Abstract
Reservoir formation waters typically contain scaling ions which can precipitate and form mineral deposits. Such mineral deposition can be accelerated electrochemically, whereby the application of potential between two electrodes results in oxygen reduction and water electrolysis. Both processes change the local pH near the electrodes and affect the surface deposition of pH-sensitive minerals. In the context of the plugging and abandonment of wells, electrochemically enhanced deposition could offer a cost-effective alternative to the established methods that rely on setting cement plugs. In this paper, we tested the scale electro-deposition ability of six different formation waters from selected reservoirs along the Norwegian continental shelf using two experimental setups, one containing CO2 and one without CO2. As the electrochemical deposition of scaling minerals relies on local pH changes near the cathode, geochemical modelling was performed to predict oversaturation with respect to the different mineral phases at different pH values. In a CO2-free environment, the formation waters are mainly oversaturated with portlandite at pH > 12. When CO2 was introduced to the system, the formation waters were oversaturated with calcite. The presence of mineral phases was confirmed by powder X-ray diffraction (XRD) analyses of the mineral deposits obtained in the laboratory experiments. The geochemical-modelling results indicate several oversaturated Mg-bearing minerals (e.g., brucite, dolomite, aragonite) in the formation waters but these, according to XRD results, were absent in the deposits, which is likely due to the significant domination of calcium-scaling ions in the solution. The amount of deposit was found to be proportional to the concentration of calcium present in the formation waters. Formation waters with a high concentration of Ca ions and a high conductivity yielded more precipitate.
Highlights
Publisher’s Note: MDPI stays neutralThe exploration of the Earth’s interior has been pursued by mankind for millennia: from drilling small wells to access fresh water, to making large well structures to extract energy
The highest conductivity was encountered in the Gyda brine while the lowest was in Statfjord, which is in line with the amount of the electrolyte present in the solution (Table 1) [33]
The conductivity of the Troll and Statfjord formation waters is in the range of distilled water [34], meaning they will still conduct electric current, but the concentration of ions is not high enough for water splitting to occur to any great extent [33]
Summary
Publisher’s Note: MDPI stays neutralThe exploration of the Earth’s interior has been pursued by mankind for millennia: from drilling small wells to access fresh water, to making large well structures to extract energy. Wells allow us to gather scientific data from deep inside the Earth, produce oil or gas, inject gases into reservoirs for long- or short-term storage, extract geothermal energy and bury nuclear waste and other contaminants. The P&A procedures typically involve the removal of long sections of steel pipes, placing a number of cement plugs in the wellbore and the restoration of annular barriers in the well [3,4,5,6]. These operations are huge cost drivers due to the need for expensive drilling rigs and equipment [6]. In the North Sea, up to £3 billion with regard to jurisdictional claims in published maps and institutional affiliations
Sign-in/Register to view highlights & summary 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 callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
