Gravel Pack Production History in the Balmoral Field
Authors: Wilson D.C. , Green A.A. , Thorpe D. , Shepherd C.E. 
Published: October 2008

The Balmoral Field was the first in the North Sea requiring all the development wells to be gravel packed. The wells were pre-drilled and completed prior to the hook up to the floating production vessel. Oil production started in November 1986 and there are now some 4 years of production history. This paper reviews the performance of the gravel packed wells based upon the annual production logging programmes. Explanations of the observed changes in well productivity are provided. Experience gained during this period may be of benefit to operators who are considering gravel packing producing wells and who are evaluating methods for monitoring well performance.

INTRODUCTION

The Balmoral Field is situated in Block 16/21 in the UK sector of the North Sea, some 140 miles northeast of Aberdeen. The field was discovered in 1975 and had been extensively appraised before Annex B approval was obtained in 1984. It has been developed with 13 producing and 6 water injection wells tied back to facilities on board the Balmoral Floating Production Vessel (FPV). Three of the producers and all the water injectors are satellite wells tied back to the subsea manifold with individual flowlines. The remaining 10 wells were pre-drilled through a template which is located directly below the vessel. First oil production was in November 1986, three months ahead of schedule and the plateau production rate of 35,000 bopd was achieved in March 1987.

Figures 1 and 2 detail the field's position in relation to other Central North Sea reservoirs and show the approximate field dimensions and the development well configuration.

The Balmoral reservoir is a poorly consolidated Palaeocene sandstone (Andrew Formation) at approximately 7000 feet TVD 55. It is a low relief structure formed by sediments draping over a prominent Devonian high. The oil column which reaches a maximum height of 140 feet overlies a substantial aquifer. Reservoir quality is good and relatively homogeneous, although a field wide 1ayering system has been identified. The uppermost three layers of the section are the main oil bearing zones and typically have the highest permeabilities. These upper layers are also the most consolidated.

Testing of appraisal wells indicated that sand production was a potential problem and that sand control would have to be considered during completion design. Internal gravel packs were selected for this purpose. After trials to evaluate the various gravel packing options and to assess the impact of packs on well productivity, all wells (producers and injectors) were gravel packed.

This paper reviews the production logging undertaken during the first 4 years of field life and considers the effects of the gravel pack completions on the productivity of Balmoral wells. It also provides explanations for the observed changes in productivity over this period. The paper should be considered as a continuation of SPE Paper 18382 which detailed Sun Oil's early evaluation of gravel packing, the design criteria used for the Balmoral wells and the initial effects on well PI/II of gravel packing.