Abstract
In the transition to a sustainable energy system, natural gas may be an interim source for relatively low-carbon energy production. However, hydrocarbon production worldwide is leading to reservoir compaction and, consequently, surface subsidence and induced seismicity, hampering the potential of natural gas. Reservoir compaction may potentially be mitigated by fluid injection. Fluid injection into porous subsurface reservoirs is also required in other technologies envisioned in a sustainable energy system, such as geothermal energy production and temporary storage of renewable energy. However, fluid injection into porous reservoirs may create a chemical disequilibrium between the pore fluid and host rock, potentially activating fluid–rock interactions that can cause compaction of the reservoir. These chemically activated fluid–rock interactions are not well-understood, and, therefore, we performed uniaxial compaction experiments at 35, 75 and 100 MPa effective stress, employing samples of Bentheim sandstone saturated with supercritical phases (i.e. N2, CO2, wet-N2 and wet-CO2), distilled water and aqueous solutions (i.e. 3.7 pH HCl solution, AMP solution and AlCl3 solution), as well as low-vacuum (dry) conditions. Creep strain and acoustic emissions (AEs) accumulated with increasing stress and sample porosity. While saturation with supercritical fluids produced slightly less creep strain than dry conditions, flooding with distilled water doubled the creep strain. The acidic solutions inhibited compaction creep compared to distilled water saturation. AE activity and microstructural analysis revealed that microcracking controlled deformation, presumably via stress corrosion cracking. While the supercritical fluids may have dried crack tips, distilled water likely reduced the stress required for Si-O bond breakage. The acidic solutions inhibited microcracking through, presumably, a change in surface energy. Our results suggest that fluids devoid of water, with low water content or acidic in nature can be injected into quartz-rich porous reservoirs without increasing reservoir compaction rates.
Highlights
Natural gas is expected to play an important interim role during the transition from fossil fuels to sustainable energy as a lower carbon alternative to coal and oil.[1]
Together with (a) the acoustic emissions (AEs) activity observed during creep (Figs. 4, 6 and 7), (b) the linear relation observed between AE rate and strain rate, which was characterised by a slope of 1 (Fig. 5b), and (c) microstructural analysis, which showed an abundance of new cracks in the quartz grains post-creep deformation, it is inferred that compaction creep was accommodated by microcracking in quartz grains and breakage of cemented grain contacts with serial rearrangement of grains and grain fragments
The results presented in this study may have several implications regarding fluid injection into porous subsurface reservoirs at 2–4 km depth, where microcracking is likely to contribute to reservoir deformation, when stress conditions are perturbed to provide a drive for compaction creep
Summary
Natural gas is expected to play an important interim role during the transition from fossil fuels to sustainable energy as a lower carbon alternative to coal and oil.[1]. Subsurface fluid injection into aquifers and depleted hydrocarbon reservoirs plays an important role in other strategies to reduce carbon emissions, notably in the context of geothermal electricity generation and geothermal heating of homes and building infrastructure.[1,9] In addition, depleted hydrocarbon reservoirs are targeted for permanent disposal of wastewater[10] and CO2, and for temporary storage of renewable energy[11] in the form of synthetic fuels,[12] compressed air,[13] or hydrogen.[14]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
