Formation Testers vs. DST - The Cost Effective Use of Transient Analysis to Get Reservoir Parameters

Abstract

Abstract The use of formation testers to get vertical pressure profiles, mobilities, in-situ fluid samples and vertical permeabilities is well known in the industry. Several tools are designed with multiple sample chambers and multiple probes to achieve the above objectives. In Norsk Hydro, there has been limited use of the mobility, k/, typically because this is a measurement in the "damaged zone". This measurement is also influenced by mud filtrate and is assumed normally to represent a too low value of permeability. The aim has therefore been to get a pressure transient that extends past the damaged zone and into virgin rock and fluid for a good permeability estimation. Data collected from the North Sea, using a single probe in open hole, proves radial flow after only short durations. Typically, a drawdown and buildup sequence lasts for one hour or less, and radii of investigations have been proven up to 90 meters. Permeabilities in good agreement with the average of core plugs over the same interval were obtained. Also, examples of pressure transients from several intervals in a low permeability turbidite sand will be shown to exhibit outer boundary effects at only short radii of investigations. In the examples shown, the welltests (DST) were canceled because the objectives were met using the formation tester (FT). P. 65