银额盆地重点凹陷下白垩统碎屑岩储层发育特征与成储机制OA

Lower Cretaceous clastic hydrocarbon reservoirs in the Yin'gen-Ejinaqi Basin constitute the key explo-ration targets of Zhongyuan Oilfield.However,inadequate research on reservoir development characteristics and reservoir-forming mechanisms has hindered in-depth exploration progress.By integrating multiple analytical methods including thin section observation,scanning electron microscopy,fluid inclusion analysis,and reservoir physical property testing,a systematic comparative study was carried out on the Chagan Sag and Guaizihu Sag of Yin'gen-Ejinaqi Basin.Lithologies within the study area are predominantly lithic feldspar sandstone and feldspathic lithic sandstone.The reservoirs in the Chagan Sag generally exhibit lower compositional maturity than those in the Guaizihu Sag.Moreover,reservoir pore space and physical properties differ drastically among various strata,a phe-nomenon primarily reflected by divergent reservoir-forming mechanisms corresponding to two major depositional intervals.During the deposition of the Lower Cretaceous Suhongtu Formation,the Chagan Sag was subjected to the thermal baking-catalysis effect of volcanic rocks,which accelerated hydrocarbon generation and organic acid expulsion from source rocks.Plentiful organic acids dissolved labile volcanic rock fragments and produced abundant secondary dissolution pores.Meanwhile,early hydrocarbon charging suppressed carbonate cementation,collec-tively yielding favorable overall reservoir physical properties.In comparison,the Guaizihu Sag experienced no volcanic activity during this interval.Therefore,its source rocks experienced delayed hydrocarbon generation and organic acid expulsion,accompanied by low-efficiency hydrocarbon emplacement.These processes failed to effec-tively ameliorate reservoir quality,resulting in poorer physical properties relative to the Chagan Sag.During the deposition of the Lower cretaceous Bayingobi Formation,the Guaizihu Sag developed a rigid grain-dominated provenance,with a sediment transport pattern characterized by proximity to boundary faults yet long distance from the provenance area.Combined with intense fluid overpressure developed during burial,these factors jointly laid favorable foundations for high-quality reservoirs,which possessed superior overall physical properties.In con-trast,the Chagan Sag was governed by mixed grain provenance,a transport pattern with boundary faults adjacent to proximal provenance areas,and normal-pressure fluid conditions throughout burial.Consequently,its reservoirs exhibited inferior overall physical properties compared with the Guaizihu Sag.