Advanced wireless telemetry system for real-time surface readout during drill stem testing

Abstract

Drill stem testing (DST) provides reservoir information that helps evaluate the potential of a new field. The data includes permeability, total skin (damage) and formation pressure, but these calculations are possible only if the build-up period is sufficiently long to attain middle time regime. The best technique for determining the length of flowing and build-up periods required is to monitor real-time bottomhole pressure (BHP) at surface. Traditionally, BHP and temperature data have been recorded using downhole memory gauges, but the data could only be retrieved after the test had concluded and the DST bottomhole assembly (BHA) was pulled out of hole. Wireline surface read-out (SRO) was used in the next evolution of the applicable technology. This method lowered a wireline retrieval tool into the BHA during the build-up periods to retrieve real-time data from downhole gauges. This technique worked satisfactorily during build-up periods but was difficult to achieve during flowing periods, especially at high rates and with sand or solid production. Now, a real-time downhole data acquisition solution that uses the newest generation of an acoustic wireless telemetry system has been developed. This system allows data transmission by the tubular wall using acoustic energy during flowing and build-up periods, thus providing real-time SRO throughout the test to facilitate quick decisions and troubleshooting solutions. With the acoustic wireless telemetry system, wireline intervention during DST is not required, thus eliminating inherent risks and costs of such operations. A project undertaken by PETRONAS and a major service company using this system was successfully implemented on jack-up rigs in Malaysia. This paper discusses the challenges and step-by-step improvements made to enable these jobs to successfully meet the sought-after goals.