In-Situ Generation and Propagation of a Nanocellulose Reinforced CO2 Foam in Tight Formation Fractures for Conformance Control

Abstract EOR projects implemented in Bakken and Changqing tight formations demonstrated that the fractures could cause early breakthrough of the injected CO2 and finally led to undesirable oil recovery. Therefore, conformance control technologies should be developed for the outstanding EOR performance in fractured tight formations. Given this, a nanocellulose (NCF) reinforced CO2 foam was rationally designed in the present work and the flow behaviors in tight formation fractures including generation, propagation and permeability reduction were investigated. The bulk properties of NCF-CO2 foam in gas and supercritical states including foam stability and texture were thoroughly evaluated in a high-pressure-high-temperature (HP-HT) windowed cell. A series of model fractures with certain apertures in tight rocks were designed and assembled for coreflooding experiments. The differential pressure (ΔP) across the core sample during foam flow was continuously monitored. At the end of the experiments, the produced ΔP as a function of gas and water injection rate was mapped. The results showed that the addition of NCF into CO2 foam considerably retarded foam film drainage and bubble coalescence thereby improving the stability of the induced foam. The NCF-CO2 foam had finer bubbles and more robust lamella film than conventional CO2 foam. As a consequence, the half-life of NCF-scCO2 (supercritical state) foam was found to be two times longer than the counterpart conventional scCO2 foam. It was also observed that NCF-CO2 foam could rapidly generate in-situ in fractures and propagate throughout the models. Small fractured aperture led to high ΔP under identical experimental conditions. In addition, NCF-scCO2 foam exhibited noticeably higher ΔP compared to conventional scCO2 and NCF-CO2 foams, validating the effectiveness of the conformance control strategy. Furthermore, the flow of NCF-CO2 foam in fractures significantly decrease the fracture permeability and the most noticeable reduction occurred at fg=0.67 (foam quality). This work, for the first time, demonstrates that the nanocellulose can be applied to effectively boost the scCO2 foam stability. In addition, the flow characteristics of this foam in fractures are investigated, which provides insights into conformance control for tight formations.