APPLICATION OF A SPECIAL TECHNIQUE FOR CONTROLLING THE CUTTING BED HEIGHT IN GAS DRILLING OF HORIZONTAL WELLS

Sedimentation of cuttings limits application of gas drilling through a horizontal well section. We have constructed a theoretical model of two-layer flow as applied to flow of the gas and solid particles; we have developed a diffusion theory for gas drilling conditions for horizontal well sections. The calculations are performed using data from real wells. The calculations show that when drilling a horizontal section, a cutting bed will inevitably be formed and we need to control sedimentation of the cuttings by regulating the gas flow velocity. For low gas velocities, the resistance of the particles to motion is mainly created as a result of their collisions with the well wall in the cutting bed zone. For high gas flow velocities, the major resistance is created as a result of collisions of the particles with the well wall in the two-layer flow zone. Based on previous studies of two-layer flow and the cutting bed, it was established that gas injection should be done at the bottom of the well when gas drilling a horizontal section. The ascending gas flow velocity should be 1.5 times higher than the particle sedimentation rate. Only under such conditions is control of cutting bed formation possible.