Several recent studies have found that proppant transport in the wellbore and through perforations plays a crucial role in ensuring uniform treatment distribution among all clusters in a plug-and-perf completion. Since most portions of a horizontal wellbore are undulating and not perfectly horizontal it is important to understand how proppants are transported in deviated wellbores. The objective of this study is to evaluate the effect of wellbore inclination on proppant transport in the wellbore and into perforation clusters.
Proppant transport through a perforation in a deviated wellbore was simulated by coupling computational fluid dynamics with a discrete element method (CFD-DEM). The wellbore inclination angle ranges from 0 (downward flow in a vertical wellbore) to 180 degrees (upward flow in a vertical wellbore), and three perforation orientations (high, low and side) are considered. A proppant transport efficiency (PTE) is defined to quantify the distribution of proppant into each perforation. The results for different well inclinations are compared with experimental data for validation. The validated model is then used to show the impact of well inclination on proppant placement.
Our results show that the effect of wellbore inclination on proppant placement varies for different perforation orientations. The wellbore inclination has a small effect for a side perforation. For low/high-side perforations, the corresponding proppant transport efficiency first increases/decreases when inclination angle increases from 0 to around 90 degrees (horizontal wellbore) and then decreases/increases when inclination angle further increases. Increasing wellbore flow rate, proppant concentration, fluid viscosity, or decreasing proppant size, proppant density reduces the impact of wellbore inclination. Simulation results also show that PTE reaches a maximum/minimum value when the well inclination is between 80 and 100 degrees for low/high-side perforations. The difference between proppant transport in a horizontal wellbore and a slightly deviated wellbore can be over 20% for low flow rates (< 2 bbl/min) and as low as 5% for high flow rates (> 40 bbl/min). This indicates that proppant inertia dominates proppant transport behavior in the heel-side clusters. The situation is reversed for toe- side clusters where inclination can play a crucial role in determining proppant transport into perforations. In addition, the effect of wellbore inclination becomes much more pronounced during a refracturing operation, where a large number of perforation clusters are open to flow.
This paper presents a novel method and new results to elucidate the effects of treatment design and wellbore inclination on proppant transport into perforation clusters. Results from this study provide a way for a completion engineer to use wellbore trajectory and treatment design information to estimate the distribution of proppant into each perforation cluster in fracturing and refracturing operations.