Workflow Enables Technoeconomic Optimization of Underground Hydrogen Storage in Aquifers

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 220044, “Technoeconomic Optimization of Underground Hydrogen Storage in Aquifers,” by Behzad Amiri, SPE, Mojtaba Ghaedi, and Pål Østebø Andersen, SPE, University of Stavanger, et al. The paper has not been peer reviewed. _ Serious concerns exist about the economic feasibility of underground hydrogen (H2) storage (UHS) in aquifers. The authors’ objective is to investigate the use of an optimization workflow to maximize both H2 storage and net present value (NPV), consequently obtaining an optimal reservoir development strategy. Introduction An aquifer storage system for H2 typically consists of a brine-saturated formation layer, injection and withdrawal wells, and surface pipelines. The injected gas is divided into cushion gas (usually H2 or another gas) and working gas (H2). The main purpose of the cushion gas is to maintain sufficient minimum pressure, while the working gas is aimed at temporary storage and later production and sale. During UHS, the working gas is injected into the subsurface and then mixed with the formation fluid and extracted in a cyclical manner. Compressed H2 is injected into the target formation through a well. Fluid flow primarily is driven by pressure gradients and controlled by H2/brine mobility and density contrasts. However, the high mobility contrast between gas and water can lead to bypassing. Gravity segregation enhances the recovery of H2 during production but increases the risk of uncontrolled horizontal migration and leakage through the caprock. NPV analysis is used in UHS projects to assess if anticipated returns over time are sufficient to justify investment. By carefully formulating and optimizing the NPV, the profit of the storage process will be maximized. The complete paper details several works in the literature devoted to the economic potential and feasibility of hydrogen storage. To determine the profitability of the whole project, it is necessary to calculate the NPV. Furthermore, it is necessary to examine the interplay between H2-storage technical issues and NPV to determine the most effective development strategy. This research focuses on optimizing the development strategy of UHS in a deep aquifer. Methodology Aquifer Model. An open-source version of the Norne field model is used. The Norne field is on a raised block in the southern part of the Norwegian Sea. The Horst block has an estimated length of 9 km and a width of 3 km. The porosity of the material falls within the range of 25–30%, while the permeability varies from 20 to 2500 md. The original model consists of 22 vertical layers, which are further split into 46 and 112 grids in the x and y directions, respectively. The model consists of three separate zones: gas, oil, and water. An impermeable barrier, known as Not, separates the oil and water zones from the gas zone. The current research specifically examines the oil and water zones while excluding the gas zone from the model. The revised model is fully saturated with water by positioning the oil/water contact over the least-deep section of the reservoir. The eastern half of the model has been deactivated to improve computational efficiency. In its place, a pore volume multiplier of 30 is applied to the final vertical segment.