Using 3D Geological Modelling and Connectivity Analysis to Locate Remaining Oil Targets in the Brent Reservoir of the Mature Brent Field

Abstract

Abstract As part of the drive to locate remaining oil targets in the Brent Field prior to depressurisation, full-field 3D static reservoir models for the main Brent Field (excluding the faultscarp degradation area called the 'slumps') were constructed last year. Both the Brent Group and the Statfjord Formation reservoirs were modelled using the Shell proprietry 3D geological reservoir and property modelling program known as GEOCAP. This paper briefly outlines the approach taken in the GEOCAP modelling of the Jurassic Brent Group Ness reservoir, which formed the basis for the first test-case application of a new well-clustering technique, CRF (Cumulative Resistance to Flow) which is the focus of this paper. The CRF module is one of the latest technological enhancements of GEOCAP, developed by RTS (Shell International Research and Technical Services, Netherlands). It is a permeability-distance based well-clustering module, that calculates connected reservoir volume to perforations, using the GEOCAP 3D permeability models. Subsequent removal of these connected rock-volume clusters from the model, results in a 3D model of unconnected reservoir volume. The model can then be used to identify unconnected areas that are large enough to be considered as potential remaining oil targets. These areas then warrant further investigation as potential target locations, most importantly in terms of dynamic reservoir modelling aspects, and calibration with latest surveillance data. The results indicate that there are still several sizeable 'targets' (in excess of 1 MMbbls STOIP) left in the Ness reservoir after the currently planned wells have been drilled and these are currently undergoing independent review. Introduction The Brent Field is currently penetrated by over 200 wells, has been in production for 20 years and has produced more than 1750MMbbls of oil. As a result of the 1995–96 LTRO (Locate The Remaining Oil) campaign, 20 wells were planned to access an estimated 50MMbbls+ recoverable oil. At the time of writing most of these wells have now been drilled. Studies covering all petroleum engineering aspects continue to try to locate and develop further remaining undrained oil prior to the year 2004, when declining pressures will cause wells to lose lift, limiting oil production. The objective of the GEOCAP modelling project for the Brent Field reservoirs was to use the powerful functionality available within the system (particularly the detailed facies modelling capabilities) to try to locate remaining unswept sands in the field. GEOCAP functionality enables the integration, synthesis and use of vast amounts of data in the geological and property modelling process: well data, petrophysical logs, core facies descriptions, core-plug data, perforations, seismic surfaces, faults (sealing/non-sealing), fluid contacts, rock property data etc. This data is then used to perform reservoir unit correlations, facies identification from logs, intra-reservoir unit detailed facies correlations and the subsequent 3D modelling of genetic facies bodies. The 3D geological model is constrained by seismic surfaces. The fundamental principle of the 3D property modelling (porosity, permeability and saturation) is that it is controlled by the 3D detailed facies model. GEOCAP also contains functionality for well-planning and well evaluation. Outline of the GEOCAP modelling process Over 130 wells that penetrate the main Brent reservoir were used to construct the 3D geological model (Fig. 1). P. 107^