Subsea Multilateral Oil Producer Evaluated With Acoustic and Production-Logging Tools
Authors: Carpenter Chris 
Published: October 2023

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 210299, “A Subsea Multilateral Oil Producer, Completed With AICD Sand Screens and Selective Inflow Valves, Is Evaluated by Combined Acoustic and Production-Logging Tools, Identifying the Sand-Producing Branch and a Tubing Leak in a Single Operation,” by Duncan Troup, SPE, Archer; Tim Griffin, SPE, Three60Energy; and Minh Pham, Aker BP, et al. The paper has not been peer reviewed.

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A horizontally completed subsea multilateral well exhibited unexpected sand production and a tubing leak, leading to the well being shut in. The complete paper discusses the novel tools and techniques used to localize the tubing leak, identify the bore responsible for sand production, and provide relative sand quantification at differing flow rates.

Well Background and History
The well was drilled and completed as a subsea producer to be tied back to an existing floating production, storage, and offloading (FPSO) vessel by means of a subsea flowline. After drilling of the first lateral, the decision was taken not to complete it. A second lateral was then drilled and completed. The main and secondary bores were drilled into different zones of the reservoir. Both lower completions used standalone sand screens, autonomous inflow-control-device nozzles, and swell packers set in open hole. Each of the lower completions was fitted with a hydraulically actuated inflow control valve (ICV) for managing production flow from the reservoir zones, providing the ability to produce each leg independently or commingle them. The upper completion is equipped with two gas lift valves (GLV) to provide artificial lift, a chemical injection mandrel, and a surface-controlled subsea safety valve (SCSSV).
After approximately 6 months of flowing the well, water cut was seen to increase and a series of “popping” events occurred in which productivity increased markedly for short periods. Significant quantities of sand soon began to accumulate in the FPSO topside facilities. Approximately 1.5 years after startup, well productivity decreased sharply over a few months while the water cut continued to increase.
As the productivity continued to decline, the leak rates exhibited by the SCSSV and one GLV fell outside the acceptable criteria. The pressure responses indicated a high leak rate. The well was shut in pending diagnostic logging and repair of the leak.

Sand-Source Investigation
The subsea wellhead of this well was fitted with an acoustic sand detector, but this had only indicated minor amounts of solids in the flowstream over the producing lifetime of the well. An extensive investigation concluded that the makeup of the collected sand was most likely to have originated in the case study well and that the amounts involved were likely to have been a contributing factor in the loss of well integrity. Because the well was producing from two different branches, a probability existed that only one of these was suffering from sand production. The well completion was designed to allow independent control of the branches by use of ICVs, so an intervention to assess the status of each of the branches with respect to water and sand production was planned, with the additional objective of diagnosing the well-integrity failure.