Effect of Well Deviation on Slurry Friction Pressures

Abstract

Abstract Increase in friction pressure with the onset of proppant stages in a hydraulic fracturing treatment is a known phenomenon. With the introduction of proppant, the hydrostatic pressure due to the column of proppant-laden slurry increases and causes a reduction in surface pressure. However, it has been consistently observed that the apparent decrease of the surface pressure is less than the value calculated on the basis of increase in hydrostatic pressure alone, indicating that the excess is due to the additional friction imparted by the solids in the slurry. When hydraulic fracturing treatments are carried out in deviated wells, the contribution of hydrostatic pressure to overall reduction of surface pressure may not be very significant, depending on the well deviation. The effect of well deviation on slurry friction is rarely reported in literature. As a result, a few correlations are available to predict slurry friction losses in deviated wells. To study the effect of inclination on proppant-laden slurry, bottom hole pressure (BHP) data are needed. Therefore, in the present study over 400 hydraulic fracturing treatments were selected, and around 100 of those with BHP data were analyzed. Results from the analyses indicated that the friction pressure observed in the slurry stages of deviated wells were significantly higher than those in vertical wells. Based on the observations, a new correlation is developed to incorporate the contribution of well deviation on slurry friction. Variables in the correlation include: proppant concentration, flow rate, tubular diameter and angle of deviation. The developed correlation was then used to predict proppant friction in other wells, which were not considered in the study. The correlation predictions were also compared with other correlations currently used in the industry. The comparison shows a better prediction from the developed correlation. The correlation is easy to use and is being incorporated into the fracturing treatment simulator for field usage.