Putting Acoustic Telemetry to the Test: Design and Execution of a Subsea, Single Trip, Triple Independent Zone DST
Authors: Mintha Mark , Normann Clas 
Published: October 2024

Executing Drill Stem Tests (DSTs) of multiple independent zones in a well bore is relatively common in exploration and appraisal campaigns. From the perspective of cost, data quality and operational efficiency, obtaining dynamic data from multiple zones in a single well bore will often prove advantageous vs alternative approaches (i.e. additional wells, log / seismic based correlations, wireline conveyed dynamic testing, etc.).

When executing traditional multi-zone DST programs in subsea wells, a significant amount of time and risk (HSE, equipment issues) are introduced each time a test string is tripped in and out of hole. Each subsequent test typically requires:

Killing of the tested zone, and circulating the well Laying down bulky surface components (flowhead, coflex and redundant compensation systems or lift frames) Pulling / laying out the landing string, subsea test tree, tubing and BHA Zonal isolation installed, and if used, a packer installed for the next zone BHAs swapped out and RIH, correlated / spaced out with multiple pressure tests Subsea test tree, landing string, redundant compensators, flow head and coflex picked back up DST string fully pressure tested, cushions spotted and well perforated and cleaned up

Given such an extensive process, the desire to run multiple DST strings often collides with time and budget limitations. To overcome this, operators have attempted numerous variations of single trip multi-zone tests utilizing annular operated DST tools. The associated solutions often require sacrifices such as comingled production, intervention (wire for sleeves, plugs, etc.), unconventional tool arrangements or equipment modifications which introduce elevated risk to the operation and data.

Over the previous 10-15 years DST acoustic telemetry technology has expanded from its established function of downhole gauge data transmission to become integrated with electro-hydraulic or electro-mechanical DST tools enabling acoustic control of bottom hole assembly (BHA) components. The requirement for annular communication or intervention for lower zones in a multi-zone DST string has been eliminated with purpose built acoustic equipment enabling a new approach to test designs.

In addition to time savings, increased quantity and quality of data and operational flexibility associated with multi-zone acoustically operated BHAs, there is also a significant reduction in HSE risk by avoiding laying down / re-running multiple test strings or utilizing intervention equipment, particularly on subsea wells.

This paper outlines how acoustic telemetry operated DST tools were vetted and ultimately implemented in dynamic testing of a challenging subsea appraisal well located in a field of highly unconsolidated stacked sands. The DST design, an industry first, surpassed expectations across all metrics and proved the ability of acoustic BHAs to redefine what can be accomplished in a single test string trip. Whilst some challenges present in this paper may not be relevant to all DST operations, the benefits of an acoustically operated single trip multi-zone test design should be apparent to the reader for applications across a wide variety of DST scenarios.