Tophole monitoring of permanently plugged wells

Mer enn 6300 brønner har så langt blitt boret på den norske kontinentalsokkelen, og rundt 200 nye forventes å bli boret hvert år framover. For å minimalisere miljøavtrykket er det viktig å forsikre seg om at brønnene forblir tette og ikke lekker ut hydrokarboner eller CO2 over tid. Utfordringen ligger først og fremst i brønnmaterialene som har begrenset levetid i de røffe forholdene nedihulls. Det er derfor viktig å samle informasjon om brønnenes tilstand for å undersøke om, når og hvor utbedring er nødvendig. Dette er spesielt utfordrende for brønner som har blitt permanent plugget og forlatt, siden øverste del har blitt kuttet og befinner seg flere meter under havbunnen. Hovedformålet med dette prosjektet er å utvikle en ny kostnadseffektiv metode for bestemmelse av brønnenes tilstand ved hjelp av fjernovervåking (slipper å bruke verktøy ned i brønnene). Dette vil være den første metoden i sin art, og det åpner flere muligheter for operatører og tjenesteleverandører: (i) kunnskap om sikkerhetsstatus for pluggede brønner over tid, (ii) tidlig identifisering av problembrønner og indikasjoner på hvor utbedring er nødvendig, (iii) informasjon om hvordan man kan forbedre fremtidig konstruksjon og plugging av brønner, (iv) sikrere og mer fleksibel gjenbruk av reservoarer for f.eks. CO2 lagring. Forskningen fokuserer på hvordan ulike signaltyper (f.eks. seismiske og elektromagnetiske) kan brukes til å gjenkjenne endringer i brønnen slik at dens tilstand over tid kan bestemmes. Prosjektet, ved hjelp av grunnleggende eksperimenter og simuleringer, baner vei for utvikling av ulike fjernmålingsprinsipper som kan anvendes på permanent pluggede brønner. Den bygger videre på eksisterende kunnskap om overvåkning av undergrunnen generelt og brønnenes tilstand mer spesifikt, og tar industrien fra en reaktiv tilstand (symptomdeteksjon) til en proaktiv tilstand (handling før lekkasje forekommer).

Results from the TOPHOLE project were published in three journal articles and seven conference proceedings, but also presented at conferences with 6 oral presentations and many poster contributions. The TOPHOLE researchers were conveners of the dedicated EAGE session "Legacy wells: threat and opportunities for energy and CO2 storage". Furthermore, TOPHOLE researcher were invited to present results at the NPD CO2 storage seminar, at University of Dublin, and at the IEAGHG Risk Management Network Meeting. More generally, we have carried out an impact assessment of the project, specifically targeting the main challenges for industrial development of CCS, i.e., risk reduction, cost reduction, and upscaling. Risk reduction is addressed by legacy well screening for containment risk assessment. It also provides input for evaluating the risk of migration out of the storage complex. Cost reduction aspects are addressed by adapting MMV plans accounting for the risks of legacy wells. The new technologies investigated in the project are also relevant for future wells to be plugged and abandonned. Finaly, the project impact is affecting the upscaling factor by unlocking the huge capacity for storage of the norwegian continental shelf including shutdown fields. It will also enhance public acceptance for CCS and energy storage. Parts of the TOPHOLE ideas were further implemented in the Green Platform project LINCCS (Linking large-scale, cost-effective, permanent offshore CO2 storage across the CCS value chain) which started 2021. TOPHOLE researchers were the main contributors to the CETP project LEGACY which is staring early 2024. TOPHOLE results together with TNO and SINTEF results from the ACT REXCO2 project has recently led to the establishment of the industry-funded software development project WISCOS (project start December 2023). Parts of the follow-up ideas from the TOPHOLE project were used to build the CHARISMA KSP-K project funded by CLIMIT in 2023.

The main objective of the project is to develop a novel cost-efficient method for tophole/non-invasive monitoring of permanently plugged wells that are cut below surface/seafloor. This will be the first method of its kind, and it opens several opportunities for operators and service providers: (i) knowledge of the safety status of plugged wells over time, (ii) early identification of problem wells and indications of where remediation is needed, (iii) information on how to improve well construction and plugging methods in the future, (iv) safer and more flexible re-use of reservoir space for e.g. CO2 storage. The research will focus on how various signal types (e.g., seismic and electromagnetic) can be utilized for remote well integrity evaluation and how anomaly detection can be used to pinpoint well integrity changes over time. The main research challenges are: (i) Determine the general sensitivities of different mechanical and electromagnetic wave-types and modes to changes in the well and its components (e.g., casing, cement, and their bonding), using lab experiments and numerical modelling for relevant signal frequencies. (ii) Investigate how the data that are sensitive to changes of well conditions can be created and measured at the surface or on the sea floor. (iii) Develop methods for the detection, identification, location, and quantification of anomalies in the well. (iv) Evaluate the findings for potential future smart well designs. The current project will, by fundamental experiments and simulations, pave the way for developing a remote non-invasive well integrity monitoring technique that is applicable also for P&A'ed wells. It will build on existing knowledge on subsurface- and well integrity monitoring, and will take the industry from a reactive state (symptom detection) to proactive state (take action before leakage occurs).