Enhanced oil recovery from Sandstones and Carbonates with “Smart Water”

Abstract

According to the International Energy Agency crude oil is expected to contribute approximately with 26% of the world’s energy supply by 2040. In a per year basis, new oil discoveries have dropped to a 60-year low in 2015, and capital expenditure is in the longest period of retrenchment in 40 years. Therefore, oil in place from already discovered reservoirs has become an important target for oil companies.

“Smart Water” injection is a relatively new EOR method that improves oil recovery by wettability alteration in both sandstones and carbonates. It disturbs the established chemical equilibrium in the reservoir causing wettability alteration, and during this process, capillary forces increase and water imbibition occurs, resulting in improved microscopic sweep efficiency. The EOR potential is affected by the initial reservoir wetting condition, which is dependent on parameters like mineralogy, formation water composition and crude oil. The same parameters also influence the wettability alteration process. The optimum conditions for observing “Smart Water” EOR effects appear to be mixed-wet conditions.

The objective of this work was to improve the understanding of the initial wetting and wettability alteration in sandstones and carbonates by studying the interactions among the different phases involved in these processes. Furthermore, maturing and gaining confidence with the screening techniques for evaluation of the “Smart Water” EOR potential was also an important part of the project.

Focus was made on explaining the role of the mineralogy in the wetting mechanisms and the “Smart Water” EOR potential in a range of lithologies. A correct mineralogical characterization plays an essential role in the selection of the “Smart Water” brine.In the case of sandstones, the effect of formation water and “Smart Water” brine compositions were studied, the observations indicated that both formation brine and injection brine compositions are factors that can influence the “Smart Water” EOR potential. By studying the temperature effect in cores containing reactive plagioclase minerals, it was found that the overall low salinity “SmartWater” EOR effect was not affected by temperature. Additional studies on injection strategies were carried out, and the results confirmed that low salinity “Smart Water” EOR effects are dramatically improved if injected in secondary mode, as opposed to tertiary mode.

The experiments carried out on a carbonate reservoir system showed that for limestone and dolomitic limestone, “Smart Water” EOR effects could also be observed at the challenging low reservoir temperature of 65 °C. The selection of the “Smart Water” composition was crucial to observe the EOR effects, and accurate mineralogical analyses were fundamental for the suitable selection.

Confidence was gained in the implementation of screening techniques for identifying positive and negative scenarios linked to “Smart Water” EOR potential in sandstones and carbonates. The combination of different experimental techniques can rapidly indicate a high or low “Smart Water” EOR potential for a reservoir. A valuable relationship was observed between the screening methods and the amount of oil produced by “Smart Water” injection. However, quantitative information about improved oil recovery with “Smart Water” can only be determined by running oil recovery tests.

In light of the current reservoir chemistry knowledge, this experimental work constitutes a summary of the present understanding of “Smart Water” EOR processes. Hopefully, this work may also serve as a simple guide for evaluating “Smart Water” EOR processes.