Mechanistic Understanding of Microbial Plugging for Improved Sweep Efficiency
Theobjective of this project is the specific understanding of biofilm formation in porous media and its quantitative influence on sweep efficiency in microbial enhanced oil recovery (MEOR).
Petroleum & Geosystems Engineering, University of Texas at Austin, Austin, TX
Project researchers quantified the relationship between nutrient consumption and permeability reduction in laboratory systems. An important finding from this work was that the batch growth kinetics commonly measured to characterize microbial systems cannot be used to predict long term growth and nutrient uptake in a core. By extension, estimating performance at the field scale requires new models of the flow/transport/reaction coupling. The researchers developed a prototypical example of a suitably modified kinetics expression. They also successfully demonstrated conformance alteration by induced microbial growth. A core containing a high permeability layer of coarse beads and a low permeability layer of fine beads was inoculated with a microbial culture. The injection of nutrients caused microbial growth and consequent reduction in permeability. The high permeability layer accepted most of the flow initially. A tracer test after nutrient injection showed that microbe growth caused flow to become equalized between the coarse bead and fine bead layers. Further examination showed that the microbes grew exclusively in the high permeability layer, leaving the low permeability layer essentially undamaged
A better understanding of the processes of microbial growth in porous media will help industry improve sweep efficiency in MEOR-a novel enhanced oil recovery method that has the potential to add reserves and production in America's mature oilfields at low cost and with little environmental impact.
Simple plugging of thief zones by biomass (biofilm) growing on injected or in-situ substrates is the straightforward, achievable approach to MEOR. Yet there is a dearth of information on the fundamental processes of microbial growth in porous media, and there are no suitable data to model the process of microbial plugging as it relates to sweep efficiency. This research seeks to understand microbial growth in porous media and to identify parameters that can be used to model the effect of microbial plugging needed for sweep efficiency in U.S. oilfields.
The overall approach can be explained as the melding of the science of biofilm research with reservoir engineering design, the overall objective being to develop a quantitative procedure for assessing the likelihood of incremental oil production by microbial plugging of thief zones.
To quantify biofilm growth, Berea sandstone core columns are to be inoculated with a single, representative culture and evaluated for biofilm growth and permeability decreases. Growth will be monitored at varying flow rates and carbon substrate concentrations using assays of carbon substrate utilization (TOC, GC) plus biomass protein and using HXRCT imaging to observe biofilm architecture/geometry. Permeability changes will be followed by column pressure readings.
To model the effect of biofilm growth on permeability mechanistically, researchers use physically representative models of porous media to simulate the consequences of several modes of biomass growth at the grain scale. These include uniformly increasing biofilm thicknesses on all grain surfaces, preferential local growth of biofilms (e.g., in regions where local flow velocities are smaller), and nonuniform distributions of microorganisms.
A methodology was established for injecting nutrient into porous media inoculated with microbes while measuring nutrient consumption and permeability reduction continuously. Measurement of nutrient uptake in homogeneous cores was consistent only with qualitatively different kinetics of nutrient uptake measured in batch experiments. A modified version of microbial growth kinetics is therefore needed for predicting field-scale performance. Flow experiments in a heterogeneous porous medium revealed a new form of microbial growth behavior, which appears consistent with the phenomenon of quorum sensing. History matching the effluent histories from heterogeneous columns yielded porosity/permeability distributions that were consistent with strongly preferential microbe growth (and hence reduction in permeability and porosity) in the coarse bead layer. This supports the principal premise of this research project, namely that simple injection of nutrients, without any attempt to focus them into particular regions, leads to preferential occlusion of the higher permeability flow paths. If obtained at the field scale this would lead to improved sweep efficiency. The open question raised by this finding is the mechanism by which the microbes appear to carry out “quorum sensing” in a porous medium. This should be the subject of future research.
Current Status (January 2009)
This project has been completed and the final report is available below under "Additional Information".
Project Start: October 1, 2004
Project End: September 30, 2008
Anticipated DOE Contribution: $594,524
Performer Contribution: $188,631 (24% of total)
Other Government Organizations Involved: Lawrence Berkeley National Laboratory
NETL - Chandra Nautiyal (firstname.lastname@example.org or 918-699-2021)
U. of Texas - Steve Bryant (email@example.com or 512-471-3250)
Final Project Report [PDF-1.80MB]
Bryant, S., “Preferential Growth of Biofilms in Heterogeneous Porous Media,” Society of Industrial and Applied Mathematics Conference on Mathematical and Computational Issues in the Geosciences, Santa Fe, New Mexico, 20-22 March 2007.
Bryant, S., "Microbial Enhanced Oil Recovery (MEOR)," Chemical Enhanced Oil Recovery (EOR) Workshop, Center for Petroleum and Geosystems Engineering, University of Texas, Austin, Texas, April 27, 2006.
Gandler, Greg. Mechanistic Understanding of Microbial Plugging for Improved Sweep Efficiency. MS Thesis, The University of Texas at Austin, May 2006.
Gbosi, Akpobari. Parameter Modeling for a Mechanistic Understanding of Microbial Plugging. MS Thesis, The University of Texas at Austin, August 2007. Gandier, G., Gbosi, A., Bryant, S.L., and Britton, L.N., Mechanistic understanding of Microbial Plugging for Improved Sweep Efficiency, SPE 100048 presented at Fifteenth SPE/DOE Improved Oil Recovery Symposium, Tulsa, OK, April 2006.
Bead packs as shown above are 1 cm in diameter and 15 cm long. All experiments involved single phase flow of brine or nutrients. Plastic end units threaded to accept Teflon unions to prevent microbe growth outside the column.
Epoxy-confined core in conjunction with temperature-controlled oven allows in-line analysis of nutrient uptake by microbes in the core. Note that the core is outside the oven. The microbes thrive at room temperature but not at elevated temperature, so all pumps, vessels, and flow lines are kept inside the oven to prevent reaction anywhere except inside the core.