Abstract
The parameters of gas-liquid two-phase flow bubbles in field coalbed methane (CBM) wells are of great significance for analyzing coalbed methane output, judging faults in CBM wells, and developing gas drainage and extraction processes, which stimulates an urgent need for detecting bubble parameters for CBM wells in the field. However, existing bubble detectors cannot meet the requirements of the working environments of CBM wells. Therefore, this paper reports findings on the principles of measuring the flow pattern, velocity, and volume of two-phase flow bubbles based on conductivity, from which a new bubble sensor was designed. The structural parameters and other parameters of the sensor were then computed, the “water film phenomenon” produced by the sensor was analyzed, and the appropriate materials for making the sensor were tested and selected. After the sensor was successfully devised, laboratory tests and field tests were performed, and the test results indicated that the sensor was highly reliable and could detect the flow patterns of two-phase flows, as well as the quantities, velocities, and volumes of bubbles. With a velocity measurement error of ±5% and a volume measurement error of ±7%, the sensor can meet the requirements of field use. Finally, the characteristics and deficiencies of the bubble sensor are summarized based on an analysis of the measurement errors and a comparison of existing bubble-measuring devices and the designed sensor.
Highlights
China has rich reserves of coalbed methane (CBM)
Due to the natural fracture structure of coalbeds, CBM wells need drainage and depressurization, and in that process groundwater and coalbed methane are produced from the wellbore, which results in the occurrence of gas-liquid two-phase flows in the wellbores
For vertical CBM wells, the extraction of coalbed methane is controlled by detecting and adjusting the working parameters of gas-liquid two-phase flows in the wellbores
Summary
China has rich reserves of coalbed methane (CBM). Coalbed methane buried below 2000 m covers an area of 36.81 trillion m3 , accounts for approximately 15.3% of the world’s coalbed methane reserves, and ranks as the third largest in the world [1,2]. For vertical CBM wells, the extraction of coalbed methane is controlled by detecting and adjusting the working parameters of gas-liquid two-phase flows in the wellbores. Theoretical research on two-phase flow bubbles of coalbed methane based on laboratory simulation tests is the focus of current research. The existing detection methods for the bubble parameters of two-phase flows cannot be applied to the working conditions of CBM wells. These methods include bubble detection methods based on light scattering imaging [8], the machine vision principle [9], the signal attenuation principle [10,11], tomographic imaging technology [12,13], etc
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