Reports: ND849823-ND8: Using Geo-electrical Methods as a Monitoring Aid for Microbial Enhanced Oil Recovery

Dimitrios Ntarlagiannis, PhD, Rutgers, the State University of New Jersey (Newark)

The objective of this project is to investigate the sensitivity and applicability of geo-electrical methods for high resolution temporal and spatial monitoring of microbial enhanced oil recovery (MEOR) processes. It is important to note that although the use of such methods has been proposed in the past, there has never been a conclusive study on the applicability of the methods. The approach taken in our research is to perform laboratory experiments of MEOR processes while geophysically monitoring the progress. The 1st year experiments confirmed that the spectral induced polarization (SIP) method can qualitatively monitor MEOR related changes in laboratory experiments. The 2nd year efforts (this reporting period) focused on a) the detailed analysis and interpretation of already existing data, and b) new laboratory experiment on the quantitative interpretation of MEOR processes using the SIP method.
Experimental Progress. The first full experimental cycle showed that geophysical measurements are indeed sensitive to MEOR processes. A consistent and steady change of geophysical parameters was recorded during the columns were microbialy active; no signals were recorded for the control column. The raw geophysical data were successfully processed used a phenomenological model, termed Debye Decomposition (DD); this process derived global measures of the geophysical parameters of interest, namely the chargeability magnitude (m) and time constant (t); the former (m) clearly showed that geophyical signal change as a response to MEOR processes in our system.
During the 2nd year of the project column fluids that were appropriately stored were further analyzed to confirm that the MEOR treatment was successful. More specifically the chemical composition of the inflow and outflow samples were determined by Gas Chromatography-Mass Spectrometry (GC-MS). After treated, the samples were derivatized and analyzed on an Agilent 6890N Network GC system. Data was analyzed using MSDChem software.
Analyses of the samples indicate differences in the chemical profiles of the MEOR active columns compared to the control column. The complexity of the profiles decreased from over the course of the experiment in both active columns, whereas there were only minor differences in the composition of the low intensity peaks present in the profiles of the control column. This variation in the control column was likely due to concentrations that were at or below the detection limit of the instrument. There was a noticeable loss of high molecular weight alkanes (greater than 16 carbons) in the end point outflow sample of Active column 1 compared to the starting point samples. Same alkanes were detected in the Control column ouflow samples at both the start and end point of the experiment, suggesting that the lack of alkanes in the late outflow samples in the Active 1 correlates with biological degradation of oil constituents. Active 1 also showed fatty acids of less than 16 carbons in the early time point, which either disappeared or were present in a lower abundance at the end of the experiment. There were some fatty acids of 16-18 carbons in length that were present at both the beginning and end of the experiment in both active columns. These peaks did not show a significant change in peak intensity, and were most likely entering the column as part of the ParaBac/S growth medium. The above described results verified that the MEOR active columns were successfully treated and MEOR processes did occur.
The processing/interpretation of the 1st experimental cycle is complete and submission for publication at GRL (AGU journal) is pending.
Furthermore we designed and executed the 2nd experimental cycle, aimed at quantitative interpretation of the SIP signals during MEOR processes. The 2nd experiment followed the same basic layout of the initial experiment with some important modifications:
use of specific microbial species for enhanced oil degradation processes to better monitor the microbial and geochemical evolution of our system.
columns were made in 4 replicates (total of 20 columns, 12 active, 8 control) to allow for destructive analysis of the full column material during the experimental cycle and not only after the end of the experiment
Based on the first experimental cycle we identified a microbial species, R. ruber, best fitted for our experiments. Batch experiments confirmed that R. ruber can degrade our heavy oil. We inoculated 12 columns with R. ruber (4 columns used modified growth medium to investigate the effect on MEOR processes) and we kept 8 columns as control. Although significant effort has been put into the experimental design the results were not satisfactory. The main problem we anticipated was to keep the system sterile from outside microbial contamination – these efforts were unsuccessful mainly due to the large number of columns fed from the same saturating solutions and the need for accurate geophysical measurements (maintenance of electrodes led to pathways for contamination). The second experimental cycle terminated after 5 months of columns operation.
Current and future work. The 2nd experimental cycle has been redesigned and will be repeated. We have modified the geophysical columns to be used to correct for the contact resistance problems; we will also use a smaller number of columns (6) that we believe it is easier to maintain sterile, while giving us the opportunity to further study the quantitative links between SIP signals and MEOR processes.
Although our previous efforts on mathematically describing the physical meaning of the SIP signals during MEOR projects were hindered by the unsuccessful 2nd experiment we plan to continue our efforts on adapting existing mechanistic models to describe the SIP response of MEOR processes.
Impact. Jeffrey Heenan, supported under this grant, successfully continues his efforts towards a PhD degree.
Alan Lepera was an undergaduate student at Rutgers – Newark that was exposed to the experiment, helped Jeffrey with laboratory work and familiarized himself with the SIP method along with standard laboratory procedures.
This project also benefited my career. I am still very active on this front. The results so far are being used to understand similar processes in the field under existing research projects. More exciting is the fact that the oil industry expressed interest in funding the continuation of such experiments.