Horizontal Well Design Optimization in Tight Reservoirs

Abstract Tight reservoirs pose significant challenges to drilling and completions and are often developed with horizontal wells and hydraulic fracturing stimulations. Designing well trajectory plans for horizontal wells needs to consider the risks of low rate of penetration (ROP) and wellbore instability while drilling, hydraulic fracture geometry and fracture conductivity while designing completions, and the risks of solids production while producing hydrocarbon from the wells. This paper aims to provide an integrated horizontal well orientation design method with various considerations during drilling, completion, and production stages. ROP is influenced by various formation properties, drilling conditions, and bit parameters. Predicting ROP within a 3D model offers a valuable opportunity to place wells in the most drillable rock. We will explain our method of 3D ROP prediction and how the predicted ROP can be used for optimizing well trajectory design. Based on analytical equations, we explain how the well's azimuth angles affect the risks of wellbore instability in both drilling and production stages of horizontal wells and the criteria for determining the most stable wellbore and perforation orientations in different stress regimes. Hydraulic fracture geometry and conductivity are related to wellbore trajectory, in-situ stresses, rock fabric, and mechanical properties of horizontal wells. Optimized well trajectory can improve hydraulic fracture geometry and dimensionless fracture conductivity while reducing near-wellbore tortuosity. Wellbore trajectory requirements for achieving optimum hydraulic fracture geometry and stimulation results will be explained. A case study is provided to illustrate the integrated process of well trajectory optimization considering ROP, wellbore instability, solids production, and hydraulic fracture geometry. In the case study, two horizontal wells were planned in the same reservoir zone. In-situ stress data was used to determine the well orientation in which the wellbores are most stable while drilling and the perforations are most stable while producing. The 3D ROP model was used to optimize drilling performance. The final optimum well trajectories were determined considering wellbore and perforation stability, drilling performance, and hydraulic fracture geometry. The drilling results validated the integrated approach for selecting the optimum horizontal well orientation.