On cutting transport for air reverse circulation in horizontal and inclined wells

Air reverse circulation (RC) drilling has drawn considerable interest and has been adopted in tunnel drilling owing to its beneficial features. Cutting transport is a primary concern in RC drilling because poor cutting transport efficiency may lead to several problems, such as stuck pipes, excessive torque and drag, and severe bit wear. The Euler-Euler method of computational fluid dynamics simulation was applied to model the gas-solid two-phase flow in a drill pipe to determine the influence of various parameters on cutting transport. The effects of the air velocity, cutting concentration, rate of penetration (ROP), particle diameter, and inclination angle were investigated by analyzing the variation in the pressure drop, characteristics of cutting motion, and efficiency of cutting transport. The results revealed that the positive contribution of air velocity to transport efficiency was restricted. The optimal concentration of cuttings was approximately 20 %. The pressure drop, average volume fraction, and cutting migration ratio tended to be positively correlated with the ROP. An increase in the cutting diameter led to a decrease in transport efficiency. At an inclination of 30 degrees, the least cutting transport efficiency was observed.