Petrologic characteristics and genetic model of lacustrine lamellar fine-grained rock and its significance for shale oil exploration: A case study of Permian Lucaogou Formation in Malang sag, Santanghu Basin, NW China

Abstract Taking the Permian Lucaogou Formation in the Malang sag, Santanghu Basin as an example, by using petrological methods such as high resolution core image scanning, conventional thin section, scanning electron microscope and energy spectrum analysis and geochemical tests such as trace elements and biomarker compounds, the petrologic features and sedimentary origin of the lamellar organic rich fine-grained rocks of lake facies were investigated, and its significance for shale oil and tight oil exploration was analyzed. The results of the study show that there are four types of laminae, siliciclastic enrichment laminae, carbonate enrichment laminae, tuffaceous enrichment laminae and organic matter enrichment laminae, which can form three kinds of layer combinations. Organic matter is laminar enrichment or dispersed in the carbonate laminae and tuff laminae. Stratification of ancient lake water was formed in the closed saline lake sedimentary systems with insufficient continental clast supply, and the activity of warm water at the lake bottom and the monsoon climate worked jointly to control enrichment of organic matter and formation of lacustrine lamina fine-grained rocks. This kind of fine-grained rocks have higher potential of hydrocarbon generation due to high abundance of organic matter, are rich in reservoir space due to the existence of micro-pores in carbonate laminae and micro-cracks between the laminae, and suitable for fracturing because of high brittle mineral content. They have favorable conditions for shale oil and tight oil accumulation, and are significant for exploration.

[1]  Jiang Zhen-xue.  Diagenetic evolution and formation mechanism of dissolved pore of shale oil reservoirs of Lucaogou formation in Malang sag , 2012 .

[2]  J. Mount.  Mixed siliciclastic and carbonate sediments: a proposed first-order textural and compositional classification , 1985 .

[3]  A. Cook,et al.  Classification of oil shales, coals and other organic-rich rocks , 1991 .

[4]  Liu Wen-hui.  The Discussion on Anoxic Environments and Its Geochemical Identifying Indices , 2004 .

[5]  Wang Pin-xian.  Algal Blooms: the Primary Mechanism in the Formation of Lacustrine Petroleum Source Rocks , 2001 .

[6]  Kent A. Bowker,et al.  The Barnett Shale Play, Fort Worth Basin , 2006 .

[7]  S. Calvert,et al.  Geochemistry of Recent oxic and anoxic marine sediments: Implications for the geological record , 1993 .

[8]  R. Zhou,et al.  Productivity of Eocene ancient lake and enrichment mechanism of organic matter in Huadian Basin , 2012 .

[9]  Jiang Zai-xin.  Several issues in sedimentological studies on hydrocarbon-bearing fine-grained sedimentary rocks , 2013 .

[10]  J. M. Mitchell,et al.  An Overview of Climatic Variability and its Causal Mechanisms , 1976, Quaternary Research.

[11]  D. Jarvie,et al.  Unconventional shale-gas systems: The Mississippian Barnett Shale of north-central Texas as one model for thermogenic shale-gas assessment , 2007 .

[12]  Xinning Li,et al.  Thermodynamic analyses of dolomite dissolution and prediction of the zones of secondary porosity: A case study of the tight tuffaceous dolomite reservoir of the second member, Permian Lucaogou Formation, Santanghu Basin, NW China , 2014 .

[13]  D. McKirdy,et al.  ORGANIC MATTER IN OIL SHALES , 1980 .

[14]  Andrew C. Aplin,et al.  Mudstone diversity: Origin and implications for source, seal, and reservoir properties in petroleum systems , 2011 .

[15]  C. Reservoirs.  Thermodynamic analyses of dolomite dissolution and prediction of the secondary porosity zones: A case study of tight tuffaceous dolomites of the second member, Permian Lucaogou Formation reservoir, Santanghu Basin, NW China , 2014 .

[16]  Zhao An-kun.  Sedimentary Records of Triassic Megamonsoon in Upper Yangtze Area , 2010 .

[17]  H. Schulz,et al.  A 5000-yr Record of Climate Change in Varved Sediments from the Oxygen Minimum Zone off Pakistan, Northeastern Arabian Sea , 1999, Quaternary Research.

[18]  Zhu Guang-you.  Geochemical Characteristics of Two Sets of Excellent Source Rocks in Dongying Depression , 2003 .

[19]  Li Pilong.  THE ORGANIC-RICH HYDROCARBON SOURCE ROCKS AND THEIR RESOURCE POTENTIALS IN JIYANG DEPRESSION , 2004 .

[20]  L. Håkanson,et al.  Sediment trap assemblages — a methodological description , 1989, Hydrobiologia.

[21]  M. Key,et al.  Organic Petrological Study on Hydrocarbon Generation and Expulsion from Organic-rich Black Shale and Oil Shale , 2006 .

[22]  Fan Ting-ting.  Permian Lacustrine Eruptive Hydrothermal Dolomites,Santanghu Basin,Xinjiang Province , 2010 .

[23]  W. J. Wade,et al.  Depositional Environments, Organic Carbon Accumulation, and Solar-Forcing Cyclicity in Smackover Formation Lime Mudstones, Northern Gulf Coast , 1997 .

[24]  P. O'sullivan.  Annually-laminated lake sediments and the study of Quaternary environmental changes — a review , 1983 .