Summary Under the three-layer 3D development mode of shale gas reservoirs, the continuous increase in well pattern and fracture network density poses severe challenges to the trajectory design of the infill well. Existing design methods exhibit significant shortcomings: Traditional anticollision models only consider geometric wellbore avoidance, overlooking the geological obstacle of the fracturing effect domain, while, existing fracturing-interference models suffer from excessive geometric simplification, leading to overly conservative risk assessments that severely constrain efficient drilling. To address these deficiencies, we propose an innovative theory and methodology for optimizing infill well trajectory design. First, at the modeling theory level and based on the Minkowski sum theory, we establish, for the first time, a composite ellipsoidal obstacle model that couples error ellipsoid and fracturing ellipsoid to achieve precise geometric characterization of spatial interference risks. Second, in terms of computational methods, through coordinate transformation and constrained optimization theory, we derive and solve an exact calculation model for antifracturing-interference separation factor, overcoming the limitations of traditional methods that rely on empirical formulas and conservative assumptions. Furthermore, regarding trajectory design strategy and using the industry-standard minimum curvature method, we construct a universal design model for 3D bypass trajectory, along with an optimization strategy “primarily employing two-build adjustment approach, supplemented with three-build design.” Finally, within the optimization framework and integrating the above advances, we establish an infill well trajectory optimization model with minimized drilling time as the objective and antifracturing interference as a hard constraint. Field case validation demonstrates that traditional models, employing conservative assumptions, overestimate obstacle sizes, resulting in a 70-m reduction in effective reservoir penetration and a 3.1% increase in drilling time, severely constraining development efficiency. The proposed model comprehensively accounts for the distribution characteristics of fracturing effect domain and trajectory error domain, achieving precise quantification of fracturing interference risks and significantly improving drilling efficiency and economic viability. This study provides a systematic theoretical tool and design paradigm for the safe and efficient drilling of infill wells under intensive well pattern 3D development modes.
Dou et al. (Sun,) studied this question.