Light Alkane Competition for Pore Space in Unconventional Petroleum Reservoirs at Intermediate Thermal Maturities

Petroleum from unconventional reservoirs continues to be an important component of the U.S. energy endowment and is predicted to remain so in the near future. However, there is limited understanding of the fine (<25 nm diameter) pore networks that exists in these geologic formations and how fluids behave in such pore networks under reservoir conditions, especially for formations producing natural gas plant liquids (i.e., methane, ethane, propane, butane, isobutane, and pentane). This lack of knowledge adds to uncertainty for estimated ultimate recovery of resources from unconventional reservoirs. To address knowledge gaps associated with the pore size distribution and behaviour of petroleum components in unconventional reservoirs we propose to use the NIMROD to determine if methane and ethane will segregate from a 50%-50% mixture into different pore sizes in a sample from the Niobrara Formation, an active unconventional petroleum play. We hypothesize that methane will be preferentially segregated into smaller pores in the Niobrara Formation sample. If this is the case, it suggests that when assessing unconventional petroleum reservoirs for natural gas plant liquids an understanding of fine porosity will be less important than when assessing these reservoirs only for methane.