Study Investigates Hydrogen Storage in Depleted Shale Reservoirs
Authors: Carpenter Chris 
Published: January 2024

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 213851, “Effect of Hydrogen Interaction With Crude Oil on the Extraction of Hydrogen if Stored in Depleted Shale Reservoirs: An Experimental Study Analyzing the Outcome of Cyclic Hydrogen Injection Into Oil-Saturated Core Samples,” by Elie Bechara, SPE, Talal Gamadi, and Aboubakar Mahamadene, Texas Tech University, et al. The paper has not been peer reviewed.

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One of the main challenges of underground hydrogen storage in porous media (UHSP) is ensuring efficient hydrogen extraction after long storage periods. If the possibility of efficient UHSP in depleted oil-producing shale reservoirs is to be explored, it should be ascertained whether hydrogen interaction with residual oil throughout the storage period leads to recovering undesirable amounts of oil during hydrogen extraction. The study detailed in the complete paper adds to the ongoing research in hydrogen storage, focusing on efficient extraction of hydrogen to be stored potentially in depleted unconventional formations.

Materials and Methods
Core-Sample Preparation. Cylindrical core samples were prepared with a 1.5-in. diameter and a 3-in. length. The two used samples, Bk5 and Bk6, originated from the Bakken formation and were extracted at a depth exceeding 11,000 ft. Samples were dried by oven heating until a minimal difference in weight was recorded after 24 hours of heating. On average, it took approximately 3 days for a sample to dry at 230°F. The final dry weight of the core sample was recorded. A core was then kept well-insulated until further experimental work was conducted.
Porosity Measurement. A helium gas expansion porosimeter was used to measure the grain volume, porous volume, and effective porosity of the two core samples. Pore pressure and confining pressure were set at 200 and 700 psi, respectively.
Oil Saturation of Core Samples. The crude oil used in the experiments featured a density of 0.765g/cm3 and a viscosity of 3.15 cp. The saturation setup was built using a high-pressure core holder, a vacuum pump, a Quizix pump, a distilled water supply, and a floating piston accumulator. The core samples were assumed to be dry and not saturated with any type of fluid before saturation. The dry core samples were initially vacuumed for 3 consecutive days to ameliorate the oil-saturation process. The accumulator was filled with crude oil, with the floating piston at the bottom of the accumulator. Distilled water was pumped into the accumulator by the Quizix pump, displacing the piston in the process and supplying crude oil to the core holder at a pressure of 1,200 psi. The samples were weighed three times before and after the saturation process. Oil was assumed to be the only fluid occupying the pore space throughout the experimental work. Accordingly, the weight increase caused by saturation was divided by the oil density to estimate the sample’s oil volume. This oil volume was then divided by the porous volume to deduce the sample’s oil saturation. The saturation setup was pressurized at 1,200 psi using the Quizix pump. The sample was weighed every 30 minutes until the desired oil saturation was achieved. One sample (Bk5) was saturated at approximately 60% (achieved 59.27%) and another (Bk6) at approximately 40% (achieved 40.07%).