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Harpalani, Satya

Publications and source records attributed to Harpalani, Satya.

11 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Understanding poromechanical response of a biogenic coalbed methane reservoir

Abstract Biogenic coalbed methane (BCBM) reservoirs aim to produce methane from in situ coal deposits following microbial conversion of coal. Success of BCBM reservoirs requires economic methane production within an acceptable timeframe. The work reported here quantifies the findings of previously published qualitative work, where it was found that bioconversion induces strains in the pore, matrix and bulk scales. Using imaging and dynamic strain monitoring techniques, the bioconversion induced strain is quantified here. To understand the effect of these strains from a reservoir geomechanics perspective, a corresponding poromechanical model is developed. Furthermore, findings of imaging experiments are validated using core-flooding flow experiments. Finally, expected field-scale behavior of the permeability response of a BCBM operation is modeled and analyzed. The results of the study indicated that, for Illinois coals, bioconversion induced strains result in a decrease in fracture porosity, resulting in a detrimental permeability drop in excess of 60% during bioconversion, which festers itself exponentially throughout its producing life. Results indicate that reservoirs with high initial permeability that will support higher Darcian flowrates, would be better suited for coal bioconversion, thereby providing a site-selection criteria for BCBM operations.

Pandey, Rohit (ORCID:0009000415483436)↗
DOE OSTI2021

Geomechanical and flow implications with continued bioconversion of coal to methane: Experiments and modeling

Microbial conversion of coal to methane is a promising technology during transition of coal-based energy from conventional coal mining to natural gas recovery from coal. Significant research advances have been made towards engineering ideal microbial communities and nutrients for bio-stimulation of coal. However, actual field applications require geomechanical and flow behavior characterization of coal during the bioconversion process as well as gas production over the life of the created “biogenic gas reservoirs”. This work presents the results of an experimental investigation to estimate gas/methane production using bioconversion of coal and analyses of variations in bulk modulus, strain and permeability. Bulk modulus of coal demonstrated time-dependent behavior with continued bioconversion of solid coal. The phenomenon was modeled using mass balancing in a closed environment and the logistic equation based biogenic gas production with time. The modeled gas production and changes in modulus of coal showed excellent agreement with the corresponding experimental results. Next, numerical simulation of biogenic conversion of coal in a constant stress in-situ condition, replicating the Huff ‘n Puff method under field conditions, was carried out. The results showed that bioconversion can lead to decrease in effective stress, increase in permeability and decrease in the modulus of coal with time. Repeated recharge of coal with nutrients and recovering the produced gas, that is, sequential cycles of Huff n’ Puff, showed further increase in permeability and decrease in coal strength, potentially leading to coal failure in-situ, further increasing the permeability, thus enhancing the prospect of field application of the technology.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2018

A Scaling Study of Microbially-Enhanced Methane Production From Coal (Mecbm): Optimizing Nutrient Delivery For Maximized Methane Production

Microbially-enhanced coalbed methane (MECBM) recovery is a novel method to stimulate gas production in CBM reservoirs. We first develop suitable nutrient recipes for native coals from sites each in the Illinois Basin and in the San Juan Basin. The optimal concentrations for statistically significant parameters are identified and the methane yields at laboratory scale are obtained (Part I & II). We then demonstrate the importance of replicating truly in-situ conditions for bio- gasification studies by investigating methane productivity in a core holder simulating in-situ conditions. Based on the experimental results, the resulting gas production correlates positively with the permeability of the samples. We examine the deliverability of engineered microbial solutions to promote coal bioconversion in coals and demonstrate that greater than milli-darcy permeability is required under in-situ stress conditions (Part III). This constraint is supplemented by imaging and a fractal-based characterization approach to evaluate changes in the physical properties of coal due to bio-gasification. High resolution SEM imaging is used to observe swelling of the coal matrix with sub-micron wide continuous pores observed to persist even after microbial treatment (IV). We explore the potential of generating, propping-open and sustaining the functionality of hydraulic fractures in coal using different fracturing fluids (Part V). The alteration of the nano-pore structure due to MECBM treatment is examined by using small angle X-ray scattering (SAXS) to define the in-situ porosity evolution as a proxy to infer permeability evolution (Part VI). Coupled hydro-mechanical and bio-gasification modeling is applied to determine the effectiveness of nutrient delivery by hydraulic fracturing and its field implementation. Compared with both the unstimulated and hydro-shear-dilated cases of the natural fracture network, hydraulic fracturing demonstrates a significant improvement to enhance nutrient delivery. A preliminary analysis of field-scale methane yield is completed with consideration of the combined influence of permeability evolution, solute transport and microbial growth (Part VII). Developing nutrient solutions for Illinois Basin and San Juan Basin (Task 2): To enhance methane release from coal through bio-gasification, suitable nutrient solutions are needed to stimulate microbial activities toward coal depolymerization and conversion to biogas. Specific for bituminous coal in the Illinois basin, a nutrient recipe that can be used to enhance coal bio- gasification in situ is developed. Based on our previous experience working with Illinois coal and the characteristics of the formation water and the indigenous microbial community, four parameters, Fe powder, methanol, ethanol, and trace minerals are optimized through using a Box-Behnken design. The optimal condition predicted by the models is: Fe-powder at 74 mM, methanol at 97.91 mM, ethanol at 100 mM, and trace minerals at 100%. Under these conditions, the predicted methane yield and content is 1,417.35 ft 3 /ton and 80.7%, respectively. These results are then validated by experimental studies. In addition, each added component is evaluated in terms of its contribution to methane generated. Specifically, the role of coal in the bio-gasification process is studied against two other solid materials. Experimental data from different solid matrices prove that coal is indeed degraded by the studied microbial community.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2018

An imaging and fractal approach towards understanding reservoir scale changes in coal due to bioconversion

Microbially enhanced coalbed methane (MECBM) aims to replicate the natural process of microbial methane generation in coal under in situ conditions. Considerable work has been reported over the years to optimize the associated microbial geo-chemistry. However, there is very little insight with regards to changes in the physical structure of coal due to bioconversion, and its impact on fluid flow properties. Here this paper presents the result of an image and fractal-based approach used to evaluate the changes in physical properties of coal. Samples of coal treated over 30, 60 and 120 days respectively were imaged before and after bioconversion. The results revealed that coal bioconversion resulted in swelling of the coal matrix. Cleats narrower than 5 µm reduced in its width post-bioconversion. A 77% drop in the permeability of coal is expected from the obtained results. Bioconversion also resulted in separation of thin layers of coal flakes from the coal surface, serving as a potential source of fines. Fractal analysis of the images revealed a decrease in the fractal dimension post bioconversion, which is in agreement with the previously reported studies, thus corroborating the variations in sorption-trends observed due to bioconversion. Additionally, the methodology to determine the fractal dimension via two-dimensional image processing was modified to improve its accuracy, and remove the dependency of the dimension to the scale of the obtained images. Bioconversion also resulted in formation of new pores/fractures. Shorter treatment duration resulted in nanometer-scale discontinuous pores, which do not contribute to Darcian flow. Longer treatment periods resulted in sub-micron wide continuous pores. Also, few larger fractures (>5 µm wide) saw an increase in its aperture post-treatment. This opens up new avenues, such as, utilizing artificially induced fracturing techniques to enhance biogenic methane production in future.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2017

A formation water-based nutrient recipe for potentially increasing methane release from coal in situ

Biogasifying coal to methane represents an environmentally benign way to utilize the abundant and inexpensive coal resource. To increase methane yield from coal, numerous studies have investigated the approach of biostimulation through finding the best nutrient solutions to enhance microbial activities. Toward this end, however, almost all studies have adopted laboratory made medium that is tap water- or deionized and distilled water- based. As a matter of fact, this water is dramatically different from formation water in coal basins. Thus, in order to enhance methane release from coal in situ, this study aimed to design a formation water-based recipe. To accomplish this objective, the chemical and microbial compositions of the formation water collected from the San Juan basin were analyzed first. Equipped with this fundamental knowledge, a screening test was conducted to evaluate nine parameters to identify statistically significant ones affecting methane yield from coal. For those critical parameters, the optimal value for each was determined through response surface methodology. Finally, the predicted results by the models were verified by an experimental study adopting all optimum conditions. Here this study demonstrated that microbes capable of converting coal to methane were present at the San Juan basin and the developed recipe increased methane yield 24.3-fold compared to those without.

01 COAL, LIGNITE, AND PEAT↗