Genetic Classification,Characteristics and Hydrocarbon Occurrence of Small-scale Petroliferous Basins
Sedimentary basins are widely distributed on Earth.Among them,the small basins account for their majority.In China,small basins account for over 80%of the total number of basins,while in aspect of the industrial oil and gas reservoirs,the small-scale basins contribute less than 10%which is far less than large and medium-sized basins(＞76%).However,the hydrocarbon abundances per unit area(HAPUA)of most small-scale petroliferous basins are high;for some basins characterized by"small but enriched",the HAPUAs are much higher than large-to medium-sized petroliferous basins,resulting in higher exploration effectiveness.A comprehensive study of 16 small-scale basins containing conventional oil and gas in China was implemented.They are divided into remnant and proto small-scale basins based on the differences in basin formation mechanisms and dynamic environments.Furthermore,the proto small-scale basins are subdivided into strike-slip basin,rift basin,and thermal basin.Remnant small-scale petroliferous basins generally undergo three imperative evolutionary stages,including the proto-basin construction stage with development of the main source rock,the reformed and remnant stage,and the late buried and hydrocarbon generation stage.The residual source rocks in the proto-basin provide a resource foundation,and the deep burial in the late stage is the key link for hydrocarbon generation and accumulation.The three subtypes of proto small-scale basins,strike-slip,rift,and thermal basins,are all formed and developed in relatively active dynamic environments.They are generally characterized by rapid subsidence and deposition,relatively high geothermal fields,active deep background,and later-stage modification.This dynamic environment results deposition of"small but thick"strata in the basin and forms various structural traps.It also benefits the extraordinary growth and prosperity of organisms,the formation of high-quality source rocks,and hydrocarbon generation and accumulation.There are similarities between the"small but rich"petroliferous basins and the"small rock bodies forming large ore deposits"in terms of the formation dynamic environment and ore-forming theory.The two fields can be compared and mutually referenced in scientific research and academic thinking.
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