Experimental Study of Enhanced Liquid Oil Recovery from Shale Reservoirs by Gas Injection

U.S. crude oil production has grown rapidly since 2011, which has been primarily driven by the production from shale and tight formations. The high oil production rate credited from horizontal drilling with hydraulic fracturing technique. However, those wells have steep decline rates over the first year or two. The initial stimulation treatments become less effective with the depletion in reservoir pressure. Recovery factors in liquid-rich shale and tight plays are typically quite low, less than 10%. In order to maintain or extend the oil production from existing wells, improved oil recovery (IOR) techniques must be considered to face the challenge. Gas injection is a developed and successful IOR technique for recovering oil from conventional reservoirs. The potential in shale formations have been investigated and highlighted by lots of recent publications. However, limited experimental studies were preformed to recover oil from nano-permeability shale samples. This project comprehensively evaluated the recovery performance and recovery process of cyclic gas injection (CGI), gas flooding, and cyclic water injection (CWI) in liquid-rich shale core samples respectively by performing experimental work. The objective was to screen the most effective method to achieve maximum oil production. The effects of soaking time, production time, and pressure depletion rate on the recovery efficiency of cyclic gas injection process were examined and analyzed in detail. For gas flooding, the core-scale simulation model was built to history match experimental data to study the recovery history and injection pressure effect. For cyclic water injection, the effects of soaking time and injection pressure on the recovery performance were examined and discussed. By conducting comparative study, it showed that the recovery performance of cyclic gas injection outperforms gas flooding and cyclic water injection.