Low-Cost, High-Performance Chemicals for Enhanced Oil Recovery

Abstract

The ability to select low-cost, high-performance surfactants for a wide range of crude oils under a wide range of reservoir conditions has improved dramatically in recent years. We have developed surfactant formulations (surfactant, co-surfactant, co-solvent, alkali, polymer, electrolyte) using a refined phase behavior approach. Such formulations nearly always result in more than 90% oil recovery in both outcrop and reservoir cores when good surfactants with good mobility control are used. Chemical flood residual oil saturations are typically less than 0.04 and surfactant retention between 0.01 and 0.1 mg/g with these formulations using as little as 0.2% surfactant concentration and 30% pore volume ASP slugs. We describe some of the advances that have improved the performance, reduced the cost, increased the robustness, and extended the range of reservoir conditions for these formulations. There are thousands of possible combinations of the chemicals that could be tested for each oil and each chemical combination requires many observations over a long time period at reservoir temperature for proper evaluation, so it would take too long, cost too much and in many cases not even be feasible to test all combinations. In practice we use our scientific understanding of how to match up the surfactant/co-surfactant/co-solvent characteristics with the oil characteristics, temperature, salinity, hardness and so forth. We have synthesized and tested new surfactants with much larger hydrophobes and more branching than previously available. We have tested new classes of co-solvents and cosurfactants with superior performance. These new developments have enabled us to develop good formulations for both oils that react with alkali to make soap and oils that do not. We have significantly lowered the chemical cost needed for waxy crudes with very high equivalent alkane carbon numbers. We have good results for oils with API gravities as low as 17, high temperature, high salinity, and high hardness brines. Many of these developments are synergistic and taken together represent a breakthrough in reducing the cost of chemical flooding and thus its commercial potential in both sandstone and carbonate reservoirs. SPE 129978ordered arrays such as gels or liquid crystals and decreases the reliance on alcohols or other co-solvents for rapid equilibration of microemulsions. Branched co-surfactants with different structures than the primary surfactant can be added to disrupt the orderly arrangement of surfactant molecules at interfaces (

Novel Large-Hydrophobe Alkoxy Carboxylate Surfactants for Enhanced Oil Recovery

“…Yang et al (2010) recently reported numerous ASP core flooding results for viscous oils. Viscous oils with low API gravity are usually active (contain organic acids that react with alkali to form soap) so the use of alkali reduces the surfactant cost and makes ASP flooding economically attractive under many circumstances.…”

“…When softening the injection water is not an option, chelating agents such as tetrasodium ethylene-diaminetetraacetate (EDTA-Na 4 ) can be used to sequester divalent cations, as reported by Yang et al (2010). However, EDTA-Na 4 is relatively expensive, and the required amount to complex divalent cations is higher than the theoretical value of 9 to 1 weight ratio as the temperature increases.…”

Alkaline Surfactant Polymer Flooding using a Novel Class of Large Hydrophobe Surfactants

“…. This effect can be understood using an activity diagram (Nelson et al, 1984;Zhao et al, 2008;Mohammadi et al, 2008;Yang et al, 2010). Furthermore, phase behavior experiments are used to determine the equilibration times and the quality of the microemulsion, such as microemulsion viscosities.…”

The Role of Co-Solvents and Co-Surfactants in Making Chemical Floods Robust

“…This is one of the most important requirements needed to achieve high oil recovery and low surfactant retention, and has been observed through core flood experiments (Dwarakanath et al, 2008, Yang et al, 2010. The surfactant solution in brine is often not clear near optimum salinity and may contain lamellar liquid crystals (Miller et al, 1986).…”