Effect of occurrence states of fluid and pore structures on shale oil movability

Abstract

The occurrence states of oil in the kerogen and structural characteristics of shale are unfavorable for the production of shale oil. Understanding the movability of oil and water at different occurrence states or in different pore structures is important for the development of shale oil reservoirs. Therefore, a high-speed centrifugation experiment based on the nuclear magnetic resonance technique was conducted for shale samples saturated with oil and water to test the movability of oil and water in the shale. To describe the effect of nanopores and the direction of capillaries on the movability of oil and water in the shale, a mathematical model based on the variational diameter capillary model was developed. The results indicated that a larger amount of bound oil (the adsorption-dissolution oil in the kerogen and the oil in the nanopores) was present in the shale, which is 3.12–5.44 times the amount of bound water (the adsorption oil on the interlayer of clay and the oil in the nanopores). The movability of free water (up to 88.8%) in the shale was larger than that of free oil (up to 68.1%) and the movability of free fluid (up to 88.8%) in the shale was significantly larger than that of bound fluid (up to 12.4%). According to the model, most of the capillary diameters of the shale gradually increased in the direction of the centrifugal force and weakened as the lamination developed. The movability of bound oil and water in the nanopores was larger than the theoretical value.