Simultaneous measurement of down-hole pressure and distributed temperature with a single fiber

Abstract

A cost-effective sensing system combining the fiber Fabry–Perot interferometer-based pressure sensor with the distributed temperature sensor is presented. This sensing system can realize accurate pressure measurement of the oil reservoir and temperature profile measurement of the wellbore simultaneously. For the sensing wave bands of the pressure and temperature sensor are different, the wavelength-division multiplexing (WDM) technology was used to couple the two sensing signals into one single fiber. As the wavelength difference between Stokes peak and anti-Stokes peak is larger than the bandwidth of commercial WDM, a wide bandwidth WDM with gain flattening range up to 80 nm was custom-made. Experimental results showed that this sensing system can reach 0.1% accuracy for the pressure measurement with a 0–30 MPa working range and 1 °C accuracy for the temperature measurement in a working range from room temperature to 300 °C. Additionally, a resolution of below 1.4 kPa for the pressure measurement and 0.5 °C for the temperature measurement had been realized. Field test results showed that this sensing system also has good long-term stability in high-temperature environment down hole.

A Survey on Subsurface Signal Propagation

“…This is a cost effective solution as it senses both temperature and pressure simultaneously. The results in [271] proves that the techniques is stable and accurate. An down-hole monitoring system was deployed in shoreline of Marmara sea, Turkey, using optical fiber.…”

“…where p denotes the pressure. In [271], information from two fibers is combined onto one by using wavelength division multiplexing. They uses it for the temperate and pressure sensing in well-bore.…”

Fiber optic sensing technologies potentially applicable for hypersonic wind tunnel harsh environments

“…Since the beginning of the 1990s, universities and research institutes in China have started the study on FPI fiber optic sensors, and many of them have been applied to the fields of bridges and oil wells for strain/pressure measurements [18,19]. Dalian University of Technology has developed a sensing system combining the FPI based pressure sensor [20,21] with the distributed temperature sensor, which can reach 0.1% accuracy for the pressure measurement with a 0-30 MPa working range and 1°C accuracy for the temperature measurement in a working range from room temperature to 300°C; additionally, a resolution of below 1.4 kPa for the pressure measurement and 0.5°C for the temperature measurement has been realized. And this sensing system has now been successfully applied in Liaohe and Xinjiang oil wells.…”

Monolithic Structure-Optical Fiber Sensor with Temperature Compensation for Pressure Measurement

“…For the FPI fiber sensor, the diaphragm will deflect due to the applied pressure. If the diaphragm is clamped in a rigid, round shape, the deflection of the diaphragm center, Y , under the applied pressure, P , can be expressed as [28] Y=3(1−μ2)P16Eh3(a2−r2)2, where μ , E , h , and a are the Poisson’s ratio, the Young’s modulus, the thickness, and the effective radius of diaphragm, respectively, and r is the radial distance to the diaphragm center. The L value will change with the deflection of the diaphragm when the environmental pressure is applied to the FPI sensor.…”