Water flooding is a commonly applied operation in many petroleum fields to increase oil production. The heterogeneities in the oil composition as well as in the reservoir are two main factors impeding the sweep efficiency of water flooding and causing unexpected field problems. The present study integrates geochemical characterization of oils collected before and after water flooding and production information of the studied field.

The oils are characterized by a number of geochemical parameters indicative for source rock type, maturity and mobility determined by GC and GC-MS. Prior to water flooding, the results suggest a uniform oil composition regarding the source and maturity of the oils within the reservoir. The oil produced from a group of wells in the SE part of the field, however, is distinguished by higher values of a very sensitive geochemical migration parameter, i.e., the ratio of C16 n-alkane and aromatic 2-methylphenanthrene. The comparison with the oils produced after the water flooding indicates smoothing of these differences. Observed distinctions in mobility parameter of the oils are related to higher recovery factor for the NW part compared to the SE part of the field, demonstrated by volumetric calculations. Further, significant changes in the ratio of hydrocarbon (saturate and aromatic) to non-hydrocarbon (resins and asphaltenes) fractions are found in oils produced from the SE part of the field before and after water flooding, mainly due to prominent variations in asphaltene content of the oils. These changes in oil composition are discussed in relation to production as causing short distance migration of the oil within the reservoir and the heterogeneities in reservoir permeability.

End_of_Record - Last_Page 47--------