An experimental investigation of oil recovery in EOR processes in tight rocks

Unconventional oil production has become the largest source of oil production in the United States and is expected to continue for the foreseeable future. However, total oil recovery in these types of reservoirs is generally less than 10% of original oil in place. EOR treatments in the field have had mixed success and require further understanding for optimization at the field scale. Identifying the optimal treatment for these types of wells is difficult due to the low porosity (<5%) and nano-Darcy permeability which makes conventional methods of EOR and lab testing not feasible. In this study we will propose a new method for testing and comparing EOR treatments in tight rocks. By observing the oil in place from NMR before and after treatment, we can determine the most effective treatment method. In this study we analyzed three different formations: the Austin Chalk, Buda Limestone, and Eagle Ford Shale. Additionally, we tested different combination of treatment gases (nitrogen and carbon dioxide) and treatment fluids (brine, nano-activated, and nano-activated + surfactant). From the results of this work, we were able to identify the optimal treatment for each formation from the treatments that were tested. The experimental results were shown to be fast and repeatable. Additionally, the oil recovery results from each of the tested treatments were able to be easily compared (oil recovery ranged from 1% to 98%). By using a combination of treatment fluid and gas, the total incremental oil recovery increased when compared to gas only treatments. Lastly, we were able to identify the optimal treatment for each rock type by referring to the treatment with the greatest oil recovery.