Electrode Placement Evaluation in Radio Frequency Hydrogen Generation Using Multiphysics Simulation
Authors: Ramsay Travis St. George 
Published: October 2022

The energy transition has steered the oil and gas industry's focus to reducing carbon intensity by way of tighter emissions controls and expediting the delivery of alternative clean energy solutions that address the burgeoning global energy demand. This has inevitably led to technology advances in the generation and production of clean hydrogen (H2) from petroleum reservoirs. As a part of these advances, the novel combination of technologies from disparate industries –such as energy and food processing industries, has occurred. These innovative technologies have broadened the use of multiphysics simulation tools in technology portfolios to move beyond classical applications in enhanced oil recovery (EOR) to now include clean hydrogen generation using in-situ radio frequency (RF) heating.

The following paper examines the usage of a previously developed dimensionless multiphysics Thermal-Phase Field-Mechanical-Electromagnetic (TPME) framework to model the generation of nearly CO2-free hydrogen from a petroleum reservoir considering in-situ radio frequency heating within the porous subsurface. Recent laboratory work has shown that the in-situ generation of nearly CO2-free hydrogen from petroleum reservoirs by radio frequency heating is possible via catalytic dehydration and that it would alleviate industrial carbon intensity by converting hydrocarbon reservoirs into hydrogen generators. An explicitly coupled TPME framework is used to simulate two-phase hydrogen generation from hydrocarbon by way of a Galerkin finite element method in a two-dimensional domain. Recently published work has demonstrated that the desired industrial carbon intensity reduction is achievable by hydrogen generation from converted petroleum reservoirs. As a corollary, it has been proposed that multiphysics simulation represents a key enabler in the assessment of in-situ hydrogen generation by radio frequency heating. Conversion performance is evaluated by considering geometric electrode placement in the simulated subsurface which describes hydrogen generation from hydrocarbon through an Allan-Cahn phase field.

Endothermic generation of hydrogen and phase interface tracking using the Allen-Cahn Phase Field method is achieved while examining the preferential orientation of electrodes within the modelled subsurface. The geological model was devised in a dimensionless simulation space with a comprehensive rock type description to better isolate the impact of radio frequency heating. Electrodes were placed vertically and horizontally within the computational domain to evaluate optimal placement methodologies. The results demonstrate that hydrogen generation occurs across the entirety of the target formation and the interpreted structural deformation is minimal leading to the suggestion that hydrogen generation by radio frequency heating is a mechanically stable process in the modelled environment. Overall, horizontal electrode placement was determined to be the preferred geometric orientation as construed by interface tracking across a series of experiments. Consequently, the slowest hydrogen generation times occurred with vertical electrode placement cases.