Fine-grained rock fabric facies classification and its control on shale oil accumulation: a case study from the Paleogene Kong 2 Member, Bohai Bay Basin

Lacustrine shale oil resources in China are abundant,with remarkable exploration breakthroughs being achieved.Compared to marine shale oil in North America,efficient exploration of lacustrine shale oil is more difficult;thus,selecting favorable layer and optimization zone for horizontal wells is more important.In this study,based on systematic coring of approximately 500 m fine-grained deposits of the Kong 2 Member,combining laboratory tests and log data,source rock geochemistry and reservoir physical properties,the favorable rock fabric facies for oil accumulation was analyzed and classified.First,the dominant lithologic facies,organic facies,and bed combination facies were determined based on mineral composition from logging,total organic content(TOC),and sedimentary structure.Secondly,10 fabric facies were classified by combining these three facies,with 4 fabric facies were found to have high TOC content,high total hydrocarbon,and strong fluorescence features,indicating good shale oil enrichment.Thirdly,the distribution of the upon good fabric facies was identified to be located at the top of the Kong 2 Member,with evidences of seismic resistivity inversion,thermal maturity,structure depth,and strata thickness.And the favorable facies were found to be stably distributed lateral at the area of about 100 km2.High oil flow has been detected at this layer within this area by several wells,including horizontal wells.The exploratory study of fabric facies classification and evaluation provides a new research idea for lacustrine shale oil exploration and effectively promotes breakthroughs in lacustrine shale oil exploration in Bohai Bay Basin.

The rudist buildup depositional model,reservoir architecture and development strategy of the cretaceous Sarvak formation of Southwest Iran

This paper studies the lithofacies,sedimentary facies,depositional models and reservoir architecture of the rudist-bearing Sar-3 zone of Cretaceous Sarvak in the Southwest of Iran by utilizing coring,thin section,XRD data of five coring wells and 3D seismic data.Research results include the following:According to lithofacies features and their association,the rudist-mound and tidal flat are the main microfacies in the Sar-3 depositional time.By investigating the regional tectonic setting and seismic interpretation,a depositional model was built for the Sar-3 zone,which highlights four key points:1)The distribution of the rudist-buildup is controlled by the paleo-high.2)The build-up outside of the wide colonize stage but reached the wave-base level in a short time by regression and formation uplift,and was destroyed by the high energy current,then forming the moundy allochthonous deposition after being dispersed and redeposited.3)The tidal flat develops widely in the upper Sar-3,and the deposition thickness depends on the paleo-structure.The tidal channel develops in the valley and fringe of the Paleo-structure.4)The exposure within the leaching effect by the meteoric water of the top of Sar-3 is the main controlling factor of the reservoir vertical architecture.The Sar-3 zone featured as the dualistic architecture consists of two regions:the lower is the rudist reef limestone reservoir and the upper is the tidal condense limestone interlayer.The thickness of each is controlled by the paleo-structure.The Paleo-high zone is the preferential development zone.Based on reservoir characteristics of the different zones,a targeted development strategy has been proposed.Keeping the trajectory in the middle of the oillayer in the paleo-high,and in the paleo-low,make the trajectory crossing the oil-zone and then keep it in the lower.