Development of a Trilinear Flow Model for Carbon Sequestration in Depleted Shale

Abstract

Abstract While many researchers are trending to seek the conventional geological sequestrations for CO2 storage, like saline aquifers, depleted conventional hydrocarbon reservoirs, and unminable coal seams, only a few are interested in depleted shales for safety and economic reasons. Thus, for reservoir engineers, lots of work needs to be done to better this situation. First and foremost, it is an urgent issue should be settled how to estimate the CO2 storage capacity in depleted shale. In this paper, a new analytical method to estimate CO2 storage in shale wasdeveloped. First, a trilinear flow model was proposed for the injection well, namely a multiple fractured vertical well (MFHW), at a constant injection rate. The model incorporated with multiple mechanisms including Knudson diffusion, gas adsorption, and effect of stress-sensitivity. Then, the transient pressure solution of injection well is solved by applying mathematical methods. Subsequently, CO2 storage capacity was evaluated according to the transient pressure performance of injection well. After that, model verification as well as sensitivity analysis was conducted. Finally, we applied the proposed method into a case derived from the New Albany Shale, which has been proved to be a promising candidate for CO2 storage. The results show that a good agreement exists between our analytical results and these numerical solutions. The average difference is about 2.57%, which shows our methodology is reasonable. Further, it only takes about 10s CPU times with 100 time step by employing the proposed approach to estimate the CO2 storage capacity of the study area in the New Albany Shale, which indicates the new approach is rapid. Additionally, results of sensitive analysis show that as stress-sensitivity coefficient, adsorption index, and Knudsen diffusion coefficient increase, CO2 storage capacity increases. As storage ratio increases, CO2 storage capacity decreases. This meaningful work provides a new angle on estimation of CO2 storage capacity, which is beneficial to exploit the residual depleted shale reservoirs as well as cut CO2 emission.