Steam assisted gravity drainage (SAGD) is a very promising way for the development of heavy oil, extra heavy oil and tight oil reservoirs. Proper monitoring of the SAGD operations is essential to avoid operational issues and improve efficiency. Among all the monitoring techniques, micro-seismic monitoring and related interpretation method can give useful information about the steam chamber development and has been extensively studied. Distributed acoustic sensor (DAS) based on Rayleigh backscattering is a newly developed technique that can measure acoustic signal at all points along the sensing fiber. In this paper, we demonstrate a DAS system based on dual-pulse heterodyne demodulation technique and did field trial in SAGD well located in Xinjiang Oilfield, China. The field trail results validated the performance of the DAS system and indicated its applicability in steam-chamber monitoring and hydraulic monitoring.
Distributed optical fiber sensing system (DOFS) has great potential in areas of petroleum exploration and ocean defense.
By algorithm optimization in different coding environment, the multi-point and real-time heterodyne demodulation of
DOFS is achieved. In experiments, the length of the optical fiber is 500m, the spatial resolution is 5m and the system
sampling rate is 200kHz, under which condition the data rate reaches up to 160MB/s and the system can stilled be
demodulated timely. Based on this, by plotting the three-dimensional diagram (vibration intensity versus time and space),
the whole DOFS can be detected continuously and accurately.
In this paper, we propose a new type of push-pull structure fiber optic accelerometer based on 3×3 coupler for the first time and carried out measurements of its responsivity and cross-axis sensitivity. With specific algorithm, the phase signal of the sensor can be extracted without complicated modulation and demodulation. Experiments show that the responsivity of the accelerometer is larger than 40dB (0dB ref 1rad/g) within the frequency band from 10Hz to 800Hz, which agrees well with the theoretical analysis. In addition, the cross-axis sensitivity can be optimized as low as about -30dB due to the push-pull structure. The results reported here indicate that this type of fiber optic accelerometer can be applied in vibration sensing such as micro seismic monitoring.
A phase-sensitive optical time-domain reflectometry (Φ-OTDR) system using dual heterodyne pulses combined with heterodyne demodulation is proposed. The theory of this system is analyzed. The experimental results show that this system can achieve a very large dynamic range with a frequency range of 50 Hz to 25 kHz and an amplitude range of 0.9 rad to 73 rad. At the same time, multi vibrations at different locations can also be well detected.
The properties of noise induced by stimulated Brillouin scattering (SBS) in long-range interferometers and their influences on the positioning accuracy of dual Mach-Zehnder interferometric (DMZI) vibration sensing systems are studied. The SBS noise is found to be white and incoherent between the two arms of the interferometer in a 1-MHz bandwidth range. Experiments on 25-km long fibers show that the root mean square error (RMSE) of the positioning accuracy is consistent with the additive noise model for the time delay estimation theory. A low-pass filter can be properly designed to suppress the SBS noise and further achieve a maximum RMSE reduction of 6.7 dB.