Summary

This paper describes the perforation, under drawdown, of Beatrice production wells. In view of the long completion intervals, tubing production wells. In view of the long completion intervals, tubing conveyed perforating guns are used.

A technique has been developed which enables perforation to be carried out under controlled underbalance conditions and allows well clean-up by means of a subsequent free-flow period. This, together with a pressure build-up, enables the well productivity index to be determined, and hence aids sizing of the electrical submersible pump. This is necessary to ensure that the pump operates within its recommended range.

To date, nine production wells have been perforated using tubing conveyed guns. It is shown that this technique has resulted in a significant improvement in productivity when compared to wells which have been perforated overbalanced. It is likely that this also enhances the life perforated overbalanced. It is likely that this also enhances the life of the electrical submersible pump by reducing the pump loading.

Introduction

The Beatrice oilfield is located 12 miles offshore in the Moray Firth, Scotland (Figure 1). The development comprises 3 fixed steel platforms with production being pumped to Nigg Oil Terminal via a 16" pipeline. Production from the field commenced in September 1981. Production from the field commenced in September 1981. Oil occurs in 10 vertically discontinuous, well consolidated, Jurassic sandstone accumulations (Figure 2). Large permeability contrasts exist both between and within individual units. Wells are completed in two groups of reservoir zones; viz the upper and lower zones. Thus production from up to 8 zones can be commingled.

In order to achieve satisfactory production, rates have been enhanced by installing electrical submersible pumps (ESP's) in all 23 producers. Reservoir pressure support is achieved via 12 water injectors.

Perforation technique is crucial to deliverability, especially in wells Perforation technique is crucial to deliverability, especially in wells with low to intermediate productivity. It has been demonstrated (1) that perforating under drawdown conditions is effective in reducing the skin perforating under drawdown conditions is effective in reducing the skin damage inherent in the perforation process.

This paper documents the salient factors which need to be addressed when designing perforation procedures, and details those adopted during the development of the Beatrice field. It is shown that the use of tubing conveyed perforating guns has improved the flow efficiency by reducing skin damage.

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