Published: 03/20/2018
Published: 03/20/2018
An operator in the Middle East and North Africa (MENA) was typically completing multiple zones in a sandstone reservoir. In a well completed in three zones, the middle zone was determined to be oil bearing, and a reservoir test was crucial to validate its potential and measure the reservoir pressure.
Testing the target middle zone required isolating it by setting a plug below it and a packer above the top of the perforated interval. However, the open perforations of the uppermost zone would have prevented conventionally operating the downhole tools in a standard drillstem test (DST) string with annulus pressure. The open perforations above the packer posed a high risk for losing the annulus pressure pulses, typically requiring operators to isolate them by squeezing cement or performing other mechanical methods.
An additional complication for conducting the DST was that the well was not expected to flow to surface in consideration of the relatively low reservoir pressure in the zone in a neighboring well. Consequently, knowing when to end the test to prove the reservoir potential was a challenge.
Schlumberger recommended using the Symphony testing string united by Muzic telemetry to operate the downhole tools with acoustic signals controlled by the test engineer. With this wireless telemetry technology, the operator could conduct the test with open perforations above the packer instead of defaulting to the uncertainty of using annulus pressure pulses for control.
The Symphony testing Measure wireless quartz gauges were included in the test string to acquire high-precision bottomhole pressure and temperature data, which was transmitted by Muzic telemetry to surface for real-time analysis. Additionally, to follow the operator’s test program, Schlumberger incorporated the Control wireless dual valve, which provides independent command of a test valve and a circulating valve in the toolstring. Both valves were wirelessly enabled by Muzic telemetry.
Using the Symphony testing string united by Muzic telemetry, the operator individually tested and evaluated the potential of the reservoir’s middle zone. The test and circulating valves of the Control dual valve were activated multiple times per the test program. The confirmed operation of the valves avoided any waste of time in checking whether a mechanical problem was preventing the well from flowing during the test.
As expected, the well did not flow to surface. The operator avoided the lengthy traditional procedure of closing the well at surface and monitoring the wellhead pressure to ascertain whether the well is dry or has low reservoir pressure, which would be indicated by pressure buildup at the wellhead. Instead, the real-time bottomhole pressure returned by Muzic telemetry made it easy to determine the well’s potential. The operator was able to end the test with certainty after only three days when the reservoir pressure was reached.
Challenge: Employ downhole test tools to evaluate the middle zone of a reservoir without relying on annulus pressure pulses that could be lost in the overlying interval of open perforations.
Solution: Use Symphony live downhole reservoir testing string united by Muzic wireless telemetry to activate downhole tools, including the Control wireless dual valve for independent command of the test and circulating valves, and transmit data in real time.
Result: Determined the well’s potential in only three days of testing by evaluating the reservoir pressure using real-time bottomhole pressure measurements.
