The tight oil reservoir rocks in the Jidong Oilfield are generally characterized by high hardness, strong abrasiveness, and extremely unevenness, which seriously reduce the drilling efficiency. In view of this problem, the mineral composition, hardness, plasticity coefficient, and drillability of rocks were first determined. It was found that the rock integrity, compactness and high hardness are the main factors leading to the low rock breaking efficiency of PDC bits. Then, combined with logging data, the drilling resistance profile of the whole well section was established. According to the crushing mechanism of rocks under the action of a PDC bit, the mechanical model of a single composite plate under rock crushing conditions is established, and the influence of the back angle on the cutting force is analyzed. The flow field distribution of the drill bit surface under different nozzle combinations was calculated by finite element numerical simulation. Based on the experimental and simulation results, the optimal backward angle was 15°, and the optimal nozzle combination was two 16-mm central nozzles and five 14-mm peripheral nozzles. Finally, a personalized PDC bit design scheme for tight oil reservoirs in the Jidong Oilfield was proposed. The scheme includes the following: (1) a 5-blade straight-arc crown is profiled; (2) anti-impact cylindrical components are set; (3) the nozzle hydraulic structure adopts a bending type; and (4) the diameter-retaining teeth and diversion grooves are optimized. The optimized bit reduces stick–slip, improves stability, and has an obvious acceleration effect.

Wellbore instability is the primary technical problem that restricts the low-cost drilling of long-interval horizontal wells in the shale formation of the Jidong Oilfield. Based on the evaluation of the mineral composition, structure and physicochemical properties of shale, this paper investigates the mechanical behavior and instability characteristics of shale under fluid action by combining theoretical analysis, experimental evaluation and numerical simulation. Due to the existence of shale bedding and microcracks, the strength of shale deteriorates after soaking in drilling fluid. The conductivity of the weak surface of shale is much higher than that of the rock matrix. The penetration of drilling fluid into the formation along the weak surface directly reduces the strength of the structural surface of shale, which is prone to wellbore collapse. The collapse pressure of the shale formation in the Nanpu block of the Jidong oilfield was calculated. The well inclination angle, azimuth angle and drilling fluid soaking time were substituted in the deterioration model of rock mechanics parameters, and the safe drilling fluid density of the target layer was given. This work has important guiding significance for realizing wellbore stability and safe drilling of hard brittle shale in the Jidong Oilfield.

The shale oil horizontal wells in the Songliao Basin are affected by a lack of mature theories, technologies and experiences in the direction of wellbore stability. Wellbore collapse may occur, and in severe cases, the wellbore may be scrapped, resulting in huge economic losses. Therefore, aiming at addressing the above problems, rock mechanics experiments were carried out. Based on the theories of elasticity and rock mechanics, this paper considers not only the influence of the bedding plane, but also the influence of hydration on the strength weakening of the shale body and the bedding plane. The analysis shows that no matter under which in situ stress mechanism, the wellbore in the vertical well section is the most stable, and when the inclination angle is approximately 45°, the wellbore is most likely to be unstable. Changes in water content do not affect the most stable or unstable regions. Under the same conditions, the equivalent density of collapse pressure increases with the increase in water content. In addition, field examples are also analyzed to verify the accuracy of this model, which can provide a theoretical and technical basis for the safe construction of continental shale oil horizontal wells.

The rock abrasiveness is determined with various methods, which results in no uniform standard formed. In order to predict the PDC bit wear and the abrasiveness of complex strata, the force analysis of the PDC broken rock was carried out, and the bit axial load and torque were obtained, respectively. Then, the calculation model of PDC special energy consumption is deduced. Combining the typical distribution patterns of different strata, the specific energy prediction model of complex strata is established. The wear coefficient of PDC is obtained by the relationship between the triaxial compressive strength of rock and the specific energy of rock breaking, and the grading coefficient and grading standard of abrasiveness of the composite formation are derived, which led to the grading coefficient and grading standard of complex strata abrasiveness. The field test of a well in the north of Songliao Basin verified the rationality and effectiveness of the abrasiveness grading standards and provided the basis for the selection and design of the bit.

The channeling of CO₂ gas is affected by the development of reservoir fractures. In order to improve the gas injection effect, the finite element numerical analysis software Comsol Multiphysics combined with the fluid–solid coupling theory was used to establish the three-dimensional geological model of the Hailar Bei 14 block, and the geostress of the study block was inverted. According to the failure criterion of rocks, the natural fractures of the block are predicted, and the distribution characteristics of artificial fractures are obtained by combining the fracturing situation and fracturing time sequence. Based on the simulation of the pressure field and flow field distribution of the Bei 14, the main effect of the fractures on the gas injection is revealed. The reason of the gas channeling in the Bei 14-X51-59 well is analyzed, which provides an important basis for the formulation of the CO₂ flooding scheme.

This study focuses on the transportation of non-uniform cuttings in the drilling process of long-reach horizontal wells, conducting a comprehensive theoretical analysis and experimental investigation. Initially, a computational model was established to analyze the influence of cuttings size distribution, fluid dynamics parameters, and wellbore geometry on the transport of non-uniform cuttings. The research elucidates the non-linear relationship between cuttings transport efficiency and parameters such as flow velocity, well inclination, and drill pipe rotation rate in long-reach horizontal wells. It also identifies the existence of a critical flow velocity, beyond which drilling fluid can effectively carry cuttings, preventing their accumulation at the well bottom, and ensuring wellbore cleanliness. Additionally, the paper proposes optimization strategies for wellbore cleaning based on the transport behavior of cuttings, including adjustments to fluid flow velocity and optimization of well inclination, aimed at enhancing drilling efficiency and reducing drilling costs. The findings provide theoretical guidance for cuttings management in long-reach horizontal wells, contributing to improved safety and cost-effectiveness in drilling operations. They hold significant value for advancing the technology of drilling horizontal wells under complex geological conditions.