Given that the conventional five-arc trajectory design of the double-step horizontal wellbore may have no feasible solution in the case of limited horizontal section spacing，this study proposed a wellbore trajectory design method based on constrained optimization. By establishing a constrained optimization model to minimize the horizontal section length，an efficient solving algorithm was constructed，which combines the quasi-analytic solution and the bisection method. Given the failure problem that the singularity polynomial of the proposed quasi-analytic solution is always zero when the inclination and azimuth angles of the two horizontal sections are the same，a modified analytical calculation formula was proposed to deal with this theoretical defect of the traditional method. Compared with the traditional iterative method，the proposed method reduces the computational complexity to the order of solving quadratic equations via the characteristic polynomial dimension reduction strategy. Examples showed that this method can converge rapidly in cases of three-dimensional stepped wells，two-dimensional wells and simplified cases. By optimizing the adjustment of the horizontal section through the bisection method，the control of the minimum trajectory length under the constraint of wellbore curvature was achieved. This method can effectively deal with the trajectory design in cases of narrow spacing，like fault-separated reservoirs，and provide theoretical support for the development of drilling software. The research findings significantly improve the reliability and engineering applicability of the trajectory design for stepped horizontal wells.

A fully coupled hydrodynamic model and field monitoring data are used to reveal the changes in in-situ stress during zipper fracturing in tight conglomerate reservoir under the volumetric development pattern of small well spacing，and the corresponding propagation pattern of fracture network. In the case that horizontal well adopts mono-interval and multi-cluster，staggered fracture arrangement and zipper fracturing，there exist stress interferences between wells and fractures at the same time. A large amount of fluid is injected into the wells fractured first to increase the pore pressure and induce the change in in-situ stress field. The mass and pressure transfer effect of fracturing improves the minimum horizontal principal stress，and reduces the two-way stress difference，which preactively creates geomechanical conditions more conducive to the formation of complex fracture network. The development effect of Mahu volumetric development demonstration zone in Junggar Basin with small well spacing shows that the stimulation effect of intervals subjected to centralized batch fracturing is much better，primary well pattern is more advantageous for the deployment of centralized fracturing and putting into production，and the wells to be fractured later have a more complex fracture network. By reducing the well spacing and conducting zipper fracturing，the horizontal stress difference is reduced continually，and the interferences between artificial fractures are mitigated，which is conducive to the formation of complex fracture network，and can effectively improve the production and recovery factor.