Case History: First Isochronal Reservoir Test Successfully Performed Worldwide at a Bottomhole Temperature Greater Than 430° F

Abstract

Abstract Gujarat State Petroleum Corporation, Ltd (GSPC) wished to evaluate a reservoir in an offshore well on the Indian East Coast where bottomhole temperature was more than 433°F. The Initial DST had shown significant potential for the zone of interest; and therefore, GSPC decided to perform isochronal testing to obtain more detailed reservoir pressure information. In this environment, the DST tools would be required to function continuously in the high-temperature conditions for more than 16 days in order to retrieve the required data without interruption. These conditions would definitely challenge the capabilities of the currently available drill-stem testing (DST) equipment. This paper describes how DST tools rated to 450°F-bottomhole temperature and 15,000-psi differential-pressure were configured to maintain integrity and successfully evaluate the well. The tools were annulus pressure responsive (APR) that would be operated with pressure applied to the annulus from the surface. The string included a multi-cycle downhole tester valve, a multi-cycle circulating valve, a blowout preventer (BOP) safety valve, a tubing tester valve, a secondary circulating valve, and safety circulating valves. The multi-cycle circulating valve added the flexibility to displace the string with nitrogen for well stimulation, if the well did not flow. The data describes the careful preparation of the toolstring, the extreme conditions in which the DST tools had to operate to evaluate the well successfully, and how the meticulously prepared toolstring was capable of meeting GSPC’s requirements. The DST tools performed satisfactorily for more than 16 days during the test. This job set a world record for the service company for a reservoir test performed in these high-temperature conditions and may have set a world record for all testing operations performed by other service companies as well. Advantages included elimination of coiled tubing, increased safety for this type of operation, and a reduction of rig time compared to other testing jobs.