Experimental Investigation of Wellbore Integrity of Depleted Oil and Gas Reservoirs for Underground Hydrogen Storage

Abstract

The is wide consensus that combustion of fossil fuels and rising greenhouse gas emissions in the atmosphere are accelerating global warming. To avoid the dilemma of need for fossil fuels to provide energy supply and the need to reduce fossil fuel related emissions, it is critical to promote renewable energy as a viable option to satisfy the world's energy requirements. However, employing renewables to generate power necessitates the use of bulk storage to accommodate discrepancies related to where and when renewable energy is produced versus where and when it is needed. Underground hydrogen storage has the potential to support establishment of hydrogen as a reliable source of clean energy across the planet. Where present, depleted oil and gas reservoirs, due to their existing infrastructure, can prove to be an attractive asset for underground hydrogen storage. One of the main challenges involved in the storage of hydrogen in the depleted oil and gas reservoirs is related to wellbore integrity. When hydrogen is injected or produced in the subsurface, it may get bin contact with cement around the wellbores. Hence it is necessary to investigate the effects of hydrogen interacting with the cement sheath. To study this in the laboratory, a core holder capable of simulating the wellbore conditions is used to conduct the tests. A 2" long, 1.5" diameter cement sample was placed inside the core holder and hydrogen was injected into it. Hydrogen was also injected into wet cement slurry to investigate possible stability of the cement samples. The effects of injecting hydrogen on set cement are studied using a CT Scanner which demonstrates if there is any formation of cracks and micro-annuli in the cement. The cement sample is crushed afterwards, and the presence of hydrogen particles in the structure of cement is evaluated by X -Ray Diffraction. A neat 15.5 lbs./gal Class "H" cement which is common in the industry is used in this study. Well integrity is a key success factor to establish the viability of underground hydrogen storage in the subsurface. For that we analyzed if the cement is good enough for hydrogen to be stored in depleted oil and gas reservoirs. We further studied the integrity of newly drilled wells when exposed to hydrogen.

Hydrogen Impact on Cement Integrity during Underground Hydrogen Storage: A Minireview and Future Outlook

“…It is recommended to examine the role of other associated factors, such as brine saturation, temperature, thermal conductivity, and pH, during hydrogen injection and production cycles. 49,52,65 Table 2 summarizes the main findings of recent laboratory and modeling studies on hydrogen/cement interactions.…”

“…Similarly, during H 2 injection, the possible degradation of cement integrity is not fully understood, and only limited studies have been performed. 25,49 Various factors can contribute to cement degradation during UHS, such as the presence of CO 2 in the brine/formation, 30 the generation of hydrogen sulfide, 50 and the existence of fractures in the cement sheath or microbial activities that lead to casing corrosion. 51 Therefore, addressing and understanding the associated issues of wellbore integrity during UHS are crucial for successful long-term containment/utilization of hydrogen as an energy source.…”

Storage Integrity during Underground Hydrogen Storage in Depleted Gas Reservoirs

“…Current study on cement degradation with hydrogen involved in still scarce. Hussain et al [153] tested the cement compressive strength and checked hydrogen bubbles within the cement by CT scanning after exposed to hydrogen and water at 120 o F and 1500 psi up to seven days using Class H cement. The results show that the compressive strength of cement decreases with increasing ageing time to hydrogen, implying that a certain redox-sensitive minerals (particularly hematite, Fe2O3) experienced reductive dissolution.…”

“…However, the presence of microbes can accelerate the reductive dissolution by providing extra electrons [5,81]. The reductive dissolution combined with the non-reductive dissolution of these minerals as either small fractions of cementation in sandstone reservoirs or higher fractions of compositional minerals in caprock can affect the in-situ petrophysical properties, such as increasing porosity and permeability [99], and weaken the rock by decreasing the compressive strength [153] thus impair the storage integrity.…”

“…Besides, as discussed in the section 3.2.2, the surrounding pH would increase when reservoirs contain sensitive minerals that can trigger redox reactions. Experimental and modelling data show that pH can increase to 9-12 in the presence of sensitive minerals during UHS [19,59,81,91,143,153]. As a result, it could be expected that the impact of microbial activities on biotic mineral dissolution/precipitation and associated storage integrity issues at high alkaline conditions is limited.…”