Discovery of unconventional oil and gas in volcanic sedimentary basins around Songliao and its enlightenment:Take Shuangyang Basin as an example

Conventional oil and gas exploration and development in the Songliao basin has entered the middle and late stage,and the subsequent replacement resources are insufficient.Oil and gas exploration needs to be expanded to peripheral new areas,new strata and new types.In this study,the unconventional oil and gas geological conditions of the Shuangyang basin in the east of the periphery of the Songliao basin were comprehensively investigated and studied by means of three-dimensional high-precision gravity,magnetoelectric exploration and the drilling of oil and gas parameter wells,combined with high-precision zircon ²⁰⁶Pb/²³⁸U dating,organic geochemical test,XRD mineral composition determination and nuclear magnetic property analysis.The results show that the complete Carboniferous Permian Cretaceous stratigraphic sequence was developed in the Shuangyang basin,which was divided into nine sets of physical property combinations,and there were two sets of clastic sedimentary strata with low density,low resistivity and low magnetization.After drilling verification,two sets of dark shale strata were found in the Shuangyang basin outside the Songliao basin.According to the comprehensive stratigraphic ratio and zircon age,the ages of the two sets of shale strata are the lower Cretaceous Chang’an formation and the Triassic Damaogang formation respectively.Among them,the shale of Chang’an formation has high abundance of organic matter,average TOC content of 1.63%,average hydrocarbon generation potential S₁+S₂ of 1.21 mg/g,organic matter dominated by Ⅱ₁ and Ⅱ₂ kerogen,R_o of 0.55%-0.95%,medium low thermal evolution degree,average nuclear magnetic effective porosity of 4.5%,and average brittle mineral content of 59%.It has good reservoir and compressibility and is a favorable tight oil Shale oil-enriched strata.The organic matter abundance of shales in the Damaotan formation is medium,the average TOC content is 1.52%,the average value of hydrocarbon generation potential S₁+S₂ is 0.35 mg/g,the organic matter is mainly type Ⅱ₂ and Ⅲ kerogen,the R_o is in the range of 1.59%-2.64%,it is in the high maturity over maturity evolution stage,the average value of nuclear magnetic effective porosity is 3.3%,and the average content of brittle minerals is 56%,which is a favorable CBM and shale gas enrichment layer series.According to the preliminary analysis of lithologic assemblage and basic characteristics of oil and gas enrichment,the formation of the above two sets of favorable shale series is closely related to volcanic activity.The 39 sedimentary basins developed in the east of the periphery of the Songliao basin also have the sedimentary characteristics of faulted lake basins during volcanic activity.It is speculated that they have the material basis and geological conditions for unconventional oil and gas formation and enrichment.It indicates that the eastern basin group in the periphery of the Songliao has unconventional oil and gas exploration prospects.