Permanent Fiber-Optic DTS Evaluates Production Enhancement
Authors: Carpenter Chris 
Published: April 2023

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 31654, “Production Enhancement Evaluation Through Permanent Fiber-Optic Distributed-Temperature-Sensing Interpretation for a Gas-Lifted Producer in Field B, Offshore Malaysia,” by Chang Siong Ting, Nur’ain Minggu, and Dahlila Kamat, Petronas, et al. The paper has not been peer reviewed. Copyright 2022 Offshore Technology Conference. Reproduced by permission.

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In the complete paper, the authors evaluate the effectiveness of production-enhancement activities for Well B Long-String (i.e., Well BL) using distributed-temperature-sensing (DTS) technology. Installation of permanent fiber-optic cable across the reservoir sections has enabled gas-lift monitoring, identification of well-integrity issues, and zonal inflow profiling from perforation contribution. The effectiveness of executed remedial jobs is described along with findings and interpretations of DTS results.

Field and Well BL Background
Field B is a mature brownfield 45 km offshore east Malaysia in a water depth of approximately 230 ft. The field’s structure has a gentle rollover anticline with a collapsed crest caused by growth faulting. The reservoirs were deposited in a coastal shallow marine environment with channels. The production wells completed in these reservoirs were completed with internal gravel packs. The typical completion types for wells in Field B are dual strings with sliding sleeve doors (SSD), intended for commingled production from the multilayered reservoirs. Most of the wells in Field B were installed with permanent downhole gauges (PDGs), and five wells were equipped with permanent DTS across the reservoir section.
The well was completed in 2015 as a gas-lifted dual-string producer with a 3½-in. completion string for short string (BS) and 3½×2⅞-in. tubing crossover for long string (BL). The long string of Well B also produces from two zones, Zones 2 and 3, while the short string of Well B produces from only one zone, Zone 1. Each zone consists of sublayers. In addition, DTS fiber-optic cable was installed along the long string across the reservoir sections in Well BL, and the system enabled the operator to monitor continuously the wellbore temperature across all producing intervals. Each zone also was equipped with a zonal PDG (temperature and pressure) and SSDs.

DTS System
The double-ended DTS system was installed permanently across the multilayered reservoir in Well BL to measure the dynamic change of temperature in the near-wellbore region over time. Double-ended temperature measurement was used to correct for differential light losses (light-loss correction) that appear gradually over the lifetime of the fiber as its quality is degraded because of hydrogen darkening or exposure to high temperatures. This measure improves the quality and accuracy of the measurement signal backscattered to the surface receiver for processing. With double-ended DTS, small thermal changes over time in the well can be tracked. Temperature measurements are detected in 1.6-ft intervals along the length of the cable. This generates a profile of temperature effects along the production string by analyzing backscattered Raman wavelength light from a pulsed laser source. This DTS measurement allows continuous monitoring of production events as they happen.