Vertical permeability is an important input to coning and water influx studies and also choice of perforation policy. For British Gas Exploration and Production knowledge of this parameter is important for a number of small gas fields underlain by very large aquifers where water influx could significantly reduce reserves.

Conventional ways of measuring Kh/Kv (anisotropy) at reservoir scales have either proved unsuccessful or can only be undertaken once differential depletion effects become apparent.

A new openhole testing technique is described. It uses a dual inflatable packer run with a wireline formation tester as part of the logging program. The measurement scale is greater than that for core measurements and offers both versatility and precision to measure anisotropy within and between selected reservoir units at in-situ conditions.

The technique and analysis are briefly described, and results compared with other sources of permeability data. The paper concludes that this type of interference test can provide valuable and timely data that reduces the risk involved in a development decision and the cost of using conventional testing equipment.

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