Modeling Hydrogen Storage in El Carito-Mulata and Santa Barbara Fields, Eastern Venezuela Basin: Focus on the Cushion Gas Effect and Identification of Recovery Mechanisms
Authors: Belhaj H. , Rodriguez F. , Askarova A. A. , Bejarano C. , Morales R. , AlDhuhoori M. , Alekhina T.V. , Dorhjie D. B. , Spivakova M. Y. , Mukhametova A. R. , Cheremisin A. N. , Enab K. 
Published: September 2024

Hydrogen storage in compositional reservoirs is often challenging and often a subject of keen interest to produce clean energy. For the case of El Carito-Mulata-Santa Barbara fields in Venezuela, reservoirs marked with variation from gas condensate to extra-heavy crude oil/tarmat, and local bodies of water and aquifers. Water and gas already injected for more than two decades and current reservoir pressure levels promote the formation of retrograde liquid/complex fluid mixtures and/or precipitation/deposition of asphaltene, it is essential to evaluate the effect of the type of gas injected to maintain reservoir pressure during hydrogen extraction.

The objective of this article is to predict, through numerical simulation, multitude of different hydrogen injection scenarios in El Carito-Mulata and Santa Barbara fields. The cushion gas effect, phase behavior, and identification of recovery mechanisms are also included. The fluid model of this study developed by tunning an Equation of State (EOS) to match PVT, swelling and coreflood tests. A developed scheme allowed the evaluation of the injection of H2, CH4, N2 and CO2. Because the available PVT tests do not report H2 as a single component, the properties of this component were taken from the literature. Displacement tests in composite cores and swelling tests with nitrogen and condensate gas maintained the evaluation of the effect of gas injection on fluid properties and hydrocarbon recovery. The main tunning parameters of the EOS were the critical properties of the heavy-end hydrocarbon fractions, volume shift and binary interaction coefficients in a consistent manner. Finally, the fluid model was used for the evaluation of the injection of different cushion gases, and predictions of injection and storage of hydrogen both in the upper part of the structure and in the water zones, using numerical simulation models.

This study introduces the main mechanisms present during the injection and storage of hydrogen (diffusivity, solubility, and hysteresis) in the selected fields using CH4, N2 and CO2 as cushion gases. The comparison between different scenarios of hydrogen storage and the impact on hydrogen production and additional hydrocarbon recovery discussed in this paper. The need for fluids sampling at current reservoir conditions emphasized in order to perform important laboratory tests (e.g., relative permeability tests, 3D pore-scale imagining, nuclear magnetic resonance corefloods, geochemical reactions, microbial tests, geomechanical tests, etc.). Hence, a better description and monitoring of the reservoir fluids, quantifying the initial and residual trapping of hydrogen, and assessing possible effect of pressure on the integrity of the reservoir achieved. This article presents an integrated workflow for the evaluation of hydrogen storage in reservoirs with complex fluid mixtures that serves as a basis for the feasibility studies and successful implementation of the process on a field scale.

The storage of hydrogen (H2) in subsurface reservoirs presents a promising solution for renewable energy storage. This study outlines a comprehensive workflow for evaluating hydrogen storage in reservoirs with complex fluid mixtures, considering various cushion gases (CH4, CO2, and N2). The methodology leverages existing Equations of State (EOS) tuning files and integrates hydrogen as a component in the modeling. This research provides insights into the mechanisms of hydrogen storage and production, offering a basis for feasibility studies and field-scale implementation.