Case History: HP/HT Underbalance Drill Stem Testing, Deepwater KG Offshore

Abstract

A leading exploration and production company in India needed to conduct high-pressure/high-temperature (HP/HT) testing on a deepwater well. Deployment of the drillstem test (DST) tools in a kill-weight mud system as a testing fluid could have resulted in challenges with tool operation and retrieval of the DST string at the end of the test. Appropriate kill-weight clear fluid was not available at the time of the project execution. This paper describes the method developed to achieve underbalance Drill Stem Testing in Deepwater KG offshore India. The data also describes careful preparation of the tool string for HP/HT environment and operation of DST tools in underbalance annulus brine. The well test was planned with the available low-density clear fluid system (brine). During pre-job planning, multiple DST tool combinations were considered before finally deploying a full-suite, multicycle DST tool string. The operation was designed to perform the DST with the underbalance testing fluid to test the reservoir potential and later to displace the kill-weight fluid into the well during well kill operations. Multicycle DST tools were deployed with a 7-in. retrievable packer, 3-in. subsea safety system, and 15K surface well testing equipment. The test string, featuring the multicycle DST tools, performed successfully with the available underbalance fluid (brine). The tools also operated as designed in the kill-weight mud, thereby meeting the defined test objectives. The testing operation was performed in a single run, reducing rig time and associated expenses to provide overall cost savings to the customer. Maximum bottomhole pressure and bottomhole temperature recorded was 11,000 psi and 365°F during this job. This was the first HP/HT underbalance well testing job carried out in a deepwater environment in India. This job provided the platform to perform similar underbalance well testing operations in a subsequent job on another deepwater well. Using the multicycle DST tool string, the customer was able to safely and effectively test the reservoir potential with an underbalanced test fluid in two deepwater wells, achieving the desired test objectives.