Research On Cuttings Transport Phenomenon With Foam In Annulus Of Horizontal Wells

In recent years, with the progress of foam drilling technology, foam fluid play an increasingly important role in oil field development. Foam drilling fluid falls into the category of pseudoplastic fluid with yield values. It shows high shear force and high-viscosity under low shear rate and characteristics of strong dilution under high shear rate. These favorable rheological properties of foam fluid are beneficial to cuttings transport in well annulus, which helps to solve the cuttings bed problem. Besides, foam fluid can to some extent reduce the leakage of drilling fluid into formation, which also contributes to formation protection and hence the discovery of oil reservoir.Based on the combination of numerical simulation and simulated experiments, the effect of foam quality, annulus eccentricity, rotation of drilling pipe, and other factors on the flow properties and cuttings transport ability of foam fluid are studied with foam fluid flowing in annulus of horizontal wells. The research results on flowing characteristics of foam fluid in well annulus indicate that the density of foam decreased along the direction of foam flowing, and the change of foam's density in per meter decrease with the increase of foam quality. In eccentric annulus, velocity core of foam concentrate to the wide interval in the upside of eccentric annulus and velocity of foam decrease in the narrow part which in the underside of eccentric annulus. The study on cuttings transport ability of foam fluid shows that the cuttings transport ability of foam fluid decreases with the increase of particle diameter of cuttings and the increase of annulus eccentricity while improves with the increase of foam quality. During the study of the effect of drilling pipe rotation on flowing characteristics, it's found that the pressure difference in axial direction increases with bigger foam quality; annulus eccentricity has much influence on the offset degree and offset direction of velocity core in annulus space; with the presence of cuttings bed, the offset direction is contrary to the rotation direction of drilling pipe due to the secondary reflux of foam fluid in well annulus caused by drilling pipe rotation.The experimental study on the cuttings transport ability of foam fluid in horizontal annulus is carried out using the newly developed multi-functional equipment for simulating fluid flowing in borehole. The experiment results indicate that the critical returning velocity increases with the increase of foam quality. There exists two-order polynomial relation between critical returning velocity and foam quality. The four phases of cuttings bed breaking are observed as well as the cuttings transport characteristics of the cuttings bed.The results of numerical simulation are good agreement with the experiment. It is show that the research methods and technological paths in this paper are right. The research results have great theoretical and value to guide the foam fluid for drilling engineering design and construction.