Discussion on Movability of Shale Oils in the Paleogene of Dongying Depression

J, et al, 2007, Lucas W B, 2010), is widely developed in lacstrine basins of East-China (Li Juyuan, et al, 2014). Having representative geology characters of lactrine basins, the Dongying Depression’s formation and evolution history provides favorable organic material and geological conditions for shale oil generation and preservation. Therefore, the commercial oil flows are found in shale formations occasionally. However, the majority of the shale oil resource cannot be effectively explored and exploited up to nowadays, because of the low permeabilities of shale reservoirs and unconsciousness about controlling factor acting on oil’s flow ability. In this paper, some geology parameters of shale and hydrocarbon fluid, which probably affects shale oil move ability, and their evolution rules were discussed, which include hydrocarbon fluid property (oil contents of shale, oil phase and oil viscosity in situ), clay component of shale, formation fluid pressure. Because the light components (C14-) are important parts of shale oils but can not be analyzed easily, while the data of the chloroform bitumen “A” (C14+) of shales in the Paleogene of Dongying Depression are abundant, the oil content of shale was calculated with chloroform bitumen “A” and the relationship between C5-C14 amounts and chloroform bitumen “A” (C15+) amounts in shale samples of different evolution stages (Zhang Linye, et al, 2014), therefore, the oil saturation of shale was obtained with oil content and shale porosity. The oil saturations of shales of the Es3 and the Es4 (Fig.1), varying widely from 1% to 80%, rise up to maximum value then go down with burial depth’s increasing. The maximum values of oil saturations match well with hydrocarbon generation peaks of shale. The component and phase type of oil fluids in shale of the Paleogene in Dongying Depression were studied with high pressure and high temperature oil generation simulation experiments. The immature shale smples of the Paleogene were heated to various temperatures and exerted to various pressures to simulate the courses of shale evolution and oil generation. The Ro% of samples after simulation was measured to match the simulation temperature with the evolution burial depth according to the relationship between Ro and burial depth of factual sample. In addition the oil and gas produced in the simulation experiment were colleted and analyzed, and then, according to oil and gas components, the P-T phase diagrams of oils and gases generated in experiment were calculated and plotted. Therefore, the oil/gas phase types in different burial depths were ascertained in line with the P-T diagrams of hydrocarbon fluid and formation temperature and formation pressure. The oil phase type of oil in shales of the Es4 menmber of the Paleogene can be summarized: the majority of the hydrocarbons in shales shallower than 4200m are in state of black oil phase with all the natural gases dissolved in oil, and minority of viscous oils existed in shales between 2800 m ~ 2900 m; the hydrocarbons in shales are convert to condensate gas at the depth of about 4300 m, with light oils dissolved in gases; the burial depths from 4200 m to 4300 m are transition zone where oil phase and condensate phase coexist (Fig.1). Because all the shales of the Es3 are buried shallower than 4000 m, all the hydrocarbons in shales of the Es3 are in state of black oil. With natural gases dissolved in oils. The formation hydrocarbon fluid viscosities of shale oil cannot be measured, but can be derived from PVT experiment viscosity data of oils in inner-source reservoirs, which include shale fracture reservoir and conventional reservoir, because the components and viscosity of oil in inner-source reservoir is similar to that in surround shale. The oil viscosities of shale oils decline obviously with the burial depth increasing, varying from 20 mPa.s in 2500 m to 0.5 mPa.s in 3800 m. Moreover, the viscosities of shale oils between 3000 to 3500 m go down with burial depths increasing more dramatically than any other burial depth. The viscosities of oil are affected by temperature and component of oil, while the BAO Youshu, LI Zheng, LI Juyuan, WANG Yurong, WU Lianbo, ZHANG Lei and ZHU Rifang, 2015. Discussion on Movability of Shale Oils in the Paleogene of Dongying Depression. Acta Geologica Sinica (English Edition), 89(supp.): 372-374.