Research on the Conductivity-Based Detection Principles of Bubbles in Two-Phase Flows and the Design of a Bubble Sensor for CBM Wells

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.

The Development and Test of a Sensor for Measurement of the Working Level of Gas–Liquid Two-Phase Flow in a Coalbed Methane Wellbore Annulus

“…Figure 5 shows the basic detection principle of the bubble probe. Figure 5 A shows the elementary structure of the bubble probe, and Figure 5 B shows the data process circuit of the bubble probe [ 22 ]. As shown in Figure 5 A, the bubble probe consists of a sleeve and an electrode.…”

“…The sleeve connects with the VCC (the positive pole of the power), while the electrode connects with the GND (the negative pole of the power). The test device of the conductivity is built when the power is open [ 22 ].…”

“…The gas–liquid two-phase flow can be divided into different patterns according to the angle of the pipeline where the two-phase flow is located. As the research regarding CBM wells consists in vertical ascending pipelines, the two-phase flow in a CBM well can be analyzed in terms of bubble flow, slug flow, churn flow, annular flow, and fine beam annular flow, which change as gas content increases [ 22 ], as shown in Figure 6 .…”

The Development of a Gas–Liquid Two-Phase Flow Sensor Applicable to CBM Wellbore Annulus

“…Both domestic and foreign scholars have carried out numerous studies on the conducting probe [16,17,18], and relevant theory and practice are mature. The bubble measurement principle of the bubble probe will be briefly introduced below.…”

“…Therefore, the pattern of two-phase flow can be roughly identified by judging the quantity of bubbles within a certain period. The method for pattern flow recognition aboveground and underground is to recognize and count the instances of high and low electrical levels [16]. This theory can also be used for the pattern flow’s automatic identification.…”