High levels of dissolved oil and heavy metals in produced water hinders the utilization of conventional membrane filtration technologies to treat produced water for its beneficial use (e.g. integration into industrial and agricultural use) and/or safe disposal. The goal of this research is 1) to assess the feasibility of removing dissolved oil from produced water by stimulating the activity of indigenous oil degrading microbial communities, and 2) to determine the potentiality of removing heavy metals and naturally occurring radioactive materials (NORM) from produced water by using compressed dolomite filters made of powdered dolomites. The potentiality of this new treatment methods of produced water lays on our following findings and practical considerations: 1) produced harbors anaerobic microbial communities that are well adapted to high salinity conditions, 2) dolomites represent a superior sorption capacity for heavy metals than other natural sorption materials, 3) produced storage tanks can be readily adapted to operate as anaerobic bioreactors, and 4) high purity dolomites are abundant in the Arbuckle Group of Oklahoma and Kansas.
2. Understanding the relationship between the pore microstructure and flow properties of carbonate reservoir rocks
Although it is generally agreed that flow properties of carbonate reservoir rocks are function of the pore microstructure (size distribution, geometry, and connectivity of pores), a predictive understanding of the relationship between the pore microstructure and flow properties of carbonate sedimentary rocks is yet to be developed. The goal of this research project is to develop a predictive understanding of the relationship between the pore microstructure and flow properties of carbonate reservoir rocks. To reach this goal, we are researching a novel approach that consists of the stochastic reconstruction of pore microstructures using pore size distribution curves obtained from nuclear magnetic resonance (NMR) T2 measurements and pore/grain geometries obtained from scanning electron microscopy (SEM) analysis. This approach will allow us to reconstruct several pore microstructures of the same and pore size distribution but random pore connectivity. This property of the reconstructed pore microstructures will enable us to focus on the effect of pore connectivity and its stochastic nature on the flow properties of carbonate sedimentary rocks. The analysis will be done by conducting pore-scale simulations of important flow properties such as permeability and tortuosity.
3. Coupling of geological carbon storage (GCS) and microbial enhanced oil recovery (MEOR) through the stimulation of microbial methanogenesis
Multiple studies on the impact of CO2 injection on microbial communities of deep saline aquifers have shown that indigenous microbial communities including methanogenic microbes can adapt to the extreme conditions of GCS. The goal of this research project is to couple geologic carbon sequestration (GCS) and microbial enhanced oil recovery (MEOR) by stimulating the microbial conversion of crude oil (mostly n-alkanes) and CO2 to CH4. Our preliminary experimental and computational results have shown that this can be achieved by combining the injection of CO2 and produced water supplied with protein-rich matter. We are conducting parallel experimental and computational studies using rock, formation water, and crude oil samples collected from the Stillwater and Cushing oilfield of Oklahoma. One important feature of this new CO2-MEOR method is that methanogenesis occurs preferentially via the reduction pathway of CO2. Therefore, we expect that this research will lead to the establishment of an economically viable industrial method to biogenically recycle CO2 to CH4 and enhance oil recovery from depleted oil reservoirs, changing society’s perception of GCS as being an expensive alternative to reduce CO2 emissions into the atmosphere.
4. Computational modeling and simulation of geological carbon sequestration (GCS) under biotic conditions
Available software to simulate geological carbon storage (GCS) does not account for the effect of microbial activity on the fate of CO2 in GCS sites. The goal this research project is to assess the long-term physical, chemical, and microbiological fate of CO2 in deep saline aquifers and depleted oil reservoirs injected with CO2, where the availability of nutrients and/or the co-injection of produced water supplied with nutrients can result in the microbial conversion of CO2 and/or residual crude oil to CH4. To this aim, we have developed a new TOUGHREACT module named CO2Bio. TOUGHREACT-CO2Bio can simulate the multiphase flow of CO2-CH4-H2S-H2 gas mixtures and brine in deep saline aquifers and depleted oil reservoirs under biotic conditions. The next step is to account for the mobility the crude oil due to pressure restoration and/or viscosity reduction.
5. Understanding the mobility and transport of heavy metals in deep saline aquifers
The mobility and transport of heavy metals present in produced water disposed into deep saline aquifers is unknown. The goal of this research project is to provide new knowledge and computational tools to predict the chemical and physical fate of heavy metals in deep dolomite saline aquifers where produced water is commonly disposed in Oklahoma. So far, we have developed new knowledge and computational tools to predict the mobility and transport of barium in deep dolomite aquifers. The established combined experimental and computational approach can be used to design effective injection schemes to prevent the contamination of underground sources of drinking water (USDW) due to the migration of produced water through natural fractures/faults and failures of abandoned oil wells. The next step is to conduct experimental and computational studies to predict the mobility and transport of other heavy metals (e.g. Sr, As, B, and Br), NORM, and organic hydraulic fracturing additives (e.g. guar gum, polyacrylamide, and glutaraldehyde).
6. Pore-scale simulations of flow properties of carbonate reservoir rocks using pore microstructures at the nano-scale level
Besides a consistent kinetic model for the dissolution/precipitation and aqueous phase reactions of solutes, and a suitable equation of state (EOS) to represent the solubility of gases in the aqueous phase, the use of multiphase reactive transport simulation programs needs of accurate information on the flow properties of the reservoir rock. We are using FIB-SEM techniques and the capabilities of CFD simulation programs (COMSOL Multiphysics) to reconstruct the microstructure of reservoir rocks and conduct pore-scale simulations of flow properties of reservoir rocks at the nano-scale level. For instance, we have found that effective diffusivity (Deff) values of reactive species estimated from pore-scale simulations are different to those estimated from widely employed empirical expressions (e.g. τd = ϕ Dm/Deff) which only account for the tortuosity (τd) and porosity (ϕ) of the reservoir rock. The next step is to estimate Deff values of reactive species for multiphase flow systems. Pore-scale simulations of single and multiphase flow systems will be used to formulate more accurate effective diffusivity expressions, which will improve predictions made by field-scale reactive transport simulations.
PAST RESEARCH PROJECTS
7. Microbial enhanced hydrocarbon oil recovery (MEHR) through selective plugging of high permeability zones
Microbial growth and their biogeochemical reaction products can lead to significant changes in porosity and permeability of reservoir rocks. Reduction in porosity and permeability may be caused by the growth of microbes and the deposition of extra-polymeric substances (EPS) in the void space of rocks, whereas an increase in porosity and permeability may occur due to the dissolution of rocks accelerated by produced organic acids during microbial growth. The objective of this research was to develop reactive transport models to mechanistically understand the complex interplay between microbial growth, EPS production, and the interactions between the microbial byproducts and rocks. This research can help to identifying the controlling factors that govern the selective plugging of oil and gas reservoirs to enhance hydrocarbon recovery, on a case-by-case basis.
8. Biodegradation of spilled oil in sea water
After or during the oil spill it is of common practice to introduce chemical dispersants near the spill region. Under these conditions, spilled oil can not only dissolve in sea water, but also form oil droplets. Although large oil droplets can arise to the sea surface due to the buoyancy effect, previous studies suggest that small oil droplets would not rise to the surface but remain in underwater. Thus, spilled oil can exist in both dissolved form and as oil droplets in deep water. To be able to predict the biodegradation rate of the fraction of oil in the form of droplets, I developed a new model for the biodegradation kinetics of dispersed oil droplets. The next step is to couple flow and transport processes with biodegradation to explicitly simulate the evolution of oil composition with time to more accurately represent what occurs after oil spills.
9. Heavy oil upgrading with supercritical water
If heavy crude oil resources are to be exploited, efficient, environmentally benign and inexpensive upgrade technologies are desirable. To fulfill these conditions, upgrading without coke formation is required, and supercritical water processing is an attractive option to achieve this aim. Specific features of potential supercritical water processes have been reported: the yield of asphaltenes and resins can be reduced; the fraction of aromatics is reduced, while the yield of saturated compounds is increased; in addition the removal of sulfur, nitrogen and metal fractions is possible. The results of this research suggested that supercritical water serves both as a reaction medium, and a reactive species, and thus the supercritical reaction atmosphere may provide effective upgrading conditions for heavy oil without the need for a catalyst. The next step would be to design and optimize the operation of a counter flow reactor.
10. Heap and underground leaching of minerals
The main objective of this research was to elucidate the catalytic effect of thermophiles in leaching sulfide minerals. I made various new findings regarding the chemical, physicochemical and microbiological factors that control the leashing of sulfide minerals. To bridge laboratory results and field applications, I have developed novel kinetic models and advanced mathematical models to assess the auto-thermal performance of heap and underground leaching systems. The methodologies employed in this research can be used to assess the impact of microbial activity on the leaching of heavy metals from shale gas rocks at deep geological formation conditions. This type of information is important to assess possible formation damages of producing zones, and mobilization of heavy metals.