Study on the Technology of Imbibition in Ultra-low Permeability Reservoir

In the development process of ultra-low permeability reservoir, due to the dual heterogeneity of matrix and fracture, it is difficult to establish effective pressure system, and water flooding occurs along the fracture. Based on the analysis of the fractured ultra-low permeability reservoir production mechanism, the imbibition characteristics and the main influencing factors of the fractured ultra-low permeability reservoir are studied by means of laboratory imbibition experiment and nuclear magnetic resonance technology (NMR). The results show that the imbibition of hydrophilic core mainly occurs in the early stage of imbibition, and there are optimal imbibition time and optimal water injection times in the imbibition process. The first soaking process has the most obvious imbibition effect; the imbibition effect mainly displaces the crude oil in the small channel and the wall of the large channel, and the displacement effect mainly acts on the crude oil in the large channel. Through the nuclear magnetic resonance technology, the displacement and imbibition effect can be calculated quantitatively; for ultra-low permeability reservoir, the reasonable injection speed suitable for imbibition and displacement is between 0.03–0.1 ml/min. The main influencing factors of imbibition include wettability, permeability, injection rate, engineering factors and working system. According to the characteristics of ultra-low permeability reservoir, the development mode of “volume fracturing + imbibition” is put forward. Applying the research results to KB oilfield, the recovery degree is predicted to be 4.1% higher than the original development plan after 7 years. The research content has guiding significance for the development of hydrophilic fractured ultra-low permeability reservoir.