Slickline-Deployed Fiber-Optic Cable Provides First Production Profile for High-Temperature Gas Well
Authors: Carpenter Chris 
Published: March 2024

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 215512, “Slickline-Deployed Fiber-Optic Cable Provides First-Ever Production Profile for High-Temperature Gas Well,“ by Stuart Berry, SPE, Expro, and Danu Dirya, SPE, and Graeme Cowie, SPE, TotalEnergies, et al. The paper has not been peer reviewed.

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Distributed fiber-optic sensing (DFOS) allowed the continuous gathering of flow-profile information from a high-temperature, high-rate gas well. The objective of the case study described in the complete paper is to demonstrate that thermal inversion modeling can be used to produce a production-flow profile in an environment where conventional production logging is not possible. As a result of deploying DFOS, data can be acquired at more-realistic rates. Through performing of thermal inversion of distributed temperature sensing (DTS) data and analysis of distributed acoustic sensing (DAS) data, a more-accurate flow profile was achieved.

Introduction
Culzean is a high-pressure/high-temperature gas condensate field in the central North Sea. The main productive interval for the field is the Triassic Joanne sandstone deposited in a semiarid continental fluvial environment. The Jurassic Pentland sandstone deposited by meandering fluvial systems also contains significant resources.
Initial reservoir pressure was 936 bar; the temperature was 170°C. The development consists of six production wells, five from the Joanne and one from the Pentland. While the reservoir interval is relatively thick, the depositional environment created a very layered reservoir with significant variability in reservoir quality.
Flow-profile data over the reservoir has traditionally been acquired using production-logging tools with spinner velocity and pressure and temperature measurements. Production-log deployment can be problematic in high-rate wells, particularly when tubing is restricted because of pipe deformation or deposits in the tubing.
In the Culzean field, several wells were selected for flow-profile monitoring. Previous slickline operations indicated that conventional production logging would be ineffective. Modeling showed significant tool-lift risk, meaning that the well could only be flowed at approximately 25% of its normal operating rate. A previous attempted production-logging campaign in the well resulted in no valid data acquisition but incurred a direct cost of $700,000 and a deferral of 10 days production estimated at a cost of $10.8 million.
An alternative acquisition method was investigated to obtain production-profile data while minimizing risks associated with conventional production-log deployment. DFOS provides a continuous measurement over the entire length of the well for temperature and acoustic noise. A high-temperature slickline DFOS wire could allow Culzean well data acquisition under flowing conditions.

Technology Selection
Data acquisition was divided into a shut-in phase and a flowing phase. For the shut-in phase, a simplified production-logging toolstring was used to measure any crossflow over the reservoir section. The flowing phase would consist only of DAS data over the reservoir section, with a simple pressure/temperature memory tool in the sump of the well. The DFOS data would gather shut-in data before opening the well up to flow. For the conventional tool shut-in string, an inline caged spinner was selected.