Effect of proppant wellbore settling on proppant distribution in perforation clusters

Proppant settling in the wellbore during hydraulic fracturing operations is an important consideration as it affects the efficiency and slurry distribution in perforation clusters. This phenomenon has been studied in the past and experiments have been conducted but no field scale simulations have been performed to quantify the amount of proppant settled in different sections of the wellbore. This study focuses on utilizing critical velocity correlations available in the literature and incorporates them into a numerical simulator for simulating hydraulic fracturing stages. Comparisons have been drawn between cases where no settling was considered to cases where settling is considered to demonstrate the difference in total proppant mass entering individual fractures in different sections of the wellbore. Effects of various parameters such as injection rates, viscosity, proppant diameter, proppant density, fluid density and number of clusters (for fracturing and refracturing) have been studied. Proppant settling has been observed starting at the toe side of the stage where fluid velocity drops below the critical velocity. The settling progresses progressively towards mid clusters as the toe side clusters are plugged and the critical velocity in that region drops below a threshold value. Proppant settling is limited because as proppant deposits in a section, the flow area is reduced and this in turn increases the flow velocity to above the resuspension velocity. Ultimately the volume of proppant deposited is limited by the volume of the wellbore. The study was further expanded to include inclined wellbores. Most wells are not perfectly horizontal but rather have small angle undulations resulting in inclinations and models that account for wellbore inclination were used to compute the critical velocity. The predictions were validated using experimental data. Our study was limited to inclinations between - 9 degrees to + 9 degrees as most wellbore surveys indicate inclinations within this range. Trends indicate that proppant settling increases with upward inclination and decreases with downward inclination. The effect of settling diminishes as the hole-angle is increased or decreased. The overall change in proppant settling within the studied range of hole-angles is small (less than 7%). A comparison is also drawn for the volume occupied by proppant in various sections of the wellbore at different angles. Various design parameters that affect the amount of proppant settled are discussed in this study