil and gas. Xiaorong Luo～Key Laboratory of Petroleum Resources Research,Institute of Geology and Geophysics,Chinese Academy of Sciences, Beijing100029,China;luoxr@04df3af9be23482fb4da4cae Xiaorong Luo is a research scientist in the Chinese Academy of Sciences and has

B.S.and M.S.degrees in geology from Northwestern University,China,and a

Ph.D.in geophysics from the University of Montpellier,France.His research in the

last30years has been in petroleum geology, currently focusing on numerical modeling,fluid pressure,and hydrocarbon migration and accumulation.

Xiangzeng Wang～Shaanxi Yanchang Petroleum(Group)Co.,Ltd.,75#Keji2Road, Xi’an710075,Shaanxi Province,China; sxycpcwxz@04df3af9be23482fb4da4cae

Xiangzeng Wang received his doctoral degree from School of Energy and Resources of China University of Geoscience.He is currently the vice president of Shaanxi Yanchang Petroleum (Group)Co.,Ltd.He has been involved in oil and gas exploration and exploitation for more than20 years.His main work in recent years has focused on the Ordos Basin.

Lixia Zhang～Shaanxi Yanchang Petroleum (Group)Co.,Ltd.,75#Keji2Road,Xi’an710075, Shaanxi Province,China;zlxcyq999@04df3af9be23482fb4da4cae Lixia Zhang received her bachelor’s degree from Northwest University.She is currently the vice president of Research Institute of Shaanxi Yanchang Petroleum(Group)Co.,Ltd.She has been involved in oil and gas exploration and exploitation for more than30years.Her main work in recent years has focused on shale gas exploration and exploitation.

AAPG Bulletin,v.99,no.4(April2015),pp.661–687661

clayey laminae.Thus,pore volume and surface area of micropores in silty laminae are less than those in the adjacent clayey laminae,and vice versa for meso-and macropores.The porosity of shales increases with the proportion of silty laminae in the shales.The silty laminae provide the storage space and flow conduit for oil and gas,and they play a significant role in the migration,accumu-lation,occurrence,and amount of gas in the shales.INTRODUCTION Shale gas refers to unconventional natural gas in organic-rich mud rocks (Curtis,2002).Shale gas reservoirs are widespread and contain a large amount of oil and gas reserve,which is difficult to produce using conventional technology (Curtis,2002).The success of shale gas exploration in the United States has encour-aged similar exploration activities in many other countries.In the last few years,China has experimented with shale gas exploration and made some major discoveries (Guo et al.,2011;Wang et al.,2011;C.F.Jiang et al.,2013a).The discovery in Zhangjiatan Shale,which is the shale in the lower part of Member 7of the Upper Triassic Yanchang Formation in southeastern Ordos Basin,is representative of those in lacustrine shales (C.F.Jiang et al.,2013a).Compared to sandstones,our understanding of the sedimentary characteristics of shale,such as grain composition,sedimentary tex-ture,and pores is limited (Passey et al.,2010;J.C.Zhang et al.,2011).Recently,many studies have been carried out as spurred by shale oil and gas exploration (e.g.,Curtis,2002;Bowker,2007;Passey et al.,2010),focusing on depositional environments (Kemp,1996;Loucks et al.,2007),organic content (Passey et al.,19 …… 此处隐藏：57078字，全部文档内容请下载后查看。喜欢就下载吧 ……