Reusing depleted oil and gas fields for CO2 sequestration - Norsk deltakelse

The RETURN project consortium, which was initiated by industry, consists of leading R&D providers in collaboration with several major oil and gas operator companies. The project focuses on unlocking the potential for CO2 storage in depleted oil and gas reservoirs. These sites are promising, as they are well characterized from previous oil and gas activities, and they have large pressure margins for safe storage. There are, however, some technical challenges related to storage in such sites. The low pressure in the depleted reservoirs results in strong cooling and potential freezing of the well and near-well region due to the Joule-Thomson effect and associated phase changes of the CO2. This jeopardizes not only injectivity, but also near-well stability and well integrity. Large depletion can be accompanied by strong stress concentration and hysteresis effect upon re-pressurisation, added to the development of thermal stress. Today's available solutions include heating of the CO2 and gas phase injection (dictating a high number of injectors). This is both expensive and emission-intensive. Novel solutions are thus required, which will be searched for and researched in the RETURN project, and which will ultimately enable safe and cost-efficient re-use of depleted reservoirs for long-term CO2 storage. The targeted research required to reach this goal is addressed in three main scientific work packages focusing on: (i) Coupled well-reservoir flow modelling, (ii) Near wellbore processes, and (iii) Wellbore integrity. The work, comprising both experiments, numerical modelling and larger scale field tests, will focus on understanding how CO2 flows down the well and into the depleted reservoir, and identifying safe operational windows both with respect to the near-well region and wellbores. The output of the project will be several scientific publications, as well as a handbook for industry with input for front-end engineering. Update: The installation of scientific fibreoptic cables at Svelvik CO2 Field Lab has been completed. Both straight and helical wound fibres are now accessible from the instrument cabin for all four monitoring wells and can be looped together as the operator wishes trough a connector panel. This equipment will be beneficial for the ACT SENSE project for leakage monitoring, and will be used in RETURN for checking models about CO2 plume propagation in the near-well area. One such test campaign was completed after the summer of 2023, where CO2 is injected into a well that we know is leaking, and fiber optics and geophones are used to look at the injection well and try to quantify the leak (we know the total volume injected, we know that we can accurately quantify the accumulated CO2 under the dense shale layer and we "cheat" by also measuring the leaked CO2 that comes up in the steel pipe that consolidates the well on the surface). In March 2023, the second annual meeting was held in Trondheim with participants physically present, as well as via video link. The second seminar for work package 5 was organized the following day at Rotvoll by Equinor. In June 2023, a joint seminar was held between RETURN and the EU project DISCO2 Store, at SINTEF in Trondheim, followed in September by a joint ACT 3 webinar (SHARP, Cementegrity and RETURN). Both events received a lot of attention and attracted committed participants. Other results at SINTEF have been mechanical, acoustic testing and CO2 exposure of small samples (Whitby and Lille John shale) in collaboration with NCCS. In addition, a low-frequency test has been run on Lille John, where a plug is "shaken" with tiny compression waves at a low, seismic frequency, which means that the stiffness of the material can be measured very accurately, before and after CO2 exposure. There seems to be no discernable stiffness change after exposure. Hydrate testing was also carried out in SINTEF, where CO2 is flowed through a plug while temperature and pressure are changed so that hydrate "ice" forms in the pores. Initial results show that the formation is not completely reversible when the temperature is increased again to the initial value.

Prosjektet RETURN har som hensikt å muliggjøre storskala lagring av CO2 i gamle olje og gassreservoarer, hvor trykket er veldig lavt etter mange år med produksjon av olje eller gass. RETURN samler mange industri og forskningspartnere i Norge, Nederland, Storbritannia, Tyskland, Italia og Canada. Det er stor gevinst i å lagre CO2 i uttømte felt, siden disse er velkjente fra produksjonstida og trykket er lavt, noe som tilsier at det er plass til store mengder CO2 uten lekkasjerisiko forbundet med for høyt trykk. Prosjektet vil håndtere tekniske utfordringer som gjenstår, knyttet til sterk kjøling av CO2 når det injiseres i lavtrykksreservoarer. Frysing, hydratdannelse og faseoverganger i nærbrønnsområdet kan føre til plugging av porenettverket og hindre videre injeksjon. Gode numeriske verktøy er nødvendig for å finne trygge driftsparametre. Videre må en ta hensyn til at spenningene i bergartformasjonene ikke endrer seg uniformt under produksjon av olje og gass. Ved injisering av CO2 kommer man ikke tilbake til den opprinnelige spenningsfordelingen. Spenningskonsentrasjoner kan dermed oppstå, med fare for oppsprekking og danning av en lekkasjevei. I tillegg må man håndtere spenninger som følge av temperaturendringer ved injeksjon av kald CO2. I dag håndterer man disse utfordringene ved å varme opp CO2 før injeksjon eller bruke et høyt antall brønner med lav rate. Løsningen er dyr og krever mye energi. RETURN vil forske på nye løsninger som har som mål å muliggjøre effektiv, billigere gjenbruk av tomme reservoarer for langtidsdeponering av CO2. For å nå målet blir det forsket på (i) nye strømningsmodeller som tar hensyn til koblingen mellom brønn og reservoar; (ii) oppførsel av bergarter under trykk og temperaturendringer og (iii) brønnintegritet under temperaturendringer, gjennom eksperimenter, modellering og felttesting. Prosjektet vil publisere resultatene og lage retningslinjer for industrien basert på reelle feltdata.