--> --> Abstract: Upper Ordovician-Lower Silurian Shale Gas Reservoirs in Southern Sichuan Basin, China, by Xinjing Li, Caineng Zou, Zhongjian Qiu, Jianzhong Li, Gengsheng Chen, Dazhong Dong, Lansheng Wang, Shiqian Wang, Zonggang Lu, Shejiao Wang, and Keming Cheng; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Upper Ordovician-Lower Silurian Shale Gas Reservoirs in Southern Sichuan Basin, China

Xinjing Li1; Caineng Zou1; Zhongjian Qiu2; Jianzhong Li1; Gengsheng Chen3; Dazhong Dong1; Lansheng Wang3; Shiqian Wang3; Zonggang Lu3; Shejiao Wang1; Keming Cheng1

(1) Research Institute of Petrochina Exploration and Development, Beijing, China (a href="mailto:[email protected]">[email protected]).

(2) China National Petroleum Corporation, Beijing, China.

(3) Petrochina Southwest Oil and Gas Field Company, Sichuan, China.

Extensive later Ordovician and initial early Silurian black marine shales are important Palaeozoic source rocks deposited in a partly restricted environment related to a worldwide transgression in Southern Sichuan Basin, Upper Yangzi platform, China. Lowermost Longmaxi Formation is organic-rich black graptolitic shale with subordinate limestone and siltstones overlain grey greenish shale and siltstone. Hirnantian Stage Kuanyinqiao Member between Longmaxi and Wufeng Formation preserves Hirnantia-Dalmanitina fauna in the marlstone and calcareous mudstone. Lower Silurian in Southwestern and Middle-Lower Silurian in Southeastern Sichuan Basin only remain for the erosion due to Caledonian movement.

The average total organic content of the target interval for shale gas is about 3 wt. % that is the consequence of hydrocarbon generation and expulsion during higher maturation (Ro 2.3-3.4%). Fieldworks in the Southern Sichuan provided some preliminary insight into the good potential for shale gas of lowermost Silurian ‘hot’ graptolitic shale. Widespread gas shows presented in Silurian Formation in drilled wells. In some cases, the elevated gamma-ray and resistivity values suggest the presence of the “hot” shale. The first shale gas exploration well further proves good gas content in the cored interval with a typical response on wireline logs. In addition, one of significant characteristics of Longmaxi target interval is that a great deal of micropores and nanopores are well developed in organic matter at higher maturity that the remaining hydrocarbon potential is almost zero, though its petrology, bioclasts layers, primary pore spaces and types are unique compared with those of Barnett shale in core area, Eagle Ford shale in outcrop and etc.. Moreover, Silurian “hot” shale and later Ordovician Wufeng Formation are enveloped by lower tight Baota Limestone, primary frac barriers. The grey greenish organically lean shale may be weak upper barrier.

Upper Ordovician-Lower Silurian shale analysis of logs, Pyrolysis, thin-sections, CL, QEMSCAN, XRD and XFD indicate that the vertical lithological variations and fabric anisotropy are notable, not only the clay (mainly illite ), carbonate, quartz and pyrite content, but the primary origin and geological evolution. Integrated data sets can be used to characterize several lithofaces units rather than a whole homogeneous unit as the porosity, permeability, geomechanical properties of “hot” shales can be related to the lithologies. We conclude that there is a strong potential of shale gas in southern Sichuan basin, despite it poses different challenges for the development of higher and over maturity black shale.