|Kinetic Parameters for the Exchange of Hydrate Formers
||Last Reviewed November 2016
This project will investigate the kinetics associated with producing natural gas from hydrate bearing geologic media via unconventional technologies. The principal production technology of concern for this research will be that of exchanging carbon dioxide (CO2) and nitrogen (N2) with clathrated methane (CH4). The so called guest-molecule exchange technology is an attractive technology from the perspective of its potential for maintaining the geomechanical integrity of the reservoir formation, in addition to its carbon neutral potential. As with other unconventional technologies, its ability to produce natural gas will depend on our understanding of the processes and our ability to exploit this understanding. The approach taken during this project will be to understand the kinetic mechanisms that control the exchange of hydrate formers using numerical simulation to interpret field-scale trials, laboratory experiments to determine kinetic parameters, and code comparison to verify mathematical models and solution schemes.
Pacific Northwest National Laboratory (PNNL), Richland, WA
The numerical simulation component of the project involves the development and application of the computer code STOMP-HYDT-KE to investigate the production of geologic accumulations of natural gas hydrates via depressurization, thermal stimulation, inhibitor injection, or guest-molecule swapping. The STOMP-HYDT-KE computer code solves conservation equations for energy; water mass; mobile N2, CO2, and CH4; clathrated N2, CO2, and CH4; and salt or inhibitor mass. Solving conservation equations for both mobile and clathrated hydrate formers (i.e., N2, CO2, and CH4) allows the code to mode swapping process as being kinetic. Whereas systems of interest have been generally limited to those involving aqueous-gas-hydrate phases, STOMP-HYDT-KE additionally considers nonaqueous liquid, ice, and precipitated salt phases. The STOMP-HYDT-KE also has capabilities for solving coupled geochemistry problems via its ECKEChem module, giving the code thermal-hydrological-geochemical (THC) capabilities. An element of the project will be to extend these capabilities to include integrated geomechanical capabilities, allowing the simulator to model changes in the geomechanical state of the hydrate bearing reservoir throughout the production process.
Important issues regarding reservoir stimulation techniques, safety, and cost must be addressed before large-scale commercial recovery of natural gas from hydrates can be attempted. Reservoir modeling is an important tool for addressing these issues; however, applying this modeling tool requires access to reliable thermodynamic, kinetic, and physical property data for gas hydrates and physicochemical properties of the hydrate-bearing sediments themselves. Laboratory studies to characterize gas chemistries of synthetic gas hydrate sands have been conducted using a residual gas analyzer. The proposed experiments will leverage the results of previous experiments where the gas composition within a synthetically rich methane hydrate core was successfully monitored, allowing the use of acquired hydrate dissociation kinetics. Furthermore, proposed measurements using the pressurized x-ray diffraction technique are unique and will be some of the first reported. This technique was successfully used to track mineral dissolution, carbonation reactions, and mineral volume changes. The types of structural information gained from this technique are believed to improve fundamental understanding of mechanisms that occur during the gas swapping process.
The conventional technologies for producing natural gas hydrates from geologic repositories—especially those with pore-filling type hydrates—are reasonably well understood, and numerical simulations have been compared against field trials. In contrast, the guest-molecule-exchange approach for natural gas hydrate production is emerging unconventional technology. This project will aid in the interpretation of data collected from the 2012 Iġnik Sikumi gas hydrate field trial. The ultimate objective of this research is to develop numerical simulation tools capable of predicting the performance of the guest-molecule-exchange technology at the reservoir scale, including the geomechanical stability of the process. The work represents a first step in validating a numerical simulator capable of modeling the kinetic exchange of hydrate guest molecules. A credible interpretation of the Iġnik Sikumi gas hydrate field trial, realized through numerical simulation, will greatly increase understanding of the fundamental exchange processes for hydrate formers.
Support from U.S. DOE/NETL and KIGAM have yielded simulation capabilities in the STOMP-HYDT-KE simulator that allow for the modeling of fully coupled multifluid hydrologic, heat transfer, hydrate thermodynamics, and geochemistry. Moreover, the simulator is formulated to model the exchange of hydrate formers, hydrate dissociation, and hydrate formation as kinetic processes for a ternary hydrate former system N2, CO2, and CH4. The missing element in this suite of capabilities is the coupling with geomechanics; where, changes in pore pressure and temperature yield changes in effective stress, resulting in rock deformation or failure. These deformations or changes in stresses in turn yield changes in porosity and intrinsic permeability, which directly impact the hydrologic system. The proposed work will allow for the coupling to be integrated into a single simulator with capabilities for execution on sequential, shared-memory parallel, and distributed-memory parallel computers. Kinetic hydrate simulations are computationally expensive and coupling geomechanics adds to that expense, which makes parallel computing a necessity to realize problem solutions to real-world problems at reservoir scales.
The goal of this experimental work is to conduct measurements of methane hydrate dissociation and structural stability in hydrate‐bearing sediments using a high-pressure cell and state-of-the-art analytical techniques. The kinetic exchange rates obtained on the ternary gas system will be utilized to validate numerical codes, and the structural data will further support the concept of continuous stability of gas hydrate structures during gas swapping.
The STOMP-HYDT-KE computer code is a reservoir-scale numerical simulator with both sequential and parallel implementations. STOMP-HYDT-KE has been applied against the 2012 Iġnik Sikumi #1 gas hydrate field trial, and against a series of flow-through CH4 replacement experiments. During the flow-through experiments, kinetic rate parameters were determined via inverse modeling against the experimental observations.
A series of guest-molecule exchange experiments have been conducted involving the replacement of mixtures of N2 and CO2 with clathrated CH4 under different temperature and pressure conditions. The target pressure and temperature conditions varied between being within and outside the stability zone for the N2 and CO2 mixture, but always within the stability zone for pure CH4 hydrate. The first study targeted under this task was the development of a standardized procedure to perform in situ monitoring of pore gas chemistry during the replacement of methane in a CH4 hydrate bearing porous sand with CO2 through the titration of a gaseous mixtures consisting of different ratios of N2/CO2. The continuous monitoring of pore gas chemistry would provide clear evidence of the rates associated with the exchange of CH4 with CO2. The goal of these experiments was to develop kinetic exchange rates and parameters for use in the simulations conducted under the Iġnik Sikumi History Match task.
Current Status (November 2016)
PNNL is developing a geomechanical module that will be implemented into the STOMP-HYDT-KE simulator in a coupled, sequential scheme. When implemented, coupled heat transfer, multifluid flow, and kinetic exchange of hydrate formers will be solved. The reactive transport module, ECKEChem, will be executed if geochemical reactions are required in the simulation scenario. Following the geochemical calculations, the geomechanical calculations will be executed, driven by changes in pressure and temperature computed from the coupled THC solution. The geomechanical module will yield stress, strain, and deformation.
Project Start: June 1, 2013
Project End: September 30, 2018
Project Cost Information:
All DOE Funding
FY13 DOE Share: $90,000
FY14 DOE Share: $80,000
FY15 – DOE Share - $50,000
Total Funding to Date: $220,000
NETL – Adam Tew (firstname.lastname@example.org or 412-386-5389)
PNNL – Mark White (email@example.com or 509-372-6070)
Quarterly Research Progress Report [PDF-315KB] October - December, 2014
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Quarterly Research Progress Report [PDF-418KB] October - December, 2013
Quarterly Research Progress Report [PDF-210KB] July - September, 2013