Experimental Verification of Changing Bubble Points of Oils in Shales: Effect of Preferential Absorption by Kerogen and Confinement of Fluids

Abstract

Abstract The economic and increased production of oil and gas from shale plays in the United States plays a key role in the country's energy independence. There are many factors that govern increased production of oil and gas from shales. One such factor is the assessment of the correct in-situ oil bubble point in shales which is critical in the optimization of hydrocarbon production. Shales are nano porous organic-rich sedimentary rocks that act as both source and reservoir oil and gas systems. The effect of nano pore confinement on the bubble point of oil in shales has been widely studied and documented in the SPE papers. However, the effect of organic matter presence on the bubble point of oil in shales has not been explored. The researchers at the University of Utah has studied both the effects by performing molecular scale simulations, thermodynamic modeling and experiments using analytical tools. This paper discusses the experimental effect of the presence of nano pores and organic matter on the bubble points of oil in shales. Experiments are performed on isolated type I kerogen with multiple pure component hydrocarbons and crude oil. Differential Scanning Calorimeter (DSC) was used to perform experiments on mixture of kerogen and hydrocarbons. The DSC data shows that the presence of kerogen and presence of nano pores changes the bubble point temperature. There is a suppression in the bubble point temperature of oil in presence of type I kerogen. This suppression is larger in the boiling point temperatures of pure polar and non-polar components (nitrobenzene, heptane) when in presence of kerogen. The paper discusses the possible reasons for the suppression seen due to the two effects and the reason behind the difference in the suppression seen with changing hydrocarbon liquid (polar vs non-polar vs H-bonding). Any multicomponent mixture of hydrocarbons such as oil will be split into an absorbed (in kerogen) phase and a free phase as a result of preferential absorption of preferred components by kerogen. Changes in the composition of oil in kerogen due to such a phase split will change the bubble point of oil in kerogen. This is known as effect of presence of kerogen. The free phase stays under the confinement in the nano poresof kerogen. The bubble points of confined oils are different than the bubble point of bulk oil due to dominant pore-wall and fluid interaction under nano-confinement.