--> Abstract: Diagenesis of Deep Volcanic Reservoirs in the Songliao Basin, NE China, by Zihui Feng, Ying Tong, and Hongmei Shao; #90078 (2008)

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Diagenesis of Deep Volcanic Reservoirs in the Songliao Basin, NE China

Zihui Feng, Ying Tong, and Hongmei Shao
Daqing Oilfield Limited Company Exploration and Development Institute, Daqing, China

Significant gas discoveries have been made recently in the deep Upper Jurassic - Lower Cretaceous strata of the Songliao Basin, northeastern China. As the gas reservoirs consist mainly of volcanic rocks (rhyolite and tuff), a study of reservoir lithofacies and diagenesis is particularly important for locating high quality gas pays. Based on field survey and core analysis, five volcanic lithofacies can be identified, including volcanic conduit, eruption, effusion, invasion and volcanic sedimentary facies. These lithofacies reflect different stages of volcanic activities from initiation, development, to termination, and control the lithology and distribution of volcanic rock reservoirs. Results of core observation, thin section analysis and laser con-focus microscopic imaging indicate that the quality of volcanic rock reservoirs is controlled not only by their lithofacies, but also how these lithofacies were spatially combined. The difference in the pore types, development degrees and spatial combinations leads to different diagenetic patterns and hence different gas storage capacities. Principal diagenetic mechanisms include leaching and weathering of the volcanic rock surface, microfracturing formation due to tectonic stress after burial, and reservoir fabric corrosion by alkaline fluids from deep crust. Thus, high quality reservoirs occur most likely on the top of the volcanic rock surface, near paleotopogrphic highs and adjacent to major deep-seated faults.

 

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas