Experimental Investigation of Enhanced Recovery in Unconventional Liquid Reservoirs using CO2: A Look Ahead to the Future of Unconventional EOR

Abstract

The poor rock quality and matrix permeability several orders of magnitude lower than conventional oil reservoirs observed in unconventional liquid reservoirs (ULR) presents many uncertainties on the storage capacity of the rock and the possibility of enhancing recovery. The technological advances in multiple stage hydraulic fracturing and horizontal drilling have improved the overall profitability of oil shale plays by enhancing the matrix -wellbore connectivity. The combination of these technologies has become the key factor for the operators to reach economically attractive production rates in the exploitation of ULR, causing a lot of focus on their improvement. However, as the reservoir matures, primary production mechanisms no longer drive oil to the hydraulic fractures, making the improvement of matrix -wellbore connectivity insufficient to provide economically attractive production rates. Therefore, the need to develop enhanced recovery techniques in order to improve the displacement of the oil from the matrix, maintain profitable production rates, extend the life of the assets and increase ultimate oil recovery becomes evident.This study presents experimental results on the use of CO 2 as an enhanced oil recovery (EOR) agent in preserved, rotary sidewall reservoir core samples with negligible permeability. To simulate the presence of hydraulic fractures, the ULR cores were surrounded by high permeability glass beads and packed in a core holder. The high permeability media was then saturated with CO 2 at constant pressure and temperature during the experiment. Production was monitored and the experiment was imaged using x-ray computed tomography to track saturation changes inside the core samples.The results of this investigation support CO 2 as a promising EOR agent for ULR. Oil recovery was estimated to be between 18 to 55% of OOIP. We provide a detailed description of the experimental set up and procedures. The analysis of the x-ray computed tomography images revealed saturation changes within the ULR core as a result of CO 2 injection. A discussion about the mechanisms is presented, including diffusion and reduction in capillary forces. This paper opens a door to the investigation of CO 2 enhanced oil recovery in ULR.

Experimental study of core size effect on CH4 huff-n-puff enhanced oil recovery in liquid-rich shale reservoirs

“…The CT scan method is considered to be a nondestructive method to measure the cores' porosity, gas or oil saturation, and lithology characteristics within the cores (Siddiqui and Khamees, 2004;. The CT scan method has been widely used in petroleum engineering applications for describing the core porosity (Siddiqui et al, 2005), relative permeability (MacAllister et al, 1993), investigating the performance during core flooding experiments (London, et al, 2014), or other EOR processes (Kovscek et al, 2008;Simjoo et al, 2013;Tovar et al, 2014;. For this study, core plugs were scanned during the huff-n-puff tests to reflect the gas or oil saturation changes inside the core, and to help calculate the oil recovery in different stages.…”

Experimental study of permeability reduction and pore size distribution change due to asphaltene deposition during CO2huff and puff injection in Eagle Ford shale

“…Gamadi et al firstly did an experimental study on nitrogen huff and puff injection in shale oil rocks, and results showed a high oil recovery factor. Similar huff and puff experiments were carried out using CO 2 as the injection gas and showed good oil recovery factor in shale cores . Wan et al firstly simulated huff and puff gas injection in a hydraulic fractured shale reservoir using black oil models, and the results showed the oil recovery was improved to 29% by huff and puff gas injection compared with the primary recovery 6.5% from primary depletion.…”

Modeling Interwell Fracture Interference and Huff-N-Puff Pressure Containment in Eagle Ford Using EDFM

“…Experimental results have exhibited that diffusion of injected gas into unconventional oil reservoirs is possible, but difficult to estimate (Vega et al, 2010;Hawthorne et al, 2013;Tovar et al, 2014). Furthermore, gas-into-liquid diffusion is much slower than gas-intogas diffusion.…”