Drilling the mudstone of the Shihezi Formation in the Sulige Block is prone to complex issues such as lost circulation，frequent sticking and jamming during tripping，and wellbore collapse，which severely restrains the operation efficiency of drilling. To tackle the technical challenge of wellbore instability in drilling the Shihezi Formation mudstone，the mechanisms behind wellbore instability of this block were investigated by collecting samples of the Shihezi Formation mudstone and researching the microscopic fabrics and physical and chemical properties of rocks as well as the law governing the effect of hydration on rock mechanics parameters. Meanwhile，the variations of samples in the microscopic morphology，mechanical property and dispersion capability were observed after they are treated by aqueous solutions of different inhibitors and different drilling fluid systems. It was found that，on the basis of a composite salt system，the combined use of organic and inorganic inhibitors to suppress shale hydration achieved the best performance in improving wellbore stability of the Shihezi Formation mudstone. Correspondingly，countermeasures to enhance wellbore stability were proposed. The findings of this research provide theoretical support for techniques improving wellbore stability in the Sulige Block and assist in the safe，steady，and efficient development of the Sulige self-operated block.

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.

Addressing Jimsar shale oil reservoir，this study aims to enhance fracture-controlled reserves by conducting theoretical research and technical practices. Focused on four key aspects—fracture network design，construction，proppant effectiveness，and the enhancement of in-situ oil mobility，three generations of technological advancements have been realized. Fundamental theories regarding the effective propagation of hydraulic fracture in thin interlayers and key technologies such as multi-cluster fracturing within a stage and the use of cost-effective materials have been mastered. An integrated horizontal well volume fracturing technology system centered on fracture-matrix matching，precise stimulation，multi-scale proppant support，and CO₂ prepad injection has been developed. The key technical indicators of fracturing have reached the advanced domestic level，supporting the large-scale and efficient development of Jimsar shale oil. In 2023，the oil production of Jimsar shale oil surpassed 60×10⁴ t，with a consecutive annual production increase of 10×10⁴ t in the block for three years. This achievement has provided robust technical support for the establishment of China's first national continental shale oil demonstration zone by 2025 and serves as a reference for optimizing shale oil development technologies in other regions of China.

The key to breakthroughs in shale oil exploration and development lies in the characterization and prediction of reservoir bedding fractures. The complexity of its genetic mechanism and the diversity of influencing factors have led to bottlenecks in the prediction technique. Based on the identification of bedding fractures at core and thin section scale （~ mm），and evaluation of bedding fractures through resistivity imaging and at conventional logging scale （~ m），it is found that the bedding fractures in the sweet spot section of Lucaogou Formation in Jimsar Sag are the most developed in dolomite reservoirs，followed by dolomite siltstone and argillaceous siltstone. These fractures are predominantly found in the distribution area of tight reservoirs and exhibit a significant negative correlation with reservoir matrix porosity. Furthermore，combined with the lithology distribution predicted by 3D seismic data and the porosity distribution from inversion，this study investigates the technique for predicting bedding fractures in shale reservoirs by advancing sequentially through core-points，logging-lines，and seismic-surfaces using the well-seismic information scale matching technology. This method integrates the advantages of accurate core identification，high longitudinal resolution of logging curves，and strong lateral continuity of 3D seismic data. The verification conducted on 27 wells in the sweet spot section of the Lucaogou Formation in Jimsar Sag shows an average relative prediction error of 8%，indicating a satisfactory application effect. This technology can provide robust support for the exploration and development of shale oil in the Lucaogou Formation，and it also holds significant reference value for the evaluation of shale oil reservoirs in other basins.