Late Mesozoic volcanic activities of the Songliao Basin, NE China: Implications for Volcanic Hydrocarbon Reservoirs
Meng, Fanchao; Liu, Jiaqi; Cui, Yan
The Qingshen Volcanic rocks gas field, with over 100 billion cubic meters (bcms) of proven gas reserves, was discovered recently in the Songliao Basin, Northeastern China. The gas sources are mainly from the Upper Jurassic-Lower Cretaceous coal and associated dark mudstones, with minor inorganic sources. The reservoirs consist mainly of volcanic rocks. Whether did the Late Mesozoic magmatism have actively influence the source maturity and gas accumulation? The relationship between volcanism periods and the time of gas generation/accumulation must be studied at least.
Twenty samples, mainly rhyolite and rhyolitic tuff, from Yingcheng Formation of Songliao Basin were subjected to K/Ar dating. Combining with more than 150 samples dates from other authors, Late Mesozoic volcanic activities were divided two periods in Songliao Basin, Concentrating in 135~120Ma and 120~105Ma which constitute Huoshiling and Yingcheng Formation, respectively, while the source rocks of coal and associated mudstone were generating hydrocarbons. Volcanism are benefit for source maturity and growing hydrocarbon because of three reasons: Temperature. Volcanisms can make organic matter rapidly get to the hydrocarbon generation threshold; Catalyst. Metals in minerals not only promote matter thermal degradation, but also are catalysts of Fischer-Tropsch synthesis; Volcanic gases. The volcanic gases can promote source rocks maturity and become the carrier of petroleum.
Homogenization temperature of aqueous inclusions associated with hydrocarbon inclusions in volcanic reservoirs are divided into three phases. Results of basin modeling suggest the time of the gas accumulation was mainly around 100~65Ma, latter than the main period of Late Mesozoic volcanism. It is advantaged for gas pools accumulation, because volcanisms can make migration pathway and volcanic rocks are good reservoirs. The volcanism didn't destroy the gas reservoirs. Furthermore, the volcanic rocks are very good reservoirs. The porosity of volcanic reservoirs includes primary porosity such as gas voids, vesicles and intergrain pores, secondary porosity like intra-crystalline dissolution, fractures, weathering cracks, matrix dissolution and interstices. The quality of volcanic rock reservoirs in mainly controlled by lithofacies, weathering and structures. The best reservoirs are usually fromed near the top of volcanic eruption periods. Volcanic rock reservoirs is becoming one of the most unconventional oil gas resources.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013