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CLIMIT-Forskning, utvikling og demo av CO2-håndtering

Improved performance of CO2 EOR and underground storage by mobility control of CO2

Alternative title: Mobilitetskontroll av CO2 for forbedret utnyttelse ved EOR og akviferlagring

Awarded: NOK 8.9 mill.

Underground storage is a large-scale solution for reducing anthropogenic emissions of CO2.The storage capacity in the North Sea formations is large and the possibility for establishing a large-scale infrastructure for CO2 storage have been evaluated. The realisation of a CO2 infrastructure will make CO2 available for EOR. To obtain a good macroscopic sweep is a challenge for CO2 based EOR. The same can be the case for aquifer storage if water must be produced to limit build-up of pressure and to increase the storage capacity. The main objective of the project was to develop technology that can reduce the mobility of CO2. As secondary objectives, various means of controlling the mobility of CO2 have been identified and evaluated. Improved sweep can improve the economy both during CO2 EOR and aquifer storage provided that suitable additives can be identified and that the cost of using the additives is less compared to the technical improvement. The additives must also be environmentally acceptable. The mobility of gas can to some extent be controlled by foam formed by use of water-soluble surfactants. However, such surfactants have a limitation as the flow of gas and the surfactant solution may separate some distance from the injection wells and foam can no more be formed. With a CO2-soluble surfactant foam can be formed wherever CO2 and water co-exists. This can offer a new tool for mobility control. The use of CO2-soluble surfactants has been focused in the present project. The use of water-soluble surfactants and nanoparticles, either as direct thickeners of CO2 or as dispersants have also been addressed for CO2 EOR. Numerical reservoir simulations with realistic models and relevant input data for the main physical phenomena involved are needed to evaluate the effect of additives for mobility control. Simplified reservoir simulations for aquifer storage using a commercial reservoir simulator and different reservoir geometries show that improved sweep efficiency by foam can increase the storage capacity by a factor of three compared to the base case without foam. High pressure in the injection well can be a problem if to strong foam is formed. Improved simulation tools that can include effects such as rate dependent properties of foam, surfactant partitioning between CO2 and water, concentration effects and adsorption/desorption will be needed both for more accurate simulations and for defining desired surfactant properties. A simulation tool that includes these functionalities is developed on the simulator platform MRST through the task "Reservoir management and EOR" within the Norwegian CCS Research Centre, NCCS. Further development and testing of the simulator is needed. A series of foam injection flooding experiments that enabled the determination of CO2 and water relative permeabilities were done previously. Various surfactants were used. CO2 injection experiments in a 1.15 m long Bentheimer core saturated with surfactant solution have been done using the same surfactants. All non-ionic surfactants were ethoxylates, but with different structures on the hydrophobic part. The results showed larger variations in behaviour compared to the previous experiments. Some of the difference can be explained by different solubilities of the surfactants in CO2. The non-ionic surfactants appear to form foam easier at low injection rates compared to the anionic surfactant included as a reference. The results from the experiments are used to test the MRST foam model. Long core experiments with oil have shown that the three tested surfactants formed stable foams in the presence of a reservoir from a Norwegian oil field. Surfactant partitioning experiments show that the distribution of surfactant between brine and CO2 varies significantly depending on the structure of the surfactant, pressure, temperature and concentration. A unique "oscillating drop" rheometer has been developed in co-operation with the German company DataPhysics Instruments GmbH. This instrument enables the measurement of surface viscosity and surface elasticity of foam lamellae at high temperature and high pressure. Measurements using the same surfactant systems as used in the core flooding experiments show that it has not been possible to relate measured surface rheology to foam properties in porous media. Only a limited number of surfactants have been tested, however. Surface rheology is often important for the behaviour of processes with dispersed fluids.

Resultater fra prosjektet har vist at det er mulig å danne stabile skum mellom CO2 og tensidløsninger ved betingelser som er relevante for CO2 EOR og akviferlagring av CO2. Alle de utprøvde tensidene, både et anionisk referanse tensid og et lite utvalg av ikke-ioniske tensid dannet skum, men egenskapene avhenger av type tensid. Transport av skum i porøse materialer er en kompleks prosess. For å kunne predikere en feltskala skuminjeksjon og identifisere ønskede tensidegenskaper er det nødvendig med en simulator som kan bergene virkningen av skum. Arbeidet med å utvikle en skumsimulator pågår i et parallelt prosjekt med data fra det pågående prosjekt. Gjennom prosjektarbeidet er det tatt i bruk og utviklet en rekke laboratorieteknikker for måling av skumegenskaper. Sammen med et fysikalsk basert simuleringsverktøy gir dette et godt grunnlag for videre arbeid relatert til mobilitetskontroll ved injeksjon av CO2 der skum ser ut til å være den best egnede metode.

Most water flooded North Sea reservoirs are becoming mature with increasing water cuts. The need for effective methods to mobilise some of the remaining resources is therefore urgent. CO2 EOR in large scale is an interesting option. However, due to the offshore location the well spacing is large and the need to control the mobility is therefore important in order to achieve good macroscopic sweep. CO2 storage in sedimentary rocks has been recognized as a solution for reducing the emission of CO2. The storage capacity in the North Sea formations may be sufficient for EU point sources for the fossil era. Plans for establishing a large scale infrastructure is presently being evaluated. The realisation of a CO2 infrastructure will make CO2 available for EOR. In this project various means for controlling the mobility of CO2 at conditions relevant for CO2 based EOR and aquifer storage in Norwegian continental shelf formations will be identified and evaluated. In the first part of the project a state of the art literature review for different methods for CO2 mobility control will be performed. This includes traditional foams based on surfactants solubilised in brine, foams using surfactants solubilised in CO2, foams stabilised by nanoparticles, components added as direct CO2 thickeners and nanoparticles used as CO2 thickeners. The review will be supported by simplified reservoir simulations. In the following parts of the project the use of water and CO2 soluble surfactants and various types of nanoparticles will be studied experimentally. This will include both bulk phase and core flooding experiments, numerical simulations and simplified economic evaluations. The priority of topics may be changed depending on the outcome of the first part. The project will adress novel techniques for mobility control and a post.doc. position will be included in the work. The project will be done in cooperation with North American universities.

Funding scheme:

CLIMIT-Forskning, utvikling og demo av CO2-håndtering