Semi-analytical evaluation for water-alternating-CO 2 injectivity in tight oil reservoirs

This paper presents a new semi-analytical model to estimate the bottom-hole pressure drop for a water-alternating-CO2 injection well in a horizontal, linear, homogenous tight oil reservoir with constant-pressure boundary. In this model, the conventional Buckley-Leverett (B-L) equations are modified to consider the interaction between CO2 and oil or water. The Laplace transformations and Stehfest inversion algorithm are employed to solve the model. Through the comparison of pressure profile between proposed and numerical models at different times, and the match of pressure drop with experiments and numerical simulation data collected from published paper, the model accuracy is validated. The sensitivity analysis indicates that with the reduction of CO2-oil interfacial tension and the increase of CO2 slug size, the water injectivity will be improved. The water injectivity strongly depends on the reservoir permeability. When the formation permeability is lower than 0.075 mD, the injectivity will decline drastically. [Received: December 12, 2017; Accepted: June 6, 2018]