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Oil Reservoir & Environmental Technologies

Improved Waterflooding and Wettability

This project will obtain a more complete understanding of the effects of brine composition, temperature, and crude oil properties on wettability and its effects on oil recovery. It has been shown for sandstone and several crude oils that changes in brine composition can result in differences in waterflood recovery of 15 to 50% of original oil, in place. These results will be confirmed for outcrop and reservoir cores of different mineralogy and pore structure (e.g. sandstones with varying clay content, and carbonates), and a broader range of crude oils. The final product will be a theory, backed by laboratory experiments and field evaluation, that can be used by operators (major and independent) to improve waterflood oil recovery from specific reservoirs. By changing the injected brine chemistry, we will manipulate wettability to develop a cost-effective improvement in oil recovery efficiency.

Waterflooding is by far the most widely applied method for improved oil recovery. It accounts for more than one-half of U.S. domestic oil production. Similar proportions hold worldwide. The brine injected into a waterflood, which is usually of different composition than the connate water, is obtained from the most convenient source. The treatment of injected water and the modification of its composition are dominated by considerations relating to avoiding formation damage and mitigating souring and corrosion. It has been generally believed that the composition of injected brine is immaterial to the efficiency of oil displacement. A growing body of laboratory data, however, shows that the brine composition can have a highly significant effect on crude oil, brine, and rock interactions, as evidenced by oil recovery by waterflooding and spontaneous imbibition. Although results strongly depend on crude oil composition, this trend has been observed for three distinctly different types of crude oil (i.e. an asphaltic crude oil, a highly waxy crude oil, and a crude oil with extremely low asphaltene content). Changes in oil recovery with cation valency and radius of hydration have also been observed. Crude oil properties, particularly the solvency of high molecular weight polar components and modest increases in temperature, also have a major effect on crude oil, brine, and rock interactions and oil recovery.

In addition to changes in oil recovery, corresponding changes in the wettability of the system are also clearly demonstrated. Selection or adjustment of injection brine composition in a way that advantageously alters wettability is a novel method of increasing oil recovery at potentially low cost. The goal of this project is to develop processes that will allow the timely and effective implementation of this technology to increase oil recovery from producing oil fields and to make it available to field operators. Currently, we are endeavoring to verify laboratory results with field data, and we are looking for partners to test this improved waterflooding method in a future waterflood. One option for a field test would be to flood one portion of the reservoir with an optimized water composition, flood the other portion of the reservoir with water from a generic source, and then compare recoveries from the two floods. An alternative would be to convert an existing waterflood that is using a normal field brine as source water to a fresh water or dilute brine flood.

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DOE Office of Nuclear Energy
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