Imbibition Characteristics and Model for Ultra-low Permeability Reservoir

Abstract

AbstractUltra-low permeability reservoir has low permeability and developed micro fractures. Conventional water injection is difficult to supple formation energy. Imbibition is the key technology for the development of ultra-low permeability reservoir. In order to accurately characterize the imbibition process of ultra-low permeability reservoir, based on the two-phase flow theory, the mathematical model of imbibition and the analytical solution of recovery and self-priming time are derived with the consideration of parameters such as gravity, initial water saturation and capillary force. Based on the theoretical analysis of fluid self-priming flow mechanics, a dimensionless time model considering multiple factors is derived. On the basis of laboratory imbibition experiment and nuclear magnetic resonance technology, the imbibition recovery of ultra-low permeability core and the distribution of oil and water in the process of imbibition are obtained. The results show that the imbibition recovery of hydrophilic core in ultra-low permeability reservoir can reach 22%–28%, the imbibition effect is obvious, and the crude oil in small pores is mainly developed, and the recovery in small pores can reach about 35%, and the imbibition time is long. The dimensionless imbibition time and normalized recovery are calculated by using the derived imbibition model, and the results can be well fitted. The calculation results can be used to make the imbibition chart of ultra-low permeability reservoir, it is very important for the design of water injection scheme and the prediction of imbibition recovery in ultra-low permeability reservoir.KeywordsUltra-low permeability reservoirImbibition recoveryDimensionless timeImbibition modelImbibition experiment