Comparison of Heterogeneously-Propped Hydraulic Fractures for Vertical and Lateral Wells
Abstract:Heterogeneous proppant placement (HPP) technologies offer improved hydraulic fracturing performance through the creation of channels within propped fractures (see figure). Such schemes, however, can suffer from reduced performance due to uncertainty in reservoir properties (e.g.: embedment and moduli). This is particularly true of unconventional reservoirs where properties can be highly heterogeneous. We demonstrate that the mechanisms controlling uncertainty in HPP performance differ between vertical and lateral wells.
For computational efficiency, we combine the boundary element method to simulate formation deformation with a detailed discretization of the proppant within the fracture to predict conductivity of the HPP channels. We performed an extensive parameter study with thousands of scenarios relevant to HPP, including placement geometries consistent with both vertical and lateral wells. Global sensitivity analysis (GSA) was then applied to quantify and rank contributions from uncertain input parameters to variance in fracture conductivity.
We were able to rigorously quantify the impact of parametric uncertainty. We found that for lateral wells the uncertainty in the conductivity is dominated by the uncertainty in diffusion of the proppant. For vertical wells, the dominant factors causing uncertainty in the performance change with stress. At low stress, performance is controlled by factors that dictate pillar geometry. At high stress, parameters that help preserve channels against closure stress control conductivity.
Our results highlight the robustness of the HPP concept and quantify the sources of uncertainty in HPP performance. Further, we can clearly identify the fundamental parameters that control HPP conductivity and reveal that they are different for wellbore geometries that are typical of unconventional wells in North America. This implies that optimal HPP strategies will differ between vertical and lateral wells.