This article gives a preliminary analysis of the impact of application of horizontal drilling and production techniques on the economy of offshore reservoir developments.

If we consider wells with a medium and long radius of curvature ensuring horizontal drilling in reservoirs with horizontal sections of greater than 300 m (1000 ft), theoretical research shows that flow ratios of four or more can be obtained in practice in practically all reservoirs, provided they are vertically permeable and no more than 60 m (200 ft) thick. These theoretical results agree well with what is observed in the field.

Analysis of the data available on horizontal drillings performed so far shows that offshore, the cost per metre drilled in a horizontal well tends with experience towards the cost per metre drilled in a conventional well. The excess cost of a horizontal well is essentially due to the greater length drilled.

Offshore, the capital and operating costs bear an increasing relationship to the number of wells and production level. From a model of these costs based on 28 projects in the North Sea, the impact of replacing conventional wells with horizontal wells was studied. In the case of complete development, the reduction in the number of wells for the same production flow enables the technical cost of the oil to be decreased by 2 to 8 dollars per barrel, depending on the case. The parameters of importance are firstly, the ratio of the flowrate of the horizontal well to the flowrate of the conventional well, secondly the ratio of the cost of drilling to the total cost and thirdly the flowrate of the conventional reference well.

Cases of application yielding the greatest savings are those where the share of drilling costs out of the total cost is high, over 25 % and cases where the flowrate of conventional wells is low, below 2000 Bopd.

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