Leakage From Coexisting Geologic Forcing and Injection‐Induced Pressurization: A Semi‐Analytical Solution for Multilayered Aquifers With Multiple Wells. Issue 5 (6th May 2022)

• Record Type: Journal Article
• Authors: Cihan, A.; Oldenburg, C. M.; Birkholzer, J. T.
• Is Part Of: Water resources research. Volume 58:Issue 5(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-05-06
• Subjects: brine leakage -- pre‐injection overpressure -- semi‐analytical model -- abandoned wells -- geological carbon sequestration; Hydrology -- Periodicals; 333.91
• DOI: 10.1029/2022WR032343
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: Abnormal fluid pressures (above or below hydrostatic pressure) can develop and persist in sedimentary basins. The common occurrence of abnormal pressures may cause challenges for project permitting of geological carbon sequestration (GCS), particularly in reservoirs with pre‐injection overpressure. The leaky wells that may exist in some sedimentary basins can provide flow paths between deep brine aquifers and shallower freshwater aquifers. Pre‐injection relative overpressures can cause brine leakage through leaky wells even before any injection occurs. The tendency for flow through leaky wells is coupled with the process of pressure dissipation that occurs through aquitards. Specifically, with non‐zero permeability, aquitards can dissipate pressure over large areal extents and thereby reduce leakage rates through leaky wells. This study presents development of a semi‐analytical solution for hydraulic head and brine leakage in multilayered aquifer–aquitard systems with geologic pressure forcing. The geologic forcing that causes abnormal pressures in the multilayered system can coexist with any number of injection, extraction, and leaky wells that also affect fluid pressure. The semi‐analytical model is applied to explore how leakage through leaky wells varies as functions of pressurization rate, along with aquitard and leaky well properties in an overpressured multilayered system. The results show that although injection‐induced pressures can dissipate rapidly through suitably permeable aquitards, coexisting geologic forcing may create sustained rates of brine leakage into freshwater aquifers through leaky wells. In GCS, a very low‐permeability aquitard with high capillary entry pressure to free‐phase CO2 is desired to serve as the caprock to prevent leakage of CO2 from the storage reservoir. Nevertheless, the results from this study show that the brine leakage impact to shallow freshwater aquifers through leaky wells might substantially decrease with increasing aquitard permeability values, as long as small aquitard permeability and high capillary entry pressure serve to prevent CO2 leakage. Key Points: This study extends semi‐analytical solutions for leakage in abnormally pressured multilayered aquifer systems undergoing fluid injection New solution presented predicts brine leakage from leaky wells caused by coexisting geologic forcing and injection Although the injection‐induced pressures may dissipate through permeable aquitards, coexisting geologic forcing may add to the manmade forcing to create sustained brine leakage rates into aquifers through leaky wells