Characteristics And Resource Potential Of Oil Shale In The Lower Cretaceous Jiufotang Formation In Beipiao Basin

Beipiao Basin is located in the western part of Liaoning Province,where oil shale resources are huge.Oil shale is mainly distributed in the lower Cretaceous Jiufotang Formation.By using the theories and methods of sedimentology,sequence stratigraphy and geochemistry,the oil shale series in Beipiao Basin are systematically studied,thus revealing the characteristics of oil shale and the distribution law and resource potential of oil shale in the study area,providing a scientific basis for further guiding the exploration and development of oil shale.There are nine layers of oil shale in Jiufotang Formation in the study area.The oil shale is dark grey and grey black with well-developed shale and common horizontal bedding.The oil content of the oil shale in the second-1 reservoir is the highest,with the average oil content of5.10%and the highest oil content of 6.36%.It belongs to oil shale with high ash content,medium-high calorific value,low sulfur content and medium oil content.The kerogen type of medium and high quality oil shale is type I,and that of low quality oil shale is type I-II ₁,which is in the stage of immature and low maturity.The Jiufotang Formation in the study area mainly develops the lacustrine facies,further dividing the shallow lake and the deep lake-semi-deep lake subfacies.Combined with the field outcrops and drilling data,the target layer has identified a three-level sequence,mainly developing the water inlet system.Domain?TST?and High Water System Domain?HST?.The water inlet system is a dewatering superposition method,mainly for shallow lakes and deep lake-semi-deep lake sediments.The deep lake-semi-deep lakes are gradually increasing toward the center of the basin,and the organic matter begins to enrich and develop well-developed oil sheets.Rock;high water level system domain,mainly for accretion type superposition,deep lake-semi-deep lake sedimentation is widely developed,organic matter is the most abundant,oil shale has higher oil content and greater thickness.The total thickness of oil shale of Jiufotang Formation in the study area is 143.15m.The thickness and distribution scale of oil shale is the largest in the third layer and the second layer.Oil shale develops in the whole study area,but in the central and northeastern part,the thickness of oil shale is the largest and the oil-bearing rate is higher,while in the western part,the thickness of oil shale is smaller and the oil-bearing rate is lower.This paper evaluates the resources of Daqingshan,Naiman Banner,Taijiying-Nantaizi ore-bearing areas and prediction areas by volume method.The results of resource evaluation show that the oil shale resources in Beipiao Basin are 140025 thousand tons,and the converted oil shale resources are 7238 thousand tons.Among them,the oil shale resources in Daqingshan ore-bearing area are 93202 thousand tons and the converted oil shale resources are 4785 thousand tons;and the oil resources in Naimanqi ore-bearing area are 4785 thousand tons.Shale resources are 15534thousand tons,converted into 859 thousand tons of synthetic oil shale oil resources;oil shale resources are 3043 thousand tons in Nantaizi mining area,converted into synthetic oil shale oil resources are 144 thousand tons;oil shale resources are 28246 thousand tons in Beipiao basin prediction area,converted into synthetic oil shale oil resources are 1450 thousand tons.