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CLIMIT-Forskning, utvikling og demo av CO2-håndtering

Preventing loss of near-well permeability in CO2 injection wells

Alternative title: Hindre redusert nærbrønnspermeabilitet i CO2-injeksjonsbrønner

Awarded: NOK 9.0 mill.

CO2 storage projects involve the pumping CO2 from injection wells into porous underground rock formations. An important prerequisite is that the injection can be done in a safe and efficient manner, and this requires sufficient flow of CO2 from the well into the formation. CO2 injection has shown to be challenging in several cases, since there are many potential mechanisms than can lead to clogging of the near wellbore area. In this project, we have chosen to study some of the clogging mechanisms from an operational perspective; that is, we will try to understand how the conditions in the near wellbore area, such as stresses, pressure, temperature, flow, and rock type, as well as stops and starts in CO2 injection, influence the risk of clogging. This could be caused by e.g. salt precipitation, wax or hydrate formation, bacterial films, clay swelling, and transport of fines from partially crushed rock around the well. Small scale flow experiments will be performed to study fundamental clogging mechanisms. Medium scale injection experiments will be done on rock specimens formed as downscaled injection wells using a specially designed true triaxial instrument capable of replicating the unique stress, pressure, temperature and injection patterns of a real injection well. The results will be implemented in a simulator tool for planning and operation of CO2 injection wells. The project was initiated in 2018 with a kick-off meeting in Trondheim, and a follow-up workshop in Stavanger. The consortium steering committee usually meets thrice a year, with additional digital status or technical meetings, although all meetings in 2020 have been digital. We have studied how rock type and flow direction, and gravity/bouyancy affect precipitation and permeability changes as a part of understanding how these will be affected in the near well area, where the flow direction will change with distance from the well. Different flow rates are studied to complete this picture. Experiments with radial flow in downscaled wellbores are underway. A framework for stochastic modelling and upscaling is developet for interaction between CO2, water and rock. A solver for a two dimensional Lattice Boltzmann reactive transport model is developed in order to simulate dissolution and precipitation along fractures. A thermodynamic model based on PC-SAFT is further developed for hydrocarbon mixes and implemented in MRST as a separate module (open source). The development of a model for nucleation and growth of salt crystals has been initiated, and the goal is to understand how nucleation and growth affects the permeability in various rocks. This activity is supported by imaging of permeable rocks that have seen CO2 flow and precipitation. Transport modelling has started by developing a model in MRST that includes kinetics (time dependent equilibrium), that better replicates experimental findings in core flooding experiments. In the last period we have imaged small diameter cores accurately using micro CT to prepare for pore scale description of salt precipitation.

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This project aims to study how a high permeability in the near-well region can be maintained during intermittent CO2 injection and backflow of CO2-brine. Linear- and core-scale experiments will be performed to pinpoint the most relevant injectivity loss mechanisms at realistic field conditions, and unique radial flow experiments will thereafter be performed in a true triaxial test cell. This enables studies of not only precipitation reactions in pores (e.g. salt/wax formation), but also fines migration and loss of permeability due to grain displacement or shale swelling. Promising methods for injectivity loss mitigation (e.g. chemical injections) will also be tested. The experimental results will be used in a simulator to predict injectivity loss in the field, with a special test case related to the full-scale storage pilot at Smeaheia.

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CLIMIT-Forskning, utvikling og demo av CO2-håndtering