Further Investigation of Forced Imbibition in Unconventional Oil Reservoirs for Enhanced Oil Recovery

Abstract

One of the popular EOR methods for unconventional oil reservoirs is taking advantage of the spontaneous imbibition during the completion stage of a multistage hydraulic fractured horizontal well. An abundant amount of completion fluid is injected during the operation and is expected to boost oil production through counter-current imbibition before the well opens for production. While most similar studies focused on modeling the spontaneous imbibition, this process occurs with soaking pressure involved in real life, which is defined as forced imbibition. Our previous study discussed the mechanisms and demonstrated the difference between spontaneous imbibition and forced imbibition through experiments and numerical simulation. The soaking pressure negatively impacts the efficiency of imbibition due to a high-pressure barrier, which further impairs the production enhancement. This study further investigated factors that may affect the recovery during this soaking stage in a more realistic reservoir model. The model is validated through lab experiments and mimics a quarter of a hydraulic fracturing stage. The effects of cluster spacing, permeability, and wettability were studied under different soaking pressures. The results indicated that, regardless of the soaking pressure, imbibition is an effective method to enhance the recovery of an unconventional oil reservoir. The results are highly sensitive to the cluster distances and only effective within the stimulated reservoir volumes. The matrix permeability and wettability are also important factors to be considered. The objective is to provide a better picture for the accurate design of fracturing completion so that an optimum oil production enhancement can be achieved.