Abstract
In shale, liquid hydrocarbons are accumulated mainly in nanometer-scale pores or fractures, so the pore types and PSDs (pore size distributions) play a major role in the shale oil occurrence (free or absorbed state), amount of oil, and flow features. The pore types and PSDs of marine shale have been well studied; however, research on lacustrine shale is rare, especially for shale in the oil generation window, although lacustrine shale is deposited widely around the world. To investigate the relationship between nanometer-scale pores and oil occurrence in the lacustrine shale, 10 lacustrine shale core samples from Songliao Basin, NE China were analyzed. Analyses of these samples included geochemical measurements, SEM (scanning electron microscope) observations, low pressure CO2 and N2 adsorption, and high-pressure mercury injection experiments. Analysis results indicate that: (1) Pore types in the lacustrine shale include inter-matrix pores, intergranular pores, organic matter pores, and dissolution pores, and these pores are dominated by mesopores and micropores; (2) There is no apparent correlation between pore volumes and clay content, however, a weak negative correlation is present between total pore volume and carbonate content; (3) Pores in lacustrine shale are well developed when the organic matter maturity (Ro) is >1.0% and the pore volume is positively correlated with the TOC (total organic carbon) content. The statistical results suggest that oil in lacustrine shale mainly occurs in pores with diameters larger than 40 nm. However, more research is needed to determine whether this minimum pore diameter for oil occurrence in lacustrine shale is widely applicable.
Highlights
The growing demand for energy has resulted in continuously increasing consumption of conventional oil and gas resources and has driven a new wave of exploration for oil and gas
Free oil or volatile hydrocarbon content, expressed as mg HC/g rock (S1), the residual hydrocarbon generation potential, expressed as mg HC/g rock (S2), the temperature of maximum pyrolysis yield (Tmax), and the quantity of pyrolyzate, expressed as mg HC/g rock generated from kerogen during gradual heating in a helium stream are normalized to TOC to give the hydrogen index (HI; mg HC/g TOC)
The geochemical experimental results show that the samples have high TOC contents, with a minimum TOC content of 1.73 wt.%, a maximum of 4.21 wt.%, and an average of 2.72 wt.%
Summary
The growing demand for energy has resulted in continuously increasing consumption of conventional oil and gas resources and has driven a new wave of exploration for oil and gas. In addition to exploration for conventional petroleum, unconventional oil and gas are attracting more attention. The ‘shale gas revolution’ in North America has triggered a worldwide upsurge in shale gas exploration. An emphasis has been placed on shale oil exploration and development, stimulated by decreases in natural gas prices.
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