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Monitoring of oil well water pressure using distributed fiber optic temperature measurement (DTS) and distributed fiber optic acoustic vibration sensing (DAS) technologies

The principle and advantages of DTS

The distributed fiber optic temperature measurement system is sensitive to temperature based on the principle of optical time-domain reflection and Raman scattering effect to achieve temperature monitoring. The entire system uses fiber optic as the carrier for sensitive information sensing and signal transmission, which has the characteristics of continuous temperature measurement, distributed temperature measurement, real-time temperature measurement, electromagnetic interference resistance, intrinsic safety, remote monitoring, high sensitivity, easy installation, and long service life. It is widely used in industries such as municipal comprehensive pipe galleries, pipelines, tunnels, cables, petroleum and petrochemical, and coal mines.

How to monitor oil well pressure

Hydraulic fracturing is a key technology for efficient development of unconventional oil and gas reservoirs and hot dry rocks. By using hydraulic fracturing to transform the reservoir and forming a fracture network structure in the reservoir, the oil and gas production of oil and gas wells can be effectively increased and the heat production of the geothermal system (EGS) can be strengthened. Therefore, the artificial fractures formed by hydraulic fracturing are a direct reflection of the effectiveness of reservoir fracturing transformation and an important basis for evaluating the production capacity of hydraulic fracturing wells. At present, methods such as microseismic monitoring and production logging are commonly used to monitor the hydraulic fracturing process and post fracturing production process. These methods have high implementation costs and complex operations, making it difficult to accurately monitor the fracturing process and production process of multi-stage fracturing artificial fractures. Moreover, microseismic monitoring belongs to far-field monitoring, which is subject to many external interference factors and has poor accuracy. Therefore, it is particularly important to seek a near-field monitoring method that can simultaneously monitor the hydraulic fracturing process and post fracturing production process.

With the development of distributed fiber optic temperature monitoring (DTS) and distributed fiber optic sound monitoring (DAS) technologies, it provides an important means for real-time monitoring of hydraulic fracturing processes and post fracturing production monitoring. The main principle of DTS technology is to use the reflection principle of optical fibers and the temperature sensitivity of reverse Roman scattering of optical fibers, relying on the quantitative relationship between the propagation of light in the optical fiber and the temperature changes around the optical fiber medium to determine the temperature at the location of the optical fiber medium. The main principle of DAS technology is to use the principle of coherent optical time-domain reflection measurement to inject coherent short pulse laser into the optical fiber. When external vibration acts on the optical fiber, the internal structure of the fiber core will be slightly changed due to the elastic optical effect, resulting in changes in the back Rayleigh scattering signal and changes in the received reflected light intensity. By detecting the intensity changes of the Rayleigh scattering light signal before and after the downhole event, the current downhole fluid flow event can be detected and accurately located, thus achieving real-time monitoring of downhole production dynamics. Due to its characteristics of anti electromagnetic interference, corrosion resistance, and good real-time performance, optical fibers have greater advantages in dynamic real-time monitoring of underground production.

During hydraulic fracturing, a large amount of low-temperature fracturing fluid enters the high-temperature formation, resulting in a decrease in temperature around the fracturing interval; At the same time, when fracturing fluid enters the fracturing layer to create fractures, extend fractures, and flow in fractures, a large amount of noise is generated. The larger the cracks formed by the fracturing layer, the higher the temperature drop and the greater the noise amplitude. The use of highly sensitive and high-precision distributed fiber optic temperature and sound sensing technology can monitor in real time the position and quantity of ground layer fracturing, as well as the volume of fracturing fluid entering the fracturing formation, and thus infer the approximate geometric parameters of the cracks.
During the post production process, a large amount of fluid in the reservoir flows into the wellbore through cracks instead of reservoir matrix. When the fluid flows through the dense reservoir matrix and through cracks filled with proppants, different frequencies of noise are generated due to the physical differences in the medium, and the intensity of the noise is related to the flow rate; In addition, due to differences in reservoir temperature, thermal characteristics of oil and water, and density of oil and water, fluids with different flow rates and compositions will exhibit different temperature and sound velocity differences when flowing into and in the wellbore from cracks at different positions. By using high sensitivity and precision distributed fiber optic temperature and sound sensing technology, this temperature and sound velocity difference can be perceived, and then combined with corresponding mathematical models for interpretation, the production profile of the fractured well can be obtained, and effective fractured intervals can be determined and the fracturing effect evaluated.

Characteristics of DAS distributed fiber optic acoustic vibration sensing host system

The DAS distributed fiber optic acoustic vibration security sensing detection system can accurately locate the location of the incident, with high accuracy, fast response time, immunity to electromagnetic interference, electrical insulation, fiber optic nature, and explosion-proof characteristics. Therefore, it can be directly used in environments with different levels of perimeter security needs.

The DAS fiber optic perimeter security sensing system consists of distributed fiber optic hosts, detection optical cables, etc. The distributed sensing system is widely used and reasonably priced.

DAS distributed fiber optic acoustic vibration sensing host system product functions

1. It can monitor vibration over long distances, with high positioning accuracy and stable system operation;

2. 24-hour real-time online monitoring without the need for manual duty, automatic alarm or device activation when exceeding the upper and lower limits of the warning, achieving high efficiency;

3. Short training time and convenient software operation;

Characteristics of DAS distributed fiber optic acoustic vibration sensing host products

1. FJINNO DAS fiber optic demodulator adopts independently developed advanced chips, which have fast processing speed, high reliability, and low power consumption;

2. Fiber optic sensors themselves have characteristics such as electrical insulation and immunity to electromagnetic interference, and can be directly used in hazardous materials such as petrochemicals;

3. Not easily affected by external environment.

Traditional temperature sensors are easily affected by lightning, especially for electrical temperature sensors. Distributed fiber optic sensors are completely electrically insulated and can resist the effects of high voltage and high current;

4. The laying density of fiber optic sensors can be set independently to meet the actual needs of various temperature measurement hotspots;

Application field of DAS distributed fiber optic acoustic vibration products

Online monitoring of natural gas pipeline leaks

Online monitoring of oil pipeline leaks, etc.



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