2019 AAPG Annual Convention and Exhibition:

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Calm Harbor Hypothesis: Chances for China’s Shale Gas Exploration in Structurally Complex Areas

Abstract

Shale gas attracts world wide attention for the glorious success in commercial exploitation in North America. China is thought to have equally or more abundant resources than the U.S.. However, the major of these resources lie in older and more mature shale under much more complex structural backgrounds, including Ordovician-Silurian Wufeng-Longmaxi Shales, Cambrian Niutitang shales, and Neoproterzoic Doushantuo shales of Eastern Sichuan Fold Belt (ESFB). The first commercial shale gas field outside North America, China’s Fuling Shale Gas Field (CFSGF), lies in an rhomboid faulted anticline of the Eastern Sichuan Fold Belt. CFSGF’s data prove that structurally complex backgrounds and high to over high maturity of gas shales really matter and may greatly hinder China’s shale gas exploration and exploitation. To overcome these limitations, besides organic types and contents, Ro, porosity, permeability, Si content and fractures, more attention were paid to tectonic evolution and structural characteristics. An integrated source of data were collected and analyzed, including 2-D and 3-D seismic data, uplift and exhumation dating data, outcrops and cores, exploration and production well data, etc. The multi-stage tectonic evolution were restored and the structural backgrounds were carefully characterized, especially for the Trough Fold Belt portion of the ESFB and adjacent areas, where gas shale experienced more complex and intense deformation of folding, faulting, uplift and erosion than the Comb Fold Belt. Advantageous shale gas targets were finally delineate. Shale gas wells AY1# and YY1# made significant breakthroughs with high production in Cambrian-Ordovician shales. Furthermore, Shale gas well YY1# obtained gas production in Neoproterzoic Doushantuo shales, which is the oldest shale gas reservoir yet discovered worldwide. These breakthroughs in severely eroded synclines and footwalls of thrust fault belts bring splendid prospects for the vast areas of structurally complex ESFB, which used to be considered unsuitable for exploration and thus exploitation. Therefore “Calm Harbor” hypothesis were proposed for shale gas exploration in structurally complex ESFB and adjacent areas. It means that relatively stable and less structurally complex parts among highly tectonic deformed areas are still possible advantageous targets for shale gas.