Development of a Simplified Foam Hydraulic Model for Vertical Well Drilling

The objective of this work is to propose a simplified foam hydraulic model to be used to predict and simulate foam static and dynamic properties in spite of its simplicity, as well as adequate hole cleaning in vertical wells. Despite its simplicity, the model takes into account the real and actual conditions of the annular constituents. Thus, the analysis of the effects of the annular cuttings (drilled solids) and fluid influx are taken into account in the development of the model. If the foam flow inside the string is considered two-phase (injected liquid and gas), the annular stream is considered a three-phase fluid containing liquids (injected water, liberated water and oil from the drilled cuttings and water and oil influx from the formations), gases (injected gas, liberated gas from the drilled cuttings and gas influx from the formations) and drilled solids. Cuttings slip velocity and hindered cuttings terminal velocities are also taken into account for the adequate and accurate hole cleaning and for the analysis of the cuttings distribution profile along the vertical well. Results obtained from the proposed model revealed that foam hydraulics and rheological properties were affected by the injection pressure. The model was evaluated by running it on two foam-underbalanced wells in the Middle East with absolute average errors (on the downhole pressure at a given depth) less than 2.6 and 10.9% for the first and second wells, respectively. The model accuracy was also compared with those of other models: Valco and Economides' model and Sporker's model. The model accuracy nearly equaled that of Valco and Economides' one whereas it was less than that of Sporker.