The formation of nano-micropore fractures in the Mahu well area of Xinjiang is developed, and the phenomenon of collapse and leakage in the same layer occurs many times, which leads to serious wellbore instability and seriously affects the drilling process. In this paper, 2-acrylamide-2-methylpropanesulfonic acid, polyvinyl pyrrolidone and dimethyl diallyl ammonium chloride were grafted onto the surface of mSiO₂ by aqueous solution polymerization with KH570 modified nano-silica as the ‘core’. A self-adaptive strong plugging agent with high temperature resistance was prepared. The experimental results show that the morphology of XZ-APA is spherical, and the size is between 40 nm and 135 nm. The particle size of XZ-APA expanded adaptively with changes of temperature and concentration. When the temperature increased from 25 ℃ to 65 ℃, the D₅₀ expanded from 124 nm to 805 nm. When the concentration increases from 0.1 g/L to 10 g/L, the D₅₀ expands from 105 nm to 3.2 μm, reaching micron level, which can realize multi-stage plugging of nano-microporous fractured formations. In the sand bed experiment, 3% XZ-APA reduced the leakage of 40~60 mesh and 60~80 mesh sand beds from 119 mL and 128 mL to 29 mL and 25 mL. In the pressure transfer experiment, 3% XZ-APA also has a good plugging effect on the core from the Mahu well area, and the pressure transfer rate is reduced by more than 72%. By adding 2% XZ-APA to the drilling fluid system, the leakage of the 40~60 mesh sand bed can be reduced from 3.2 mL to 1.2 mL, and the pressure bearing capacity can be more than 6 MPa. The leakage of the 20~40 mesh sand bed is reduced from 300 mL to 44 mL, and the pressure bearing capacity is increased from 1 MPa to more than 6 MPa, indicating that XZ-APA can be effectively blocked in WBDFs and improve the pressure bearing capacity. At the same time, its plugging effect is better than that of conventional plugging materials (such as asphalt), and can be used in combination with conventional plugging materials to achieve a better plugging effect. In this paper, XZ-APA is used as the core treatment agent to form a set of water-based drilling fluid systems with high temperature resistance and self-adaptive strong plugging suitable for the Mahu well area, which is helpful to solve the problem of wellbore instability caused by filtrate invasion in the Mahu well area.

With increasing drilling depth and large dosage of weighting materials, drilling fluids with high solid content are characterized by poor stability, high viscosity, large water loss, and thick mud cake, easier leading to reservoir damage and wellbore instability. In this paper, micronized barite (MB) was modified (mMB) by grafting with hydrophilic polymer onto the surface through the free radical polymerization to displace conventional API barite partly. The suspension stability of water-based drilling fluids (WBDFs) weighted with API barite:mMB = 2:1 in 600 g was significantly enhanced compared with that with API barite/WBDFs, exhibiting the static sag factor within 0.54 and the whole stability index of 2. The viscosity and yield point reached the minimum, with a reduction of more than 40% compared with API barite only at the same density. Through multi-stage filling and dense accumulation of weighting materials and clays, filtration loss was decreased, mud cake quality was improved, and simultaneously it had great reservoir protection performance, and the permeability recovery rate reached 87%. In addition, it also effectively improved the lubricity of WBDFs. The sticking coefficient of mud cake was reduced by 53.4%, and the friction coefficient was 0.2603. Therefore, mMB can serve as a versatile additive to control the density, rheology, filtration, and stability of WBDFs weighted with API barite, thus regulating comprehensive performance and achieving reservoir protection capacity. This work opened up a new path for the productive drilling of extremely deep and intricate wells by providing an efficient method for managing the performance of high-density WBDFs.

A low-cost eco-friendly aqueous foam, especially the robust foam with great tolerance to high salinity and high temperature, is in great demand in the oil industry, e.g., oil and gas well or geothermal well drilling. Herein, an ultra-stable aqueous foam was developed using the biodegradable cellulose microfiber (CMF) as a foam stabilizer. The foam stabilized by CMF shows excellent tolerance to the high concentration of NaCl (6.0 wt%) and CaCl₂ (0.25 wt%) and the related drainage half-life times (T_0.5) reach 1750 and 2340 s respectively. By contrast, the foams without CMF are completely drained (T_0.5 = 0 s) when NaCl concentration is greater than 6.0 wt% or CaCl₂ concentration is greater than 0.20 wt%. Notably, T_0.5 of the foams stabilized by CMF at these saline concentrations still can maintain above 1000 s even after aging at 120 ℃ for 16 h, exhibiting an outstanding foam-stabilizing performance at high temperature. Experimental results suggest that the salt and high-temperature tolerance of CMF in foam stabilization is attributed to the electrically uncharged surfaces, the formation of a gel-like structure and the excellent thermal stability. This work not only provides a promising candidate of aqueous foam stabilizer to deal with high temperature and high salinity but also presents a natural-based solution for an environmentally friendly drilling industry in the future.