Drawdown Test
A drawdown consists of producing a well on a constant choke after a sufficient build up (start-up) or significant increase in rate (doubling of the rate).

The reasons for doing a drawdown analysis are to determine reservoir parameters, as well as to diagnose completion issues. The common reservoir parameters are formation permeability, drainage area, boundary contacts, reservoir geometry, flow efficiency, and reservoir pressure. Completion evaluations from a drawdown consist of skin, additional pressure drop due to skin, and depth of invasion of the damage. There are two types of draw-downs, active and passive. Active draw-down's require attention and management from the operator, while passive draw-downs are achieved by just operating the well normally (to meet nominations) and mining the data for results. Active draw-downs are used for determining skin, permeability, flow efficiency, and reservoir pressure. Passive draw-downs are useful for determining boundary contacts, reservoir geometry, and drainage area.

There are important factors in determining the type of gauge necessary for a successful drawdown from the surface. These factors include knowing what information needs to be obtained from the test, the permeability of the reservoir, and if the well is naturally unloading. For surface testing in low-perm wells (<20 md) the DATAPORT™ is preferred, due to its low cost. It has sufficient resolution (.25 psi for 5k tree, .5 psi for 10k tree, and 1 psi for 15 k tree) and is able to sample every second if desired. For higher perm reservoirs, the DATATRAP™ or PR600™ is preferred, due to its .01 psi resolution and high sample frequency.

For downhole testing in low-perm wells, silicon-sapphire tools and electronic strain gauges are adequate. For high-perm wells, sapphire (not the same as silicon-sapphire) or quartz gauges are required. In addition, for wells with bottom-hole temperatures above 300F (150C), silicon sapphire tools are not recommended.

NEWS

Aug. 19th 2011 - Probe Holdings, Inc. has acquired the assets of AKS Technologies, Inc of Houston, USA, in an undisclosed cash and equity transaction.
Click here for the full release.





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