Comparison between Marine Shales and Lacustrine Shales in China
Jiang, Shu; Dahdah, Nick; Pahnke, Peter; Zhang, Jinchuan
The thorough study of Pre-Cambrian to Quaternary shales in China indicates marine shales have tremendous shale gas potential and lacustrine shales in China have huge both shale oil and shale gas potential. Thick prospective marine shales were widely deposited during sea level rise period in the shelf to basinal settings in the Yangtze platform region including Sichuan Basin and Tarim Basin from Pre-Cambrian Sinian to Silurian. Potential lacustrine shales were mainly developed in pro-delta setting of many basins scattered in China during basin rifting or post-rift high lake level period since late Permian. Both these marine and lacustrine shales are proven source rocks with high TOC (usually >2%). In terms of mineralogy, the quartz rich marine shales in China are remarkably alike Barnett shale, the lacustrine shales have higher clay mineral content and many contain swelling smectite and I/S mix layers when comparing with marine shales. As for the porosity and permeability, micro-pores and intra-organic nano-pores were observed from both marine and lacustrine shales, it seems the marine shale reservoir is tighter even marine shales have more intra-organic pores than lacustrine ones. All the organic rich marine shales e.g. Cambrian to Silurian shales in Sichuan Basin in China are in dry gas window and are emerging thermogenic shale gas plays. The Mesozoic lacustrine shales with high TOC and medium Ro (wet gas window) can be thermogenic shale gas plays based on recent drilling for Triassic Yanchang7 shale in Ordos Basin and Jurassic Daanzhai shale in Sichuan Basin. Most Meso-Cenozoic shales (e.g. Triassic Yanchang7 shale in Ordos basin, Paleogene Shahejie3 shale in Bohai Bay Basin) are in oil window and have shale oil potential. Since both marine and lacustrine basins in China experienced complex tectonic/structural activities, which could cause the leak of ancient shale gas and shale oil reservoirs, exploration should be focused in relative tectonic stable regions.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013