CEMENTEGRITY-prosjektet forsøker å utvikle og teste materialer som gir bedre tetting av brønnhull som er utsatt for CO2 lagret i underjordiske reservoarer. Slike materialer bør 1) forhindre at det dannes lekkasjer; 2) være selvreparerende dersom det likevel oppstår lekkasjer; 3) ha et mindre miljøfotavtrykk enn de materialene som brukes nå.
Lekkasje av CO2 gjennom eller langs brønnhull er en utfordring som må løses for å gi sikker lagring av CO2. Dagens materialer for tettning av brønnhull er vanligvis basert på Portlandsement, og integriteten til disse materialene kan være en sårbarhet under CO2-injeksjon og -lagring. Lekkasjer kan dannes gjennom sementen, eller langs grensesnittene mellom sement og stål eller sement og stein, som følge av kjemiske, termiske eller mekaniske effekter.
For å lykkes med å bedre tettningsmaterialer, må vi identifisere hvilke egenskaper som er kritiske for tetningens integritet. Vi må også utvikle praktiske metoder for å måle disse egenskapene under realistiske forhold, og modeller som kan brukes til ekstrapolering. CEMENTEGRITY prosjektet vil utføre eksperimentell forskning som tar for seg de kjemiske, termiske og mekaniske mekanismene som kan skade brønnboringens integritet under CO2-injeksjon og lagring. Vi vil teste en rekke forskjellige tettningsmaterialer. Vi vil støtte dette eksperimentelle arbeidet med numerisk modellering. Gjennom disse aktivitetene vil vi identifisere viktige egenskaper som sikrer langsiktig integritet av brønntetningsmaterialer, og vi vil også identifisere de best egnede metodene for måling av disse egenskapene. Våre funn kan deretter brukes når vi utvikler nye tettningsmaterialer for CO2-lagring, eller andre geologiske lagringskonsepter, for å sikre den langsiktige integriteten til underjordiske (CO2-)lagringsreservoarer.
CEMENTEGRITY performed experimental research studying five different sealant compositions, assessing their abilities to form and maintain a seal during hardening, to withstand exposure to CO2-containing fluids under in-situ conditions, and to maintain seal integrity when exposed to thermal shocks or cycles.
Doing so, we have delivered a deeper understanding of the potential mechanisms by which hydraulic sealants may be damaged and leakage pathways may form through or along seals during CO2-injection and -storage. But we have also identified what material properties in a hardened sealant may enhance its long-term ability to withstand such deleterious effects, and thus improve the likelihood seal integrity will be maintained.
This experimental research, combined with a review of relevant standards and guidelines on wellbore integrity, lead to the identification of critical properties for a sealant material. These properties should be measured when assessing a sealant material for a CCS application, and the impact on these properties of exposure to potentially deleterious conditions (for example to CO2 or thermal changes) should also be determined. This has been published openly.
Based on the key abilities and critical properties identified, Sealant Assessment Table was developed, that can support the development of novel sealants, or the assessment of sealant compositions for specific applications, and that is easily adapted to testing sealants for other geological storage applications, such as hydrogen-storage.
We have applied different methods for testing and exposing sealant samples, and to measure critical properties. These different methods and the outcomes were then compared, and a discussion was presented on what methods should be preferred, based on the research objectives and available resources – i.e., balancing complexity, duration, and cost with accuracy of results.
As part of our work, we have developed one geopolymer sealant (S5), and shown its suitability as a sealant during CCS. We developed a numerical model for the hardening of this geopolymer, and its subsequent exposure to CO2. We have also tested a new composition based on Portland Cement with a higher content of RePlug than hitherto used.
New methodologies in lab and field: 1. We have developed the use of micro-indentations to assess changes in mechanical properties resulting from exposure to CO2; 2. We have shown the potential to use electrical impedance measurements to study to monitor seal (interface) integrity in a well, though further development is needed.
Throughout, we have aimed to disseminate results not only academically, but also along different channels aimed in particular at engaging industry, and informing them about our progress. This was achieved in particular through open webinars (our Ceminars), a webinar for SPE, and through collaboration with ACT RETURN and SHARP. Industry partners were consulted regularly to ensure relevance of our findings.
The leakage of CO2 through or along wellbores has been identified as one of the main challenges to secure subsurface CO2-storage. Currently used wellbore sealants, commonly based on Ordinary Portland Cement, can be a large vulnerability during CO2-injection and -storage. Leakages may form through the cement, or along the cementsteel or cement-rock interfaces, as the result of chemical, thermal, or mechanical effects. Therefore, better sealants need to be developed that can prevent leakages from forming, and that demonstrate self-healing capabilities when leakage pathways do form. In order to successfully develop such materials, critical properties need to be identified that will ensure seal integrity, and practical methods and procedures for measuring these properties under in-situ conditions need to be developed, along with models for their extrapolation. CEMENTEGRITY will address the chemical, thermal and mechanical mechanisms that may damage wellbore integrity during CO2-injection and -storage, through experimental research on 5 different sealant compositions. WP1 will perform flow-through experiments with CO2 and CO2 bearing H2S to test changes in permeability and mechanical properties. WP2 will expose sealants to supercritical CO2 with H2S and other impurities, to investigate changes in composition. WP3 will expose sealant specimens to thermal shocks and cycling, to observe thermal cracking and annulusformation. WP4 will develop numerical models to extrapolate experimental results. WP5 will measure sealant-steel bond strengths, and develop electrical resistivity methods for in-situ monitoring of sealant and interface integrities. WP6 will develop a novel, rock-based geopolymer sealant specifically for CCS applications. Based on these WPs, WP7 will identify key properties to ensure long-term integrity of wellbore seals during CCS, as well as suitable methods for measuring these properties. These methods can then be applied when developing new sealants for CCS.
