Application solution of optical fiber distributed temperature measurement technology in leak point monitoring of thermal pipeline

Heat pipeline is a pipeline that transmits heat medium such as steam or superhot water. After many years of urban transformation, heat pipelines in large and medium-sized cities are mostly laid underground, including pipe trench laying and direct buried laying. In the process of use, thermal pipelines will be subjected to high temperature, wear, physical and chemical effects, coupled with the disturbance of surrounding underground engineering construction and ground traffic dynamic load, thermal pipelines will gradually produce cracks, deformation, joint damage and other defects, and then evolve into fracture, water leakage and other accidents. If a large number of pipeline leaks or even breaks during the heating period, due to the high temperature, high pressure and fast flow rate of the heating medium, it often makes the rescue difficult, and the harm of hot water to other underground public facilities is also great, and the loss is incalculable. In recent years, the leakage accident of heat pipeline shows an increasing trend:

At about 3 PM on April 22, 2012, a thrilling scene occurred in front of Huadian Qingdao Power Generation Co., LTD., Hangzhou Branch Road, Qingdao, Shandong. With a loud bang, an underground thermal pipe burst, and the hot air rolled up a large number of stones and bricks into the sky, one of them was unfortunately hit by flying stones and died after the rescue failed.

April 1, 2012: A piece of pavement on the east side of Wuhua Building, Beishi Road, Beijing suddenly collapsed. Ms. Yang Erjing, who was walking by, fell into a pit full of hot water and was severely scalded. She died at the age of 27 after all-out rescue in the hospital. After investigation, it was determined that this was a production safety responsibility accident. The reasons were the damage of the thermal pipeline, cracks and water leakage, the collapse of the soil under the sidewalk caused by hollowing out, and the daily maintenance of the thermal pipeline by the property management company was not in place, leading to the accident.

◆ On December 16, 2011, near the railway bridge on the west side of the intersection of North Second Ring Road and Xinbengbu Road, Hefei City, an excavator cut through the underground heat pipeline when breaking the road surface, and suddenly a steam above 200℃ was spewed more than 10 meters high. The accident led to the interruption of heat supply to eight social enterprises, which had a major impact on people's lives.

◆ At around 9:30 am on March 16, 2011, the heat pipeline at Sidaokou Intersection in Haidian District, Beijing burst, and a large amount of hot water gushed out.

The techniques and methods used in pipeline engineering monitoring at home and abroad are changing from the traditional point instrument

The monitoring is developing in the direction of distributed, automated, high-precision and remote monitoring. Distributed optical fiber sensing technology is a new type of real-time online monitoring technology. The detection cable is laid along the thermal pipeline in parallel, which can realize real-time monitoring of abnormal conditions such as vibration, leakage and hot spot along the pipeline. It has the advantages of long measurement distance, continuous distributed measurement, simple installation, safe and reliable, strong scalability, etc., and will not cause any damage or influence on the buried pipeline

Based on the industry's advanced distributed optical fiber sensing technology, the temperature sensing cable and vibration cable are laid along the line line of the thermal pipeline to monitor the temperature distribution and vibration around the pipeline in real time. When the temperature anomaly occurs locally in the thermal pipeline or when the damage event near the thermal pipeline that may endanger the safety of the pipeline occurs, the distributed optical fiber sensing monitoring system can timely capture these anomalies. It is displayed on the temperature curve or vibration signal, and the location information of the abnormal point is located, which is convenient for pipeline maintenance personnel to timely repair and handle, and avoid major accidents. Monitoring objectives include:

◆ Real-time online temperature distributed monitoring;

◆ Real-time online vibration monitoring near the pipeline;

◆ Clearly indicate the location of hot spots or abnormal pipes;

◆ Provide early detection of pipeline anomalies;

◆ Safety protection of heat pipeline by manual excavation;

◆ Mechanical excavation thermal pipeline safety protection;

◆ Vertical and horizontal mechanical drilling thermal pipe safety protection.

When the pipe wall thickness of the heating pipeline is thinner, the joint is broken or the insulation layer is damaged, the temperature of the local pipe section will be abnormal, and the temperature measurement optical fiber sensor will be used

The fiber-optic F-P pressure sensing system and distributed fiber-optic temperature sensing system constitute the downhole temperature and pressure measurement system

In the 1980s, researchers in the field of optical fiber developed a method for measuring temperature along optical fibers, which was combined with some oil and gas well completion techniques in the early 1990s. With no moving parts or downhole electronics required, distributed temperature sensing technology (DTS) relies on a single laser and a continuous optical fiber to collect spatial temperature distribution data. Unlike wireline logging, distributed fiber-optic temperature sensing systems measure wellbore temperatures sensitively, allowing operators to obtain temperature data for every meter (3.3 ft) in the well at regular intervals. This uniform sampling feature of the DTS system allows it to determine when and where temperature changes occur, giving the operator a better understanding of what is happening in the well.

Distributed fiber sensing technology has been used in the oil field for more than 20 years, including BP, Shell, Chevron, Schlumberger, Weatherford, Halliburton, Baker Hughes and other companies have applications.

In 1995, distributed fiber optic sensing technology was first commercially applied in a California oil well, where downhole temperatures exceeded 260 ° C.

In 1999, DTS was installed in well M-17 of the Wegifam Oil field operated by BP.

In August 2002, Noskheide ASA installed DTS in Osburg, in the Norwegian sector of the North Sea, to provide temperature data along the entire wellbore.

Since 2002, after nearly ten years of continuous improvement, DTS technology at home and abroad has developed rapidly, and has been applied to the world

In every oil well. Domestic companies such as Liaohe Oilfield and Xinjiang Oilfield began to apply DTS to downhole monitoring of heavy oil thermal production Wells.

The optical fiber F-P sensor is connected to the end of the temperature measurement cable, and the advanced distributed optical fiber temperature measurement technology and optical fiber F-P pressure measurement technology are combined to realize the same temperature and pressure measurement by using only one optical cable, which can reduce the purchase cost of optical fiber and reduce the installation operation time, especially for the monitoring of oil Wells underground

Distributed optical fiber temperature measurement system has a relatively large advantage, but because of distributed optical fiber temperature measurement system (DTS), maintenance and construction is more simple, the cost is relatively high

Low, the optical fiber itself is a sensor, set transmission and sensing together, the sensor itself is more reliable. Therefore, comprehensive advantages and disadvantages of all aspects, distributed fiber temperature measurement system

System (DTS) is more suitable for real-time temperature monitoring.

Optical fiber F-P cavity pressure sensor measurement principle: When the external pressure changes, the size of the F-P cavity changes, resulting in a change in the spectrum reflected by the fiber optic sensor. The reflection spectrum is received by the ground demodulation instrument, and the pressure at the location of the sensor is obtained through wavelength demodulation and calibration.

The optical fiber F-P pressure sensing system and the distributed optical fiber temperature sensing system constitute the downhole temperature and pressure measurement system. The topology of the system is shown in the following figure, taking the observation well as an example.

The temperature measuring cable and fiber optic F-P pressure sensor are placed in the mine at the same time, and transmitted to the central control room through fiber optic cables. The central control room is equipped with a distributed fiber optic temperature sensing system and F-P pressure demodulation instrument to jointly realize the simultaneous monitoring of underground temperature and pressure. The temperature and pressure information measured in real time by the distributed optical fiber temperature sensing system and the F-P pressure demodulation instrument is transmitted to the remote server through the wireless transmission terminal or the local area network of optical fiber communication in the oilfield, and released for the analysis and research of the data by the relevant researchers in the oilfield

Optical fiber F-P cavity pressure sensor measurement principle: When the external pressure changes, the size of the F-P cavity changes, resulting in a change in the spectrum reflected by the fiber optic sensor. The reflection spectrum is received by the ground demodulation instrument, and the pressure at the location of the sensor is obtained through wavelength demodulation and calibration.

The optical fiber F-P pressure sensing system and the distributed optical fiber temperature sensing system constitute the downhole temperature and pressure measurement system. The topology of the system is shown in the following figure, taking the observation well as an example.

The temperature measuring cable and fiber optic F-P pressure sensor are placed in the mine at the same time, and transmitted to the central control room through fiber optic cables. The central control room is equipped with a distributed fiber optic temperature sensing system and F-P pressure demodulation instrument to jointly realize the simultaneous monitoring of underground temperature and pressure. The temperature and pressure information measured in real time by the distributed optical fiber temperature sensing system and the F-P pressure demodulation instrument is transmitted to the remote server through the wireless transmission terminal or the local area network of optical fiber communication in the oilfield, and released for the analysis and research of the data by the relevant researchers in the oilfield