A novel shale inhibitor was synthesized by free radical copolymerization in aqueous solution, using acrylic acid (AA), acrylamide (AM), maleic anhydride (MA) KH-570 as reaction monomers and potassium persulfate as initiator. The structure of the copolymer was characterized by Fourier transform infrared spectroscopy (FT-IR). Thermogravimetric analysis (TGA) showed that the thermal decomposition temperature of the copolymer was higher than 226°C, which indicated that the copolymer had good high temperature resistance. At the same time, the inhibition performance of the copolymer was further evaluated by linear expansion, immersion test and rolling recovery. The experimental results show that the inhibition performance of organosilicon polymer is obviously better than that of potassium chloride (KCl) and potassium polyacrylate (KPAM), and it can be used as an inhibitor in shale gas drilling.

Wellbore instability and formation collapse are crucial issues in the process of well excavation in the oil industry under extreme high temperature conditions. A novel zwitterionic quaternary copolymer (PDANV) of 4-vinylpyridine (VP), N, N-dimethylacrylamide (DMAA), 2-acrylamido-2-methylpropane sulfonic acid, N-vinylcaprolactam (NVCL) was synthesized in aqueous solution by free radical copolymerization reaction. The structure of PDANV was characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (1 H NMR), and the results indicated that ideal product are obtained. Thermal stability of PDANV was revealed by thermogravimetric analysis (TGA) and result showed that thermal degradation of PDANV mainly happened over 301°C. Simultaneously, PDANV was prepared to further evaluate its effect on rheological and filtration properties of water-based drilling fluids (WBDFs). The results showed that the fluid loss (FL_API) of PDANV/WBDFs was only 3.4 mL, 6.0 mL before and after hot rolling at 260°C for 16 h, respectively. Compared with the 19.2% and 57.9% reduction of traditional fluid-loss additives CMC and Driscal, the fluid-loss reduction rate of PDANV/WBDFs was 87.5% in ultra-high temperature environment. Additionally, PDANV performed satisfactorily with great properties in WBDFs even at high concentration of salts and calcium. Therefore, it can be used for applications where the PDANV is subjected to certain harsh environments, such as extreme salinity and ultra-high temperature conditions.

Drilling fluid losses into formation voids are among the major issues that lead to increases in the costs and nonproductive time of operations. Lost circulation materials have been widely used to stop or mitigate losses. In most cases, the size of the loss zone is not known, making conventional lost circulation materials unsuitable for plugging the loss zone. In this study, novel temperature-sensitive LCM (TS-LCM) particles composed of diglycidyl ether of bisphenol A (DGEBA) and 4,4′-diaminodiphenyl methane were prepared. It is a thermal-response shape-memory polymer. The molecular structure was analyzed by Fourier transform infrared spectroscopy. The glass transition temperature (T_g) was tested by Different scanning calorimetry (DSC). The shape-memory properties were evaluated by a bend-recovery test instrument. The expansion and mechanical properties of particles were investigated under high temperature and high pressure. Fracture sealing testing apparatus was used to evaluate sealing performance. The mechanism of sealing fracture was discussed. Research results indicated that the T_g of the TS-LCM was 70.24 °C. The shape fixation ratio was more than 99% at room temperature, and the shape recovery ratio was 100% above the T_g. The particle was flaky before activation. It expanded to a cube shape, and the thickness increased when activated. The rate of particle size increase for D90 was more than 60% under 120 °C and 20 MPa. The activated TS-LCM particles had high crush strength. The expansion of the TS-LCM particles could self-adaptively bridge and seal the fracture without knowing the width. The addition of TS-LCM particles could seal the tapered slot with entrance widths of 2 mm, 3 mm and 4 mm without changing the lost circulation material formulation. The developed TS-LCM has good compatibility with local saltwater-based drilling fluid. In field tests in the Yan’an area of the Ordos Basin, 15 shale oil horizontal wells were plugged with excellent results. The equivalent circulating density of drilling fluid leakage increased by an average of 0.35 g/cm³, and the success rate of plugging malignant leakage increased from 32% to 82.5%. The drilling cycle was shortened by an average of 14.3%, and the effect of enhancing the pressure-bearing capacity of the well wall was significant. The prepared TS-LCM could cure fluid loss in a fractured formation efficiently. It has good prospects for promotion.

As a washing medium, the drilling fluid is used to clean the hole in the process of drilling. Weighting material such as barite, iron-ore fines used for the preparation of high-density water based drilling fluid because of its high density and well wettability. However, the rheological performance is distinctly of vary types, sizes weighting materials for high-density drilling fluid. For controlling and maintenance of the rheological properties of high-density drilling fluid system, adding barite and iron-ore powder with different particle size into water based drilling fluids increasing the material density to 2.30g/cm3, obtained the viscosity effect which is defined as the variation of apparent viscosity after the drilling fluid rolling 24hours at high temperature (180°C), then analysis of its mechanism of action. The results show that, it is easy to forming strong particles as the core of the rules of the tentacles spherical structure with 250-350 mesh iron-ore powder to weight the water based drilling fluid, which could keep the stable rheological properties and make the size of solid particles integrated with the drilling fluid system closely not only holding the minimum viscosity effect also maintaining the best sedimentation stability. Similarly, 200-250 mesh barite perform the appropriate viscosity of water based drilling fluid and maintain a good sedimentation stability, and the maximum value viscosity effect is adding the 325 mesh barite.