Wellbore instability caused by the dispersion of the clay is one of the most important challenges in drilling operation of fractured formations. The synthesis of new plugging inhibitors and the research of drilling fluid systems are key steps to keep the wellbore stabilization. In this paper, the limitations of conventional drilling fluid inhibitors are discussed and a new plugging inhibitor PAS-5 is synthesized by using amine inhibitor, polyethylene glycol and asbestos fiber as the main monomers. The detailed synthesis step of the plugging inhibitor PAS-5 is illustrated and its action mechanism is explained by scanning electron microscopy. In order to express the good effect of the PAS-5, a new evaluation system is used to indicate its plugging performance. At the same time, the plugging inhibitor PAS-5 was used on-site drilling operation in the Ordos Basin. The results of research show that the synthesis process of PAS-5 is simple and the effect of plugging inhibition is obvious. Compared with conventional treatment agents? PAS-5 outperforms sulfonated asphalt FT-1 and emulsified asphalt RHJ-3 in terms of plugging inhibition performance, with a plugging rate of 90.5% and roller recovery rate of 93.7%. It also has better temperature resistance, there is almost no change in viscosity and filtrate loss when the temperature rises from room temperature to 80°C. The field application results indicated that PAS-5 meets the requirements of drilling, that the reaming time of the trips of the wells is shortened considerably, that the ROP is improved, and that the hole enlargement rate is less than 6%. During the drilling process, PAS-5 can inhibit formation hydration and seal small cracks, thus maintaining the stability of the borehole. This study synthesized a novel plugging inhibitor PAS-5 and an evaluation system was adopted to reveal its plugging performance, and achieved good application effect in on-site drilling operations.
Previous studies have established that the selection of gas extraction borehole parameters is crucial for the effectiveness of gas extraction. To more accurately determine the reasonable extraction radius of gas extraction boreholes in the coal seam, this study was based on the actual occurrence conditions of the coal body. A coal-seam gas-seepage model, considering dynamic changes in permeability under gas–solid coupling conditions, was constructed. It was combined with FLAC3D numerical simulations to develop a borehole extraction model closer to the field’s natural needs. The study revealed the influence of borehole diameter and spacing on gas extraction, obtained the radius of effect of borehole extraction, and optimized the gas extraction borehole parameters based on data simulation experiments. Multiple sets of experimental results indicated that the optimal parameters are a borehole diameter of φ = 113 mm and a borehole spacing of 5 m. Applying these parameters in on-site tests at the 14,303 working faces of a particular mine significantly improved gas extraction efficiency, with a 29.7% increase in gas extraction concentration. This verified the accuracy of the simulation results and provides a scientific basis for cost reduction and efficiency enhancement in wellbore mining.
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