Anticollision-Driven Trajectory Design for Densely Spaced Multiwell Pads: A Separation-Factor Analysis of Build-Up Dogleg Severity and Inter-Well Spacing

Effective access to and stimulation of hydrocarbon reservoirs increasingly rely on combining well-architecture solutions with stimulation technologies. This study assesses directional drilling and multiwell pad systems for improving reservoir access and production, using the Śrem–Jarocin (Siedlemin) area in western Poland as a case study, and compares hydraulic fracturing with multilateral wells as complementary intensification methods. Two horizontal-well grid variants were designed in the Landmark COMPASS environment: Variant 1, a pad of twelve directional wells plus one multilateral well, and Variant 2, an adaptation of a Marcellus-type pad geometry to the local Permian sandstone reservoir. For each variant, trajectory geometry, kick-off depth, dogleg severity and horizontal-section spacing were defined, and a full anticollision analysis was performed using a magnetic measurement-while-drilling (MWD) error model and separation-factor alarm thresholds. With a kick-off depth of about 800 m and a uniform second-build dogleg severity of 7°/30 m, the required separation between closely spaced trajectories (with wellhead spacing of about 10 m) is maintained throughout drilling. Extended runs with eight build-up dogleg severity levels and four row spacings show that the minimum separation factor and uncertainty-zone clearance in the producing section scale linearly with the offset between neighboring laterals, a result confirmed by two independent series. The build-up dogleg severity leaves this margin unchanged and acts only in the kick-off interval, where it shortens the depth range of reduced separation. A row spacing of 150 m yields a minimum separation factor of 1.06, below the collision threshold; about 210 m is the practical minimum for a separation factor of 1.5 with magnetic MWD surveying.