Drillstem tests provide crucial information about well deliverability and reservoir characteristics, but gathering such critical data may require many days of rig time, which can be prohibitively expensive in deepwater environments. As the information gathered during the test is generally available only when the string is pulled out of hole, well test engineers are usually conservative when designing the duration of the flow and shut-in periods to ensure sufficient data is acquired to meet test objectives. However, in some cases, the planned test durations were not sufficiently long to capture the necessary reservoir data for interpretation.
A relatively common practice of obtaining bottomhole data before the end of the test is running a conventional surface readout (SRO) system on electrical cable to establish communication with the bottomhole gauges, but this technique may pose a major risk to the operations. Recently developed wireless downhole reservoir testing systems can be the solution to this challenge. The system transmits information to and from the bottomhole tools in real time with no risk to the drilling operations.
This paper describes a field case where such a system was used on a deepwater well offshore Brazil. The wireless telemetry system took less time to rig up than wireline equipment and allowed the test sequence to be adjusted during the test. The data was available during flow and shut-in periods. It was used to monitor cleanup efficiency in real time as well as to obtain key reservoir information before ending the test. The reservoir engineers were able to
■ observe perforating guns' effect on pressure and confirm dynamic underbalance ■ compute productivity when the well was flowing ■ validate that sufficient data was acquired during the initial and main buildup periods ■ eliminate the need for a wireline run ■ establish reservoir pressure after the initial postperforating flow period.
The paper reviews the benefits and limitations of the current technology and makes recommendations on how to use the technology most effectively.
