A new hole cleaning criteria for drilling operations of oil wells

A study of drilling fluid flow in the annular space and drill pipe through residence time distribution (RTD) analysis of a tracer injected in impulse form while drilling an oil well is presented in this article. Two field trials were carried out in order to evaluate the technical feasibility and potential practical application of the RTD theory and the dispersion model. From the results it is possible to explain physically the flow behavior and its relation with parameters such as carrying capacity of the drilling fluid and hole cleaning conditions. The RTD analysis of tracer response indicates the presence of anomalous flow in both trials, characterized by two fluid volume fractions traveling with different velocities. The magnitude of these volume fractions concerns directly with the carrying capacity of the drilling fluid, hence, the hole cleaning conditions as is explained along he work. The dispersion number (RDN) as well as other distribution functions are suggested as a measure of the overall behavior of the fluid in a hole. This criterion is compared with empirical correlations employed in the industrial practice.