High-pressure, high-temperature fractured shale reservoirs are types of unconventional reservoirs that need proper drilling operations for adequate efficiency. Proper measurement of drilling fluid’s rheological properties is of importance for drilling operations that may increase the penetration rate on the one hand with proper design. Therefore, the success of drilling operations strongly depends on the proper design of drilling fluids. In this paper, we experimentally investigated the effect of potassium and sodium formate fluid on the rheological properties of drilling fluid for fractured shale core samples. The yield point and apparent viscosity for muds consisted of cellulose polyanionic and cellulose polyanionic-ultralow polymers higher than base muds. It indicates the effect of formate salts in increasing thermal stability. In addition, in polymer-based muds, more amounts of formate salts have been used, indicating the low fluid loss volume. Consequently, the shale recovery rate for potassium formate fluids is higher than sodium formate fluid.

In the paper, a shale inhibitor, glucose graft copolyammonium (GGPA), was prepared and evaluated by bentonite linear expansion test, anti-swelling experiments, mud ball experiments. The drilling...

Engineering practices employ sealing materials such as rigid bridge plugs, cementation, and polymer gels to address leaking formations; however, each has limitations: particulate-based materials rely on a match between particle size and fracture width, while chemical cementation is constrained by temperature. Although polymer gels combine elasticity with filling capacity, conventional gels have a fixed crosslinked network prone to microcracking and volume loss under sudden load changes and high temperatures. This has prompted researchers to introduce self-healing gels with reversible crosslinking characteristics; yet, under extreme deep-well conditions, simultaneously achieving high mechanical strength, self-healing, and sufficient pressure-bearing capacity remains challenging. This study synthesized a self-healing gel through dynamic covalent crosslinking. High-temperature, high-pressure tests showed that a 5% gel achieved a burst pressure of 10 MPa at 120 °C. In cyclic tensile tests, the intact gel at 200% strain showed 37 kPa, whereas for gels lacking acrylamide or tannic acid components, the stress dropped to 5 kPa or lower, confirming that the crosslinked network confers excellent tensile properties and repeatable self-healing capability. In rheological experiments, after aging at 180 °C, the storage modulus (G’) of the gel remains at approximately 1000 Pa, maintaining its gel state and possessing high-temperature sealing potential. This gel offers a novel solution for sealing drilling leaks.

To address the susceptibility of premium threaded connections in deepwater gas production strings to fretting wear and seal failure under long-term cyclic loading, a numerical simulation method for fretting wear was developed based on the Archard wear model. A UMESHMOTION wear subroutine was written in Fortran and combined with ALE adaptive technique. This approach dynamically updated the seal surface profile and accumulated the wear depth. A correlation formula relating the main seal surface contact pressure to the structural parameters was derived based on thick-walled cylinder theory. The influence of the main seal taper angle and the torque shoulder reverse angle on the sealing performance was systematically investigated via orthogonal tests combined with range analysis and analysis of variance (ANOVA). A multi-objective comprehensive evaluation model using the Analytic Hierarchy Process (AHP) was then built. The model considered sealing performance, mechanical safety, and wear resistance and selected the optimal combination of structural parameters. The results show the following: When the main seal taper angle increased from 5° to 20°, the wear depth first decreased and then increased, while the contact pressure first rose and then dropped. The main seal contact pressure peaks at 882 MPa at a main seal taper angle of 15°. The Von Mises stress in the connection decreased monotonically. The main seal contact pressure and the seal index increased monotonically with the torque shoulder reverse angle, whereas the torque shoulder contact pressure showed a V-shaped change. The torque shoulder reverse angle significantly influenced the sealing performance and was the main factor. Considering the three performance aspects, the optimal combination was a main seal taper angle of 15° and a torque shoulder reverse angle of 15°. These results provide a theoretical reference and technical support for designing anti-fretting structures, improving sealing performance, and guiding field selection of premium threaded connections under deepwater gas well conditions.