Classification and characteristics of source-reservoir interlayer and its controlling effect on oil-gas enrichment in continental tight reservoir
At present,it is considered that the accumulation of tight oil is characterized by source-reservoir integration or large-scale near-source distribution.However,the exploration practice indicates that the sweet spots near high-quality source rocks in continen-tal tight oil areas in China generally contain no oil or even produce a large amount of water.Therefore,it is necessary to re-recognize the sweet spots where tight oil is enriched.Based on systematically summarizing the classification scheme and geneses of the existing source-reservoir interlayer,as well as a large amount of core observations,the source-reservoir interlayer is divided into three types,i.e.,argillaceous interlayer,tight sandstone with argillaceous laminae,and sand-shale transition section,of which the physical prop-erties,distribution and logging response characteristics are described separately.The study suggests that the tight oil accumulation is mainly driven by the expansive force generated as a result of the hydrocarbon generation pressurization of source rock.When the charging resistance is greater than the expansive force,it is not conducive to oil-gas accumulation.Quantitative characterization shows that the thickness,transverse continuity and fracture development of source-reservoir interlayer jointly control the charging resistance and affect the barrier capacity of source-reservoir interlayer.Based on this,four pool-controlling modes for tight oil enrich-ment in the source-reservoir interlayer are established as follows.(1)When the thickness of the source-reservoir interlayer is smaller than the effective barrier thickness,the oil and gas will break through the barrier and continue to migrate.(2)When the extension radius of the source-reservoir interlayer is smaller than the radius of the affected area,the oil and gas can break through from the edge area and form a radial oil-gas accumulation zone.(3)When the thickness of the source-reservoir interval is greater than the ef-fective barrier thickness and the extension radius is greater than the radius of the affected area,oil and gas migration can be effective-ly blocked,resulting in the phenomenon of"sand without oil"in local areas.(4)When cracks are developed in the source-reservoir interlayer,the barrier capacity will be reduced,making it easier for oil and gas to break through.In conclusion,these research re-sults and understandings are expected to improve the theoretical basis of continental tight oil in China and provide theoretical guidance for the exploration and development of continental tight oil in China.
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