Reservoir Characteristics And Oil Enrichment Rule Of Shale Series In The First Member Of Qingshankou Formation In Gulong Sag

In Gulong sag,Qingshankou group mud shale is an important hydrocarbon source rocks in the Daqing oilfield.In recent years,some drilling to Qingshankou wells had good oil and gas shows,was an important layer system to increase production in Daqing oil field.In order to determine the reservoir characteristics of shale formations,in this study,we applied the rock thin section,scanning electron microscope,X-ray diffraction,nitrogen adsorption,high pressure mercury,CT and confocal laser scanning techniques,for fine classification of lithofacies,and the characteristics of mineral content,reservoir property,diagenesis,pore structure,oiliness and brittle plasticity were revealed.The results show that the porosity of Shale Series in the first member of Qingshankou formation in Gulong Sag was 5%-15%,and the permeability is mainly below 0.01×10-3um2,which is characterized by low porosity and low permeability.On the whole,the shale in this area was in the middle digenetic A2-B sub period,and the pore type was mainly intergranular pore,because of the organic matter type and the low degree of thermal evolution of organic matter,the organic pores were less developed.According to the abundance of organic matter in rock,sedimentary structure,mineral composition of the three standards,the reservoir rock facie was divided into seven categories:?high organic lamellae clayey mudstone,?high organic massive felsic mudstone,?medium organic massive felsic mudstone,?medium organic laminal felsic mudstone,?low organic laminal felsic mudstone,?low organic siltstone interlayer,?low organic mussel-shrimp limestone interlayer.The organic carbon content of laminal felsic mudstone was about 1.3% on average,the pore throat type dominated by open parallel wall slit holes and open wedge holes,the pore length of the capillary pressure curve is longer,the sorting is better,the mesopores and the macro holes are well developed.The pore form is mainly in the form of microtubules,which are distributed along the bedding plane and connected with each other to form the pore-throat network system,has good oiliness and high brittleness and anisotropy.Therefore,it is considered that the laminal felsic mudstone,medium organic laminal felsic mudstone,is the most favorable reservoir facies in this study area.The laminal felsic mudstone in the first Member of Qingshankou formation developed many layers,the dark layer had a great potential for hydrocarbon generation,and the development of the reservoir space of the light colored layer provided the basis for the formation and retention of oil and gas.In addition,the thickness of the source rock in the study area is large,the permeability is low,resulting in the increase of the fluid starting resistance,the oil and gas do not have the condition of large-scale outward discharge and remain in the source rock layer,thus formed an overpressure,but the formation pressure caused by hydrocarbon generation is not enough to break through the resistance of oil and gas migration,and the oil is trapped in the larger pores of the lamellar mudstone to form mudstone matrix shale oil.