Published by the DTI Oil & Gas Directorate for the reservoir engineering and IOR community in the UK.
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CO2 Miscibility Properties for North Sea IOR

Claire Woods of AEA Technology describes a JIP proposal to provide the industry with data and tools to assess the benefits of CO2 injection in the North Sea. (The proposal was submitted to the Advisory Committee on Hydrocarbons Additional Recovery Research, April 2002) (claire.woods@aeat.co.uk)

It is generally accepted that increasing concentrations of CO2 in the atmosphere are contributing to global warming and climate change. The UK government has announced a national target of a 20% reduction in CO2 emissions by 2010. Capture and storage (sequestration) of CO2 may be necessary, in conjunction with other abatement techniques, to achieve this target. CO2 injection has been used successfully as an IOR technique in onshore fields, mainly in the Permian Basin, for over 20 years, but it has yet to be adopted in the offshore environment. Fiscal, legislative or environmental incentives for sequestration might provide the impetus to overcome this hurdle.

The IOR from a WAG project can depend critically on the degree of miscibility between the injected gas and the oil, and the operating conditions in onshore USA and North Sea fields differ significantly.

Operating Conditions for North American and UKCS Fields

There are two methods of predicting CO2 miscibility. The first utilises empirical correlations based on the oil composition and temperature. The second uses equations of state (EoS) to model the component transfer between phases. Existing correlations are based mainly on North American onshore data and predictions differ significantly when applied to North Sea fluids. There are no published measurements for North Sea fluids with which to test or verify the correlations. In addition, recent studies by AEA Technology have shown that uncertainties in the EoS parameters can affect the predictions significantly.

As neither method of estimating miscibility is reliable, it is possible that CO2 injection may be incorrectly ruled out during studies of development options. The aim of this project is to provide the industry with North Sea data and improved CO2 miscibility prediction tools to enable them to assess the benefits of CO2 gas injection for particular field developments.

It is envisaged that 8-10 North Sea oils could be studied in this joint industry project. This should provide sufficient data for the development of correlations and equations of state for CO2 flooding of North Sea fields at an affordable cost, and provide data directly relevant to each individual company's field development plans. This project has been designed to extract value from the experimental data and provide sponsors with the improved tools necessary to fully realise opportunities created by the potential availability of large quantities of cheap CO2 for sequestration. The new correlations and equations of state will be used in simulations of CO2 floods in a reservoir scenario representative of a candidate field, to give an indication of field-scale issues not observed in the laboratory studies.

Flow Chart of Work Packages

The project is planned to start in early 2003 and run for 2 years. Deliverables include:

• An improved method for determining CO2 binary interaction coefficients appropriate to CO2 miscible injection
• An improved correlation for the prediction of CO2 MMP for North Sea fluids
• A validated database of CO2 MMP data
• A better understanding of issues affecting CO2 miscibility
• Simulations applying the laboratory data and their interpretation to a typical field-scale CO2 miscible flooding project.
  

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