Survivability of Optical Fiber for Harsh Environments

Abstract

Today, optical-fiber systems are used in the oilfield for sensing and telemetry applications. The most commonly used downhole is the distributed temperature sensing (DTS) system which collects permanent real-time temperature well logs. These logs are extremely useful for real-time production allocation, heavy oil thermal recovery (e.g., steam-assisted gravity drainage, SAGD), steam-well management, and well-integrity monitoring.Unfortunately, optical fibers are not immune to degradation under downhole conditions. Hydrogen, present in the wells because of corrosion or other factors, can attack the optical-fiber components causing attenuation increase. This attenuation can have a negative effect on the performance of the system, such as decreasing accuracy or resolution. Understanding the process and the impact of this degradation is of great importance to the reliable operation of these optical-fiber systems.This article shows how a combination of controlled testing and modeling calculations can be used to provide an estimation of the attenuation increase expected from the fiber with time and downhole conditions.Test results for attenuation of optical fiber in hydrogen atmospheres and under downhole temperatures will be shown. The article also provides results from the testing of a new optical fiber that was designed to give a considerable improvement in resistance to hydrogen attack. These results give an order of magnitude improvement in comparison with commercially available optical fibers. Early field tests are consistent with the results of the study.

A Review of Distributed Fiber–Optic Sensing in the Oil and Gas Industry

“…Other technical challenges include the fiber darkening downhole [76], where hydrogen penetrates the metal tube around the fiber and fiber jackets to enter the fiber material causing a significant optical attenuation. However, many efforts have been reported to tackle the hydrogen darkening by using hermetic coating, tailoring the glass properties, and selecting proper operation wavelengths [122]. Such optical fiber cables with special coating and properties are now readily available for long-term downhole monitoring.…”

Gamma Sensing Characterization of Cerium-Doped Silica Scintillating Fiber

“…随着伽马辐射探测技术在医学放疗、 石油测井、 工业探伤及核能设施安全监控等领域的广泛应用 [1][2][3] ， 人 们 对 伽 马 辐 射 传 感 器 件 的 功 能 提 出 了 越 来 越 高 的 要 求 ， 如 在 核 能 设 施 伽 马 辐 射 监 控 应 用 中 ， 需 要 将 辐 射 传 感 头 与 光 电 转 换 器 件 分 离 从 而 实 现 远 程 实 时 监 控 ； 在 石 油 测 井 应 用 中 ， 需 要 辐 射 传 感 头 可 工 作 于 高 温 高 压 环境 [4] ； 在医学放疗应用中， 需要微小尺寸传感头进行在体检测辐射剂量等。 基 于 闪 烁 光 纤 的 光 纤 传 感 器 利 用 了 闪 烁 体 对 伽 马 辐 射 敏 感 、 体 积 小 和 与 导 光 光 纤 易 于 耦 合 等 特 点 ， 为 实现远程、 恶劣环境的辐射监测提供了可能 [5][6] 。然而， 目前的闪烁光纤受材料和制备工艺等因素的制约， 只 在放射性诊疗和高能物理实验等环境稳定安全的有限领域实现了应用 [7] ， 而在其他诸如工业安全、 石油开采 和核工业等特殊环境中的应用还有局限性。 中 国 激 光…”

Comparative Experimental Study of a High-Temperature Raman-Based Distributed Optical Fiber Sensor with Different Special Fibers

“…Polyimide coating is very common, but it is limited to applications where temperature does not exceed 300 °C, according to the technical specifications of the manufacturers of these fibers. Additionally, polyimide-coated fibers are not impermeable and can undergo core hydrogen penetration, which increases attenuation in certain wavelengths of the infrared spectrum and reduces fatigue stress resistance [19]. To prevent the problems associated with hydrogen penetration a coating of carbon is applied to the fiber during manufacturing to block the entry of water and slow down the diffusion of hydrogen.…”