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Improved oil recovery using polymer flooding techniques

Polymer flooding is emerging as a technique for improved oil recovery (IOR) with significant potential. It is expected to become the most widely applied IOR technique in Europe. Any polymers to be considered for use need to suit the conditions of the reservoirs where they are expected to function. For example, oil bearing reservoirs in the North Sea and Central Europe have high salinity and temperatures up to 90 C. A novel bio-polymer, Xanthan, has been investigated and characterized to assess its suitability for use in North Sea and Central European reservoirs. Xanthan has properties that make it appropriate for use in improved recovery compared with other polymers used at present. These properties include its rheological behaviour and its high stability at elevated temperatures and high concentrations of brine.

Xanthan was used in heterogeneous reservoirs to quantify IOR capacity. The stability of Xanthan was investigated under high temperatures and strong saline concentrations to mimic the North Sea and Central European environments. The rheology of Xanthan solutions and its capacity to displace crude from porous mediums was assessed. Several aspects of the interaction of the Xanthan solutions with the medium walls were investigated. These studies included investigation into the effects of micro-heterogeneities of the porous media on oil recovery by polymer flooding. The transport mechanisms of macromolecules in porous media were also assessed with and without oil present. A mathematical model of the polymer's behaviour was developed that incorporated results from basic flow experiments with sand packs and sandstone cores. Further modelling of displacement in heterogeneous media was also carried out using geostatistical methods currently in use for reservoir characterization.

The results showed that Xanthan may be a suitable polymer for application under the adverse temperature and salinity conditions experienced in these heterogeneous reservoirs.

The basic scientific knowledge regarding the behaviour of Xanthan has been improved. Results included flow experiments of Xanthan solution in porous media and in tubes. These compiled details of the interactions of the polymer molecules with the pore wall and the effective permeability of the polymer solution. The thermal stability of Xanthan material used was found to be limited to about 70 C. Thermal degradation of Xanthan was accelerated in the presence of sand, whilst additives such as thiourea and sodium pyruvate were effective as thermal stabilizers. The results provided more information on the flow behaviour of the macromolecules in the pore space, especially at the oil/aqueous phase interface and displacement from behind the oil/aqueous phase.

A thorough understanding of the opportunities for use of the polymer Xanthan will, in time, lead to a greater uptake in IOR. At present, low oil prices do not encourage expenditure on high amounts of IOR, but in future it will be of value when oil prices rise.

Contacto

Dagobert KESSEL
Tel.: +49-5323-7110
Fax: +49-5323-711200
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