Shell U.K. Exploration and Production, operator in the U.K. sector of the North Sea for Shell and Esso, is developing the tight gas reservoirs of the Barque and Clipper fields, located in the Sole Pit Basin of the U.K. Southern North Sea. Well productivity is fundamentally dependent on the intersection of dune slipface sands and/or sparsely distributed open natural fracture systems. The initial development plans were based on the use of conventionally deviated wells with cemented liners across the pay section, relying on massive hydraulic fracture stimulation, if required, to achieve economic production rates. This concept has progressively evolved towards the use of horizontal wells which increase the probability of intersecting the productive features in the reservoir. Twelve horizontal wells were drilled up to mid 1992, out of a total of twenty six development wells. The main findings are:

  • average initial deliverability of horizontal wells is significantly higher than that of conventionally deviated wells; Productivity Improvement Factors of between 2 and 7 have been realised;

  • horizontal wells decline more slowly than fracture stimulated wells;

  • Ultimate Recovery has increased by 20% relative, which is to a large extent due to horizontal wells;

  • the well count can be reduced by some 25%; this has, in combination with well cost savings through the use of slim casing schemes and the increase in UR, significantly improved the project economics;

  • additional reserves from low relief flank areas can be accessed.

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