Controls on matrix and fracture flow from geochemical analysis of produced oil Max Coleman University of Reading The project started in January 2000, however, routine oil sampling was not established until the beginning of March. We have made chemical and isotopic analyses of trace water from four wells, spanning a range of expected contributions from matrix and fracture porosity. Initial data show that water cut varies between wells from 3% to 12%, while total salinity of these sodium chloride brines, covers a range from 58,000 to 67,000 mg/l, approximately twice that of seawater. Cl varies from 35,000 mg/l to 40,000 mg/l and has a significant correlation with water cut but, interestingly, there is no relation with sodium. Trace components also vary: alkaline earths (Mg, Ca, Sr, Ba) all show significant positive correlations with Cl; K shows a negative correlation. The relative variation of these trace components ranges from 35% to more than 250%. Chlorine stable isotope compositions also show a positive correlation with Cl concentration. These data imply that there have been at least two processes producing mixtures which involve reactive and conservative components of mixtures. However, so far there are no discernible variations of compositions with time. Consequently, we have decided to extend the range of wells to be sampled, adding five more. The experimental programme has started and both trial samples (Henley Chalk) and core samples have been delivered to Ecole Polytechnique. An experimental protocol has been established for varying axial and confining pressures to create and open fractures and to then close them. The set-up conditions are being determined currently.
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