Abstract
Shale oil is a vital alternative energy source for oil and gas and has recently received an extensive attention. Characterization of the shale oil content provides an important guiding significance for resource potential evaluation, sweet spot prediction, and development of shale oil. In this paper, the mechanism, evaluation and influencing factors of oil retention in shales are reviewed. Oil is retained in shales through adsorption and swelling of kerogen, adsorption onto minerals and storage in shale pores. Quite a few methods are developed for oil content evaluation, such as three-dimensional fluorescence quantitation, two-dimensional nuclear magnetic resonance (2D NMR), solvent extraction, pyrolysis, multiple extraction-multiple pyrolysis-multiple chromatography, logging calculation, statistical regression, pyrolysis simulation experiment, and mass balance calculation. However, the limitations of these methods represent a challenge in practical applications. On this basis, the influencing factors of the oil retention are summarized from the microscale to the macroscale. The oil retention capacity is comprehensively controlled by organic matter abundance, type and maturity, mineral composition and diagenesis, oil storage space, shale thickness, and preservation conditions. Finally, oil mobility evaluation methods are introduced, mainly including the multitemperature pyrolysis, 2D NMR, and adsorption-swelling experiment, and the influencing factors of movable shale oil are briefly discussed. The aim of this paper is to deepen the understanding of shale oil evaluation and provide a basis for further research.
Highlights
Compared to conventional petroleum systems, shale strata exhibit the characteristics of low porosity and ultralow permeability, and shale oil and gas have received insufficient attention for a long time due to the great difficulty of exploitation (Jarvie, 2012; Chen L. et al, 2019b; Soeder and Borglum, 2019)
The three methods of the pyrolysis, thermal simulation experiment and material balance will be futher presented, which are commonly adopted to evaluate the shale oil conten based on geochemical data
The movable oil content in shales is the key to a high yield of shale oil
Summary
Compared to conventional petroleum systems, shale strata exhibit the characteristics of low porosity and ultralow permeability, and shale oil and gas have received insufficient attention for a long time due to the great difficulty of exploitation (Jarvie, 2012; Chen L. et al, 2019b; Soeder and Borglum, 2019). In 2019, the proven reserves in key shale oil exploration areas in the United States reached 232.40 × 108 bbl, shale oil production yielded 22.78 × 108 bbl (US Energy Information Administration, 2021), and shale oil exploitation is. Argentina, Canada and other countries possess a colossal shale oil resource potential, with recoverable shale oil resources of 746 × 108 bbl, 270 × 108 bbl, and 88 × 108 bbl, respectively (US Energy Information Administration, 2015). The daily output of shale oil in Canada and Argentina is approximately 40 × 104 bbl/d and 5 × 104 bbl/d, respectively (Yang and Jin, 2019), the shale oil contained in the Mesozoic Bazhenov-Abalak Formations has been experimentally exploited in Russia, and the average horizontal well production reached 55.13 bbl/d in 2016 (Liang et al, 2019)
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