Numerical Simulation And Parameter Optimization Of Cuttings Transportation In CBM Horizontal Well

Coalbed methane(CBM), with its huge resource advantage and broad business prospects, especially in energy, environmental protection and administration of coal mine safety aspects shown in the important strategic value, has caused wide public concern. CBM horizontal well technology, which has been increasingly used in CBM development, is not only with a low cost, but also can bring a high yield. However, with the characteristics of "brittle", the coal seam often causes many safety problems in the CBM drilling construction. These problems include sticking, suppress pump, cuttings transport jam, hole collapse and other complex situation. Therefore, the maintenance of hole cleaning is the key to conduct drilling construction successfully.Based on the above situation, a variety of related literature about the CBM horizontal well drilling technology and cuttings transports domestic and abroad are studied. At the same time,the research status is summarized. Secondly, on the basis of previous work, considering the rotation of the drill string and particle inter-atomic forces influence on cuttings transports, cuttings transports force model is modified and the critical speed and cutting roll cuttings suspension critical velocity model are established. Then the index and method of the carrying cuttings effect is summarized. Again, using CFD software and choosing Eulerian two-phase flow model, experiments and analysis show that the model can simulate the cuttings transports status. And then, using numerical simulation method, considering drilling tool rotation, the influence of drilling fluid flow and carrying transports about drilling fluid flow, drilling fluid viscosity, drilling tool rotation speed, eccentricity and cuttings particle size are analyzed. Finally, physical model is built based on the field well example. Considering the construction requirements of well drilling, the diameter, tilt Angle and the down position of the concentric casing section gas injection nipple are optimized. Cutting-carrying effects under the different condition of cycle medium are analyzed. At the same time, the concentric casing drilling and conventional drilling theories and results are analyzed. The results show that when the nozzle laid down to the horizontal section, cuttings transports is better than vertical section and bending section; under concentric sleeve auxiliary drilling process, the drilling fluid with cuttings transports is better than using water; concentric casing drilling technology can effectively improve the cuttings transports ability; carrying cuttings effect is superior to the conventional drilling technology.