Shale Oil Accumulation Rules And Favorable Areas Selection Of Es₄² Member In Damintun Depression

As the famous“small and rich”Cenozoic continental sag in the east part of China,shale oil of Es₄² member in Damintun depression has great exploration potential.From top to bottom,this member contain upper part,middle part and lower part,and has the obvious"sandwich"structure.According to the characters of element geochemistry and biomarker compounds to analyze sedimentary environment of Es₄² member,the results show that this member formed in reducing sedimentary environment,the water salinity mainly is fresh-brackish and fresh water,the ancient climate is dry heat and wet climate,and the origin of organic matter is mainly mixed source.The hydrocarbon source rocks of Es₄² member with high abundance of organic matter,In particular,the upper part has the highest abundance,the lower part,secondly,and the middle part is the worst.The organic matter type is good,mainly type I and II₁,and organic matter maturity is low-mature and mature stage.According to the delta LogR model to evaluate organic heterogeneity of shale oil,using the method of extraction,pyrolysis and the theory of hydrocarbon generation kinetics to restore the light and heavy hydrocarbon of pyrolysis parameters S₁,and predict the shale oil resources based on volume method,the results show that the shale oil resources of Es₄² member in Damintun depression is 3.11x10⁸ t,the planar distribution has three high value area,main enrichment in shen 352 well,shen 224 well and shen 309 well-sheng 14 well.For vertical distribution,the shale oil resources of upper part is1.95x10⁸ t,the lower part is 0.95x10⁸ t and middle part is 0.21x10⁸ t.At the same time,according to nuclear magnetic resonance（NMR）T₁-T₂ technology and shale saturation-centrifugal experiment to determine to lower limit of movable oil,the results is S₁>TOC/1.1803-1.1803,and calculate the movable resources of Es₄² member shale oil is1.04x10⁸ t,specially,the movable resource of upper part is 0.39x10⁸ t,the middle part is0.14x10⁸ t,and the lower part is 0.51x10⁸ t.Based on the results of core physical property test,the porosity are mainly distributed between 2⁶%and permeability are mainly distributed between 0.001⁰.5 mD,the reservoir space of Es₄² member is microfracture,dissolution pore,intergranular pore,in particular,the lower part reservoir has more dissolution pore and micro crack while the upper part reservoir has more microporous.According to the characterization of complete pore size distribution using nuclear magnetic resonance（NMR）,the lower part of the reservoir has the larger pore size distribution,the main peak at 80 nm,while the upper and middle part is smaller.According to relationship between the movable fluids content tested by nuclear magnetic resonance（NMR）and shale physical properties to establish the standard of high quality reservoirs:porosity is greater than 6%,permeability is greater than 0.1 mD.Using neural network and gross volume model to calculate the brittle mineral content,using conventional well logging to extract shear wave and calculate the rock mechanics parameters of the shale reservoir.A comprehensive characterization of shale reservoir fracturing can be evaluated based on the brittle mineral content and young’s modulus,the advantageous area for the shale fracture has high brittleness mineral content and low young’s modulus.According to fracturing evaluation model to predict the reservoir fracturability of Es₄² member,the results show that the lower part reservoir fracturability is highest,the second is upper part,and the middle part is the worst.For the planar distribution,the fracturability index great than 0.7 mainly near in shen 352 well and shen 224 well.According to the plane distribution and vertical changes of shale oil resource intensity,sedimentary environment,geochemical characteristics and reservoir features to explore shale oil enrichment regularity.Es₄² member formed in a relatively occlusion of reducing sedimentary environment,the west and east of depression has thick mudstone,oil shale and cloud,the thickness up to 200 m.Sedimentary environment decided the scale of source rocks,the higher scale of source rocks,the greater the resource is relatively higher;Es₄² member of source rocks with high abundance of organic matter,good types and moderate maturity,provide sufficient hydrocarbon sources for shale oil accumulation,the higher organic matter abundance,the shale oil resources more enrichment;organic matter thermal degradation generates a large amount of organic acids in the process of burial,the dissolved minerals can form a large number of secondary pores,which provide a good reservoir space for the enrichment of shale oil in the member of Es₄².In this paper,the standard of favorable areas selection is:porosity is greater than 6%,movable oil content is more than 40 x 10⁴ t/km²,fracturability index is greater than 0.7.In general,the shale oil resources in favorable areas is 0.61x10⁸ t,movable resource is 0.29x10⁸t.Specially,the lower part is the best,the upper part is second,and middle part has no favorable area because of resource is small.In the lower part,there are three favorable areas,enrichment in shen 352 well,shen 224 well and shen 309 well,respectively.The shale oil resources in favorable areas at lower part is 0.46x10⁸ t,movable resource is 0.24x10⁸ t.In the upper part,the favorable area just near shen 352 well and shale oil resources is 0.15x10⁸ t,movable resource is 0.05x10⁸ t.