Build Up Test
A build up consists of shutting in a well and monitoring the pressure responses at the wellhead or downhole.

Buildup tests are used to analyze completion as well as reservoir properties / parameters. After a well has been flowing long enough to reach radial flow, the well is shut in and the pressure response is measured either from the surface or downhole or both. When the well is shut in it stops producing any hydrocarbons at the surface but still produces hydrocarbons from the reservoir through the perforations which cause the pressure in the wellbore to increase during the test. So even though the flow rate is zero at the surface there is still flow into the wellbore. For short-term tests, these pressure responses can be used to determine properties such as skin, perm, and flow efficiency. Longer-term build-ups can be used to determine boundaries and dispositions.

When measuring the pressure from surface there are some problems associated with buildup tests if the fluid is not single phase in the wellbore, like gas condensate or oil. With a gas condensate well if the gas drops below the dew point or produces significant water (more than water of condensation), liquid drop-out and re-injection are possible. If the liquid does not re-vaporize and falls to the bottom of the well, a liquid column will form. When this occurs then an accurate conversion to BHP is very difficult until the liquid re-injects below the perforations and re-establishes hydraulic communication from the gauge to the reservoir. Note: This effect is also observed in wells with downhole gauges where the gauge is positioned above the perforations.

For oil wells, re-injection is not as likely, but the formation of a liquid column during the build-up can prove challenging if testing from the surface. If the surface pressure is below the bubble point, the PR600™ gauges are recommended for a PBU. If skin, perm and Pres are the objectives, a two-rate test may be performed from the surface using the DATATRAP™, as long as both rates are above the unloading rate (see 2-rate Test section).

Wellbore cooling effects can also play a major role in measuring buildups from the surface (or in wells where the downhole gauge is set 500+ feet above the completion). Wellbore cooling causes the temperature of the gas to decrease which increases its density (increases the head). If the rate of increase in the head is larger than the reservoir signal, the observed pressure can decrease during the buildup when the bottom hole pressure is actually building (hence the test name: build-up).

Testing for reservoir limits with a build-up test is all fun and good, until you look at your cash flow. For high-perm reservoirs, these tests can usually be performed in a day or two. For low-perm reservoirs, they can take months. So, an operator has to look at the value of the data vs the cost (including delayed production) of gathering the data. If performing a build-up to determine reservoir limits, we recommend leaving the gauge in/on the well to record the drawdown when the well is returned to production. This way, you get two tests for the price of one...

Same gauge benefits as drawdown test but need to know if SITP is below Saturation Pressure or if there is high water production.


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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