Geophysical properties of carbon monoxide when used as an enhanced oil recovery agent

Abstract

ABSTRACT Many reservoirs witness decreased production related to the mobility of hydrocarbons given the composition of the fluids and rocks, and the reservoir environment (ie: temperature and pressure). Enhanced oil recovery (EOR) efforts attempt to manipulate these conditions to reach profitable production and prolong the economic viability of these known resources. Different approaches have been established for EOR, including steam and CO2 injection. While these methods have had widespread success in many reservoirs, there are various downfalls associated with each type of fluid injected into a reservoir. A primary concern with steam is the possible presence of swelling clays within the reservoir, in which the condensed steam will react with the clays and dramatically reduce the permeability. This reduction in permeability is a result of both clay fabric swelling, and the hydration of iron hydroxide within the clay structures surrounding the pore/pore throat in the presence of low salinity water. Carbon monoxide, however, has proven to be an effective iron reducer and successful in mitigating the clay swelling with respect to iron hydroxide hydration. It also exhibits phase properties that would allow the fluid to remain in the gas phase under temperature and pressure conditions that exceed other fluids' critical point, in turn aiding in time-lapse seismic monitoring by enhancing acoustic impedance contrasts of EOR fluids from liquid hydrocarbons to better define affected areas of the reservoir. Laboratory tests were designed to (1) investigate the acoustic phase properties of carbon monoxide compared to other common fluids, and (2) investigate the effects on permeability that carbon monoxide may have by reducing the swelling of clays. These tests were carried out with artificial sand packs in order to control the amount of swelling clays present in each sample being tested. The samples were outfitted with acoustic transducers and were ported at both ends to allow for fluid flow in and out of the sample. Measurements were taken while the samples were contained within a controlled temperature and pressure environment within conditions similar to those found in oil and gas reservoirs. A total of three individual samples were tested, the first being saturated only with brine, and the second two containing some amount of residual oil. Results indicate that carbon monoxide remains in the gas phase under pressure and temperature conditions that cause carbon dioxide to transition into the liquid phase, making it a desirable agent to seismically indicate where it is interacting with reservoir fluids. Observations made from flow tests indicate an average increase in permeability of roughly 130 -160% following the addition of carbon monoxide to a residual oil saturated sand pack.