Genesis of high-quality source rocks in volcano-related alkaline lakes and implications for the exploration and development of shale oil and gas

In order to clarify the controlling mechanisms of volcanic activities on the development of high-quality source rocks in non-marine petroliferous basins, this study summarizes the relationships between volcanic activity, alkaline lakes and high-quality source rocks through an extensive review of previous studies and proposes that alkaline lakes act as a vital link between volcanic activities and source rocks. It is suggested that large amount of CO2 emitted by volcanic activities would enter hydrothermal fluids, underground waters or rivers and then produce a large amount of HCO3- through accelerated silicate hydrolysis process, leading to the formation of alkaline lakes. The high pH in alkaline lakes would activate a variety of nutrient elements and compounds such as Mo, phosphate and silicate, thus improving the primary productivity of water body. In addition, the high pH also would lead to an exponential increase of silica solubility in alkaline waters. During the process of pH decrease by initial degradation of organic matter, the dissolved silica would precipitate and form a siliceous layer, which could effectively prevent further degradation of organic matter. Based on these assumptions, this study proposes a genetic model for volcanism-alkaline lake-high-quality source rocks chain, which is the main reason of the occurrence of brittle and porous shale reservoirs for oil due to a high content of microcrystalline dolomite and tuff materials that are easily converted from montmorillonite to zeolite, potassium feldspar, and sodium feldspar. © 2021, OIL & GAS GEOLOGY Editorial Board. All right reserved.