Sequence stratigraphy and its application in marine shale gas exploration: A case study of the Lower Silurian Longmaxi Formation in the Jiaoshiba shale gas field and its adjacent area in southeast Sichuan Basin, SW China

Abstract Based on outcrops, cores, well logs data, and mineralogical, geochemical and petrophysical analysis, we studied the sequence stratigraphy of marine shale dominated the Lower Silurian Longmaxi Formation, favorable commercial shale gas interval within the sequence stratigraphic framework. We interpret the Lower Member of the Longmaxi Formation as a third order sequence which is composed of transgressive systems tract (TST), early highstand systems tract (EHST) and late highstand systems tract (LHST). The TST mainly consists of mixed siliceous mudstone and clay-rich siliceous mudstone with high total organic carbon (TOC) content, high content of brittle minerals and the highest gas content which is the most favorable shale gas reservoir interval; the EHST is mainly composed of mixed siliceous mudstone and clay-rich siliceous mudstone in the lower part and mixed argillaceous mudstone in the upper part with well-developed laminaes, moderate TOC content and gas content; finally, the LHST is mainly composed of organic-lean and clay-rich mudstone (e.g. silica-rich argillaceous mudstone and mixed argillaceous mudstone) with the lowest gas content. Sequence stratigraphic framework controls the distribution of TOC, mineralogy in time and space, which further controls the sweet spot areally and pay zone vertically for shale gas accumulation in the southeast Sichuan Basin. The data collected from the commercial shale gas wells confirmed that the sequence stratigraphy is valid for the shale gas exploration and can be applied to the shale gas exploration in the other area.

[1]  C. Mitchell,et al.  Late Ordovician to earliest Silurian graptolite and brachiopod biozonation from the Yangtze region, South China, with a global correlation , 2000, Geological Magazine.

[2]  P. Jaiswal,et al.  Can seismic velocities predict sweet spots in the Woodford Shale? A case study from McNeff 2–28 Well, Grady County, Oklahoma , 2014 .

[3]  Hanrong Zhang,et al.  Formation and enrichment mode of Jiaoshiba shale gas field, Sichuan Basin , 2014 .

[4]  Chen Xu,et al.  HIRNANTIAN (LATEST ORDOVICIAN) GRAPTOLITES FROM THE UPPER YANGTZE REGION, CHINA , 2005 .

[5]  Fang Junhua.  Structure characteristics and accumulation significance of nanopores in Longmaxi shale gas reservoir in the southern Sichuan Basin , 2012 .

[6]  R. E. Martinez,et al.  Sequence Stratigraphy of Pliocene and Pleistocene Turbidite Systems, Northern Green Canyon and Ewing Bank (Offshore Louisiana), Northern Gulf of Mexico , 1998 .

[7]  Yang Jun-bin.  Source Rock Characteristics of Marine Strata,Sichuan Basin , 2011 .

[8]  O. Catuneanu.  Sequence stratigraphy of clastic systems: concepts, merits, and pitfalls , 2002 .

[9]  C. Brett,et al.  Mudrock sequence stratigraphy: A multi-proxy (sedimentological, paleobiological and geochemical) approach, Devonian Appalachian Basin , 2011 .

[10]  R. Slatt,et al.  Lithofacies and sequence stratigraphy of the Barnett Shale in east-central Fort Worth Basin, Texas , 2012 .

[11]  Liu Xinjin,et al.  Reservoir-forming conditions and favorable exploration zones of shale gas in Lower Silurian Longmaxi Formation of Sichuan Basin , 2010 .

[12]  W. E. Galloway,et al.  Towards the standardization of sequence stratigraphy , 2009 .

[13]  A. Miall.  Stratigraphic Sequences and Their Chronostratigraphic Correlation , 1991 .

[14]  G. P. Allen,et al.  Siliciclastic sequence stratigraphy; concepts and applications , 1999 .

[15]  Timothy R. Carr,et al.  Organic-rich Marcellus Shale lithofacies modeling and distribution pattern analysis in the Appalachian Basin , 2013 .

[16]  Cheryl A. Mnich,et al.  A sequence-stratigraphic framework for the Upper Devonian Woodford Shale, Permian Basin, west Texas , 2014 .

[17]  Chen Yanhui,et al.  Seismic prediction of sweet spots in the Da'anzhai shale play, Yuanba area, the Sichuan Basin , 2014 .

[18]  Shu Jiang,et al.  Heterogeneity of the Lower Silurian Longmaxi marine shale in the southeast Sichuan Basin of China , 2015 .

[19]  Zhang Jun-peng.  Sequence Stratigraphy of Silurian Black Shale and Its Distribution in the Southeast Area of Chongqing , 2012 .

[20]  Luo Yue,et al.  The geologic background of the Siluric shale-gas reservoiring in Szechwan, China , 2010 .

[21]  Zhaoping Meng,et al.  A preliminary study on the pore characterization of Lower Silurian black shales in the Chuandong Thrust Fold Belt, southwestern China using low pressure N2 adsorption and FE-SEM methods , 2013 .

[22]  C. Liang,et al.  Shale lithofacies and reservoir space of the Wufeng–Longmaxi Formation, Sichuan Basin, China , 2012 .

[23]  R. Slatt,et al.  Comparative sequence stratigraphy and organic geochemistry of gas shales: Commonality or coincidence? , 2012 .

[24]  J. Wagoner,et al.  Siliciclastic sequence stratigraphy in well logs, cores, and outcrops , 1990 .

[25]  Zhang Chang-jun.  Comparison of Silurian Longmaxi Formation shale of Sichuan Basin in China and Carboniferous Barnett Formation shale of Fort Worth Basin in United States , 2011 .

[26]  C. Mitchell,et al.  Ashgillian graptolite fauna of the Yangtze region and the biogeographical distribution of diversity in the latest Ordovician , 2003 .

[27]  Roger M. Slatt,et al.  Merging sequence stratigraphy and geomechanics for unconventional gas shales , 2011 .

[28]  Li Zhi-ming,et al.  Distribution of Black Shale in the Wufeng-Longmaxi Formations (Ordovician-Silurian),South China: Major Controlling Factors and Implications , 2007 .

[29]  J. Hower,et al.  High-resolution geochemistry and sequence stratigraphy of the Hushpuckney Shale (Swope Formation, eastern Kansas): implications for climato-environmental dynamics of the Late Pennsylvanian Midcontinent Seaway , 2004 .

[30]  Junhua Fang,et al.  Shale gas reservoir characterisation: A typical case in the southern Sichuan Basin of China , 2011 .

[31]  Rob L. Gawthorpe,et al.  High-Resolution Facies Analyses of Mudstones: Implications for Paleoenvironmental and Sequence Stratigraphic Interpretations of Offshore Ancient Mud-Dominated Successions , 2007 .

[32]  P. Weimer,et al.  Sequence-stratigraphic architectures and sand-body distribution in Cenozoic rifted lacustrine basins, east China , 2013 .

[33]  Wang Jia.  Shale gas exploration prospect of Lower Paleozoic in southeastern Sichuan and western Hubei-eastern Chongqing areas,China , 2011 .

[34]  W. Schlager.  Sedimentology and Sequence Stratigraphy of Reefs and Carbonate Platforms: A Short Course , 1992 .

[35]  Xiangliang Zeng,et al.  Characteristics of the Shale Gas Reservoir Rocks in the Lower Silurian Longmaxi Formation, East Sichuan Basin, China , 2013 .

[36]  T. Engelder,et al.  Sequence stratigraphy and depositional environments of the Shamokin (Union Springs) Member, Marcellus Formation, and associated strata in the middle Appalachian Basin , 2014 .