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MONTANA STATE UNIVERSITY ZERT RESEARCH
Modeling and Mapping at MSU Focus:
Monitoring at MSU Focus:
Mitigation at MSU Focus:
Modeling and Mapping Reservoir Heterogeneity Assessment Injection of CO2 into geologic formations has been practiced by the petroleum industry for enhanced oil recovery for several decades. Due to the economic incentives, established oil and gas infrastructure, and national interests in securing greater energy independence, Enhanced Oil Recovery (EOR) projects are the most likely candidates for initial large scale CO2 sequestration. However, significant hurdles to large scale sequestration must first be overcome through a significant research effort. It is not yet possible to predict with confidence storage volumes of CO2, injection efficiency of CO2, seal integrity and migration leakage pathways of CO2, and permanence of CO2 storage over geologic time periods. Many important issues dealing with geologic storage, monitoring and verification of CO2 in underground oil and gas reservoirs must be addressed. Pilot demonstrations are also needed to confirm practical considerations such as CO2 sequestration/EOR economics, project safety, CO2 stability and permanence in the subsurface environment, and public education and support for such projects. To be effective, joint CO2 sequestration/EOR projects will involve the injection of very large volumes of CO2 in close proximity to point sources or will utilize existing oil and gas pipeline infrastructure to move CO2 from point sources to suitable injection project areas. To accomplish this it is necessary to predict reservoir storage capacity, fluid flow efficiency in the reservoir as a function of stratigraphic and structural heterogeneity, potential leakage pathways from the reservoir, and the repeatability of the process from one field to the next within a petroleum system. To date, research concerning Enhanced Oil recovery (EOR) using CO2 injection and CO2 sequestration has been primarily at two disparate scales; (1) at the pore throat to individual field scale, and (2) at very large basinwide scales based on general screening criteria. An important body of research needs to be undertaken at the intermediate scale of individual fields to assessment units such that reservoir complexity and heterogeneity is documented in a systematic way that results in knowledge that can be applied to entire producing trends, assessment units, and petroleum systems. The research then provides for repeatable sequestration targets within a given assessment unit and provides important analogs for similar assessment units nationwide. Tremendous technological advances have been made in recent years that dramatically affect the ability to understand reservoirs at this intermediate scale. These include paradigm shifts in understanding the stratigraphy of sedimentary rocks as a function of changes in accommodation and rates of sediment supply, technological breakthroughs in the power of computer hardware and software for reservoir characterization, modeling, and simulation, and the acquisition and interpretation of three-dimensional seismic data. These advances have important implications to the study of CO2 sequestration. We can now better understand the three-dimensional variability of reservoirs and predict the behavior of fluids within these reservoirs than at any time in the past. Monitoring: DIAL Carbon Dioxide Monitoring Dr. Carlsten, Dr. Repasky, and Dr. Shaw There is clear need for sensitive methods of above ground monitoring for carbon dioxide leaks. Any such methods would also have application to monitoring Leaks in CO2 pipelines. One possible candidate is differential absorption lidar (DIAL), but because of the significant CO2 background and naturally occurring variations in atmospheric concentrations, it is desirable to leave the monitor in place for extended periods in order to get sufficient background data. This is incompatible with many current lidar systems that are very high priced and are typically only available for 1-14 days for any given measurement. MSU has pioneered the development of compact, low cost lidar systems based on diode lasers and MSU developed technology to control, shift, and tune the diode wavelength. Figure 1 illustrates the performance of a diode based lidar system developed at MSU for the measurement of water vapor. This system uses an external cavity diode laser and does not require wavelength shifting. The high resolution available makes it conceivable to detect isotopically labeled species. Carbon dioxide has strong absorption features at 2.0mm, 2.8mm, 4.4mm, and 4.8mm. Using the strong absorption features of the carbon dioxide molecule, an optical sensor is proposed for above ground monitoring. A schematic of the proposed sensor is shown in Fig.(2). The output from a continuous wave (cw) tunable laser is reflected from a retro-reflector, passes through a narrow band filter and is incident on a photo-detector. The laser is tuned across an absorption feature of the carbon dioxide and an optical power as a function of wavelength plot is generated. The amount of light absorbed is directly related to the number of carbon dioxide molecules in the beam path. Multiple retroflectors in a circular pattern and a turning mirror laser can be used to allow measurement over a larger area. A second carbon diode sensor will be placed away from the underground storage site and will be used to monitor background changes in the atmospheric carbon dioxide concentrations. Mitigation: Subsurface Biofilm Barriers This component of the research project focuses on developing strategies and technologies for controlling leakage of Supercritical CO2 during geologic sequestration. This project will examine the use of engineered microbial biofilm barriers as a method for reducing permeability of confining aquitard layers in the vicinity of CO2 injection and, likewise, providing a zone of reduced permeability to mitigate further migration of CO2 leaks which have penetrated the aquitard and reached overlying strata. Biofilm barrier technology involves the injection and subsurface transport of starved bacterial cultures followed by resuscitation with injected growth substrates. This process results in the production of copious amounts of extracellular polymer (EPS), which plugs the free pore space of the formation thereby reducing porosity and hydraulic conductivity. This zone of reduced hydraulic conductivity from a barrier which will serve as a means for controlling undesirable migration of contaminants including supercritical CO2. Biofilm barriers have been formed using a variety of bacterial species and conditions. Initial experiments were formed with an oilfield isolate of Klebsiella oxytoca under fermentative conditions and mesophilic temperatures. Barriers have been formed both in the laboratory and in field tests with Pseudomonas fluorescens under denitrifying conditions at lower temperatures (ca. 10°C). For microbial enhanced oil recovery (MEOR) we have formed barriers with Agrobacterium radiobacter under denitrifying conditions and mesophilic temperatures (20-25 °C). Temperatures expected in applications of biofilm barriers for supercritical CO2 injection range from 40-60°C. This is within the growth temperature range of moderately thermophilic bacteria (extreme thermophiles have optimal growth temperatures above 80°C). A wide variety of bacteria can grow at moderately thermophilic temperatures. Attractive aspects of biofilm barrier technology for enhancing geologic CO2 sequestration include: 1) biofilm barrier construction can be achieved without excavation and therefore may be useful at sites where access to the subsurface is restricted; 2) there is no obvious depth limitation with biofilm barrier technology; and 3) once established, the biofilm barrier requires minimal maintenance for long-term operation. The use of microbial biomass to plug free pore space in porous matrices was first exploited for microbial enhanced oil recovery by Jack, et. al. Research related to this application revealed that the production of extracellular polymers by bacteria was an important factor in permeability reduction and surveys were conducted to isolate polymer-producing bacteria that were tolerant of the high temperatures and salinities found in oil reservoirs. Enrichments conducted at moderately high temperature (50°C) and salinity (5%) produced a variety of isolates that produced extracellular polysaccharides. In a more recent survey of bacteria in high temperature petroleum reservoirs, a variety of fermentative bacteria were isolated from production waters of petroleum reservoirs with depths ranging from 396-3048 meters, temperatures ranging from 21-130°C, and salinities ranging from 2.8-128 g/L. Thermophilic fermentative microorganisms were successfully isolated from all production waters with salinity values of 40 g/L or less. In addition being able to grow at high temperatures and salinities, many species of microorganisms are adapted to growth at high pressures. Extremely barophilic microorganisms can grow at pressures exceeding 1000 atmospheres. These bacteria were isolated from deep ocean trenches. Bacteria isolated from deep-sea hydrothermal vents are capable of growing under extreme conditions of both temperature and pressure. Pressures expected in supercritical CO2 injection are more moderate (~100 atmospheres) and would thus require moderately barophilic or barotolerant bacteria. During pilot scale testing of MEOR, we have injected a polymer-producing strain of Agrobacterium radiobacter into an oil reservoir at pressures of over 100 atmospheres. This strain was isolated from water produced by the reservoir but was not specially selected for barotolerance. Overall, this research indicates that the temperature, salinity, and pressure expected in supercritical CO2 injection applications will allow the formation of biofilm barriers using appropriate species of bacteria.
ZERT is funded by the United States Department of Energy, under Award No. DE-FC26-04NT42262. However, any opinions, findings, conclusions, or recommendations expressed herein are those of the author(s) and do not necessarily reflect the views of the DOE. © 2005 Montana State University |
