The paper presents two technical advances applied to downhole DST equipment:
Surface Read Out (SRO) with Wireless Transmitted Data (WTD) where pressure/temperature measurements are received in real-time, using electromagnetic transmission through the formation.
High temperature DST string and memory gauges.
A test program was carried out with WTD in the Middle-East, where it was important to get pressure data in real-time during the test. Due to the presence of an ESP to flow the well, the selected solution was a real-time pressure/temperature electromagnetic transmission tool which gave very positive results for
monitoring the complete operation.
obtaining accurate data in real-time.
optimizing the test program and the duration of the test.
The second part of the paper describes technical advances applied to components of the DST string and to the memory gauges.
There are some situations where drill stem testing can be difficult to operate. This is the case with special test operations on non flowing wells using downhole pumping, or with high temperature wells.
Newly available technical advances help in solving these problems, as well as improving the quality of pressure measurements and optimizing the cost of the test by reducing its overall duration.
While running the DST, the operator assumes that various actions initiated from surface with pressure surges or mechanical actions on the drill string, have been properly implemented downhole. He has very limited control of the downhole situation, most of the time unable to detect malfunctioning of packer setting and sealing, valve operation, etc…. These problems, when they occur, are sometimes identified only after retrieving the memory gauge, downloading the measurements and analyzing the data. All this process may take several days and, in the worst case, could result in having to repeat the test.
Besides, when using memory gauges, the duration of build-up is pre-programmed with a large safety margin, sometimes twice as much as needed; this may represent days of precious rig time.
Surface Read Out (SRO)
The technical answer to these problems was addressed many years ago with a combination of downhole transceiver and surface read out systems, linked with an electric cable positioned inside the pipes.
The surface panel gives a real-time read-out of the down hole pressure & temperature measurements. This continuous monitoring of the testing operation brings a lot of advantages:
controlling the quality of downhole measurements
detecting malfunctioning of packers, valves, etc..
checking the build-up behavior and optimizing its duration.
This cable/SRO operation requires special equipment such as wet or inductive connectors, a special or modified test valve, and also needs additional installation time for setting up the cable.
However, such a system raises concerns about reliability and safety, with a cable located in the production flow. It might even be inadequate for use in large flows, restricting the measurements to shut down periods, or in the presence of H2S that could damage the cable.