Factors Influencing Enrichment And Mobility Of Continental Shale Oil In Biyang Sag

With the depletion of conventional oil and gas resources,unconventional oil and gas resources have attracted more and more attention.Shale oil,as an important member of unconventional oil and gas resources,has great exploration and development potential.Its potential resources are far more than the conventional oil and gas resources found at present,and play a decisive role in the future development of energy industry.Shale oil resources in China are abundant,but due to geographical constraints resulting in uneven distribution of resources and poor mobility of continental shale,the exploration and development process of shale oil in China is slow.Therefore,the analysis of the main factors controlling the enrichment and mobility of continental shale oil is of great significance to the efficient development of shale oil in China.Taking Biyang Sag as an example,this paper selected core samples from key wells for TOC analysis,X-ray diffraction,scanning electron microscopy,nuclear magnetic resonance,low-temperature nitrogen adsorption,high pressure mercury intrusion test,etc.On the basis of a large number of experimental data,this paper evaluates the factors influencing enrichment and mobility of continental shale oil in Biyang Sag from five aspects including hydrocarbon generation basis,reservoir space,mineral composition,crude oil composition and crude oil adsorption characteristics of shale oil.And this research divides and predicts the favorable depth and well location of oil-bearing property and mobility.(1)Oil-bearing property of shale is the basis of shale oil mobility.Geochemical studies show that the organic matter types of source rocks with good oil-bearing properties in the study area are mostly type I and type II.The TOC content is more than 2%,and the saturated hydrocarbon content is more than 50%.Because the non-polar molecule with lower viscosity has better mobility,the oil content of shale has a positive correlation with mobility.(2)Shale oil mainly exists in inorganic macropore with weak heterogeneity.Because both helium measurement and high pressure mercury injection can reveal the development of macropore,while low temperature nitrogen adsorption experiments mainly reveal the development of micropore and mesopore,helium porosity and mercury injection specific pore volume are positively correlated with the oil content of shale.The specific pore volume of nitrogen adsorption at low temperature is negatively correlated with oil content of shale,which proves that shale oil mainly exists in macropore.SEM observation shows that shale pore is mainly composed of intergranular pore,dissolution pore and other inorganic pore,while organic pore is not developed.At the same time,the negative correlation between the specific surface area of shale and the abundance of organic matter further proves this point.Fractal dimension study shows that the homogeneity of macropore is good and the pore structure is relatively simple,so the oil-bearing property of shale is good.(3)When the content of clay minerals and feldspar in shale is higher,the organic matter abundance is lower and the oil content is worse.When the quartz content is high,the organic matter abundance is high and the oil content is good.Low temperature nitrogen adsorption experiments and crude oil adsorption and desorption experiments show that clay minerals have more micropore and mesoporous,and are the main carriers of crude oil adsorption.Clay minerals have strong adsorbability to crude oil,and more clay minerals will make their mobility worse.(4)Through hydrocarbon expulsion threshold method,the mobile index of shale oil in the study area is determined as S₁/TOC×100=60mg HC/g TOC,and chloroform asphalt"A"/TOC=0.2.According to mobility index,the favorable interval for enrichment and mobility in Biyang Sag is 3000m.On the basis of light hydrocarbon and heavy hydrocarbon recovery correction of S₁,the oil-bearing and movability of key shale series in the study area were evaluated.The recoverable movable oil resource of 5th shale formation of Third Member of the Hetaoyuan Formation is 1.01×10⁸t.The recoverable movable oil resource of 6th shale formation of Third Member of the Hetaoyuan Formation is 0.22×10⁸t.These areas are the main targets for drilling and deployment in Biyang Sag in the future.