Phase 2 Development of the Slumped Crestal Area of the Brent Reservoir, Brent Field

Abstract

Abstract The Brent Field consists of a major, westerly dipping fault block, with a crestal area broken up into a series of slumped fault blocks. Development of these complex slumped blocks started in 1993 and to date a series of 9 roughly parallel horizontal east-west oil producers have been drilled, some of which have subsequently been converted into water injectors. Oil production to date, at a total rate of up to 100,000 b/d, exceeds the 1993 Development Plan forecast by 11%, despite poorer than expected east-west and north-south communication in some parts of the field. Key conclusions from the first phase of the development are:-–The Development Plan concept of multi-purpose horizontal wells (appraisal, production, injection) has been successful mainly because of the validity of the geological model. This has allowed optimal positioning of wells, with sand-sand juxtaposition initially providing sufficient pressure support via the West Flank.–Controlled reservoir depletion can be used as a method to establish fault block connectivity and to steer the flow of injection water. Uncontrolled depletion will lead to unwanted crossflow, ultimate recovery loss due to oil shrinkage and hazardous drilling due to large pressure differences.–The introduction of 7" monobore completions, combined with consecutive perforation and isolation of 150–250m reservoir sections, has increased ultimate recovery and reduced cost. Multi-straddle assemblies have proved to be ineffective, because communication patterns cannot be predicted accurately enough. An extensive data gathering programme has now been largely completed, consisting of new 3D seismic, borehole imaging logs, radioactive tracer injection, interference testing, advanced PLT logging and permanent downhole gauge output. This has so far resulted in an adjustment to the Development Plan in the compartmentalised Brent Horst and Graben areas, successfully targeting one water injector to support two producers 1500m apart, and in one infill well to appraise the quantity and quality of reservoir rock between the top Etive and the X-unconformity erosional surface. In combination with advanced drilling techniques a recovery factor of 50% is now considered achievable. Introduction The Brent Field consists of a major, westerly dipping fault block, with a crestal area broken up into a series of slumped fault blocks. Development of the Brent slumps started in 1993 and to date a series of 9 roughly parallel, horizontal east-west oil producers have been drilled, two of which have subsequently been converted into water injectors (see Figure 1). The wells in question are listed (in chronological order) in Table 1. They are all part of the first stage of the 1993 Development Plan (ref. 1), eventually comprising of 6 horizontal producers, interspersed with 6 horizontal water injectors. P. 135^