Experimental Investigation of Transport Mechanisms of Coal Particles andGas-Water Interfacial Friction Factor for Stratified Flow in Coal-Bed MethaneHorizontal Wellbore

摘要

In coal-bed methane (CBM) horizontal wells, coal particles generally deposit on the low side of the wellboreto form a particle bed, which increases well pressure loss and even blocks the well. The coal particle bedundergoes changes in height and geometry with the fluctuation of gas and water production. Besides, with alow water flow rate, the water layer in CBM well is extremely thin. Both the dynamically changing particlebed and thin water layer make the conventional gas/water interfacial friction factor (fi) prediction methodfor stratified flow in horizontal pipe not suitable for that of CBM well. Based on the large-size multiphase complex flow experimental equipment, a gas/liquid/solid three- phaseflow experiment in horizontal pipe was carried out. In the experiment, gas flow rate, water flow rateand coal particle size were the three main factors considered. During the experiment, the gas/water flowpattern, migration of coal particles and evolution of blocked section could be investigated through thetransparent pipe. Furthermore, due to the significant effect of coal particle bed on the height of gas-waterinterface, a non-negligible gravitational pressure drop calculated using water level differences is taken intoconsideration when obtaining the friction pressure drop.