Formation mechanisms of nano-scale pores/fissures and shale oil enrichment characteristics for Gulong shale,Songliao Basin
The Cretaceous Gulong shale oil reservoirs in the Songliao Basin are composed of organic-rich continental shales with high clay content,interbedded with minor amounts of thinly laminated calcareous sandstones and dolomites.Currently,there is a lack of studies on the pore-fissure system and shale oil enrichment pattern of these reservoirs.Based on the data from experiments and analyses including argon ion milling-field emission scanning electron microscopy(FE-SEM),energy-dispersive X-ray spectroscopy(EDS),high-pressure mercury injection analysis,low-temperature nitrogen adsorption experiment,fluorescence thin section observation,X-ray diffraction(XRD)mineralogy of whole rock,and geochemical analysis,we investigate the organic-inorganic pore-fissure system in the Gulong shale and its relationship with shale oil enrichment.The results are as follows:(1)The Gulong shale hosts a dual-porosity reservoir system consisting of matrix pores and microfissures.Matrix pores serve as shale oil enrichment spaces,while microfissures provide both storage spaces and seepage pathways for shale oil;(2)Influenced by multiple factors such as mineral evolution,hydrocarbon generation,and cracking and conversion of crude oil,the Gulong shale exhibits varying pore-fissure combinations at different evolutionary stages.At the mature stage,the shale predominantly contains micron-scale dissolved pores and organo-clay complex pores/fissures(i.e.,pores/fissures with clay minerals as framework and formed as a result of hydrocarbon generation).In contrast,the highly mature stage is characterized by nano-scale organo-clay-complex pores/fissures and bedding fissures;(3)There exists a coupling relationship between the shale oil enrichment and the evolution of pore-fissure combinations for the Gulong shale.The shale oil primarily accumulates within inorganic intergranular and intercrystalline pores at the low mature stage,while it is relatively heavy and predominantly concentrates in dissolved pores and organo-clay complex pores/fissures at the mature stage.At the highly mature stage,the shale oil becomes lighter and largely gets enriched in organo-clay complex pores/fissures and bedding fissures.
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万方数据
维普
