VARIATIONS IN THE ELECTRICAL BEHAVIOR OF THE EKOFISK FIELD IN THE NORTH SEA.

摘要

Laboratory measurements on a limited number of core plugs often present an incomplete and possibly inaccurate description of the electrical properties used for the interpretation of open- hole well logs. This paper presents the methods and results of an extensive field-wide study for the highly fractured Ekofisk field to better understand the variation in the resistivity properties throughout the chalk reservoirs. Core plug preparation and accurate determination of the resistivity and fluid saturation utilized conventional laboratory methods. The use of extracted core plugs, refined oil, and synthetic brine to simplify the testing was supported by the direct comparison of resistivities from laboratory measurements with conventional well log resistivities. The laboratory results also showed that the formation factor varied with the mineralogical content of the chalk. Non-Archie electrical behavior was observed in the chalk after imbibition. The water saturation exponent after an imbibition waterflood diverged significantly fiom that at initial water. A comparison of the histogram of after imbibition laboratory measurements with an independent well log determination of the water saturation exponent for a water flooded zone supported the laboratory measurements. This study developed a data base of measurements on 200 plus core plugs fiom which correlations and techniques can be hrther developed to improve conventional well-log interpretation for the field.