Modeling of hydrocarbon adsorption on continental oil shale: A case study on n-alkane

Oil adsorption on the pore surface of tight shale affects the transport and even recovery of oil through shale reservoir. In this paper, an innovative model evaluating the n-alkane adsorption on shale was developed theoretically according to the hydrocarbon vapor adsorption (HVA) process and was verified by the n-decane (i.e., n-C10) adsorption on continental oil shale obtained from the Dongying sag of the southeastern Bohai Bay basin of China. The model considered the multilayer adsorption of hydrocarbon and the microscopic characteristics of the shale pore system. For a case study, several parameters in the models were determined by low temperature nitrogen adsorption/desorption (LT-N2A/D) and HVA tests combined with recently reported molecular dynamics simulation. Next, optimal values of the coefficients k and β were determined by fitting the experimental data with the model and were used to calculate the n-C10 adsorbed amount under 0.8 P/P0 and 298.15 K condition. Simultaneously, the n-C10 condensed (i.e., free-phase-like) amount was obtained. The primary results demonstrate that (1) n-C10 adsorbed amount is obviously lower than condensed amount and varies from 0.097 to 0.619 mg/g (mean 0.311 mg/g), accounting for 1.68-3.76% (mean 2.32%) of the total amount. (2) Both the adsorbed and condensed amounts are directly controlled by total pore volume, which are mainly contributed by organic matters and secondarily by pyrite and siderite in shale. The model will be potential useful to evaluate the shale oil adsorption.