The Optimization Of Gas Injection Volume For Air Drilling

As the the vanguard of Underbalanced drilling, air drilling is the most economical method. It has the merits that include fast drilling speed and the protection for gas producing formation. But as air drilling is applying extensively , many difficult conditions has arisen, including the difficulty of the gas taking crumbs, the jam of the borehole, the buckling of the sidewall, the blast of the downhole and so on. One of the keys to solve the questions is the definition of the minimum gas volume. The lower gas injection volume is,the more difficultly drill cuttings are carried, furthermore,the drill will be stuck. On the contrary, if gas injection volume is higher, the washout to the drill hole will be on the high side, and the financial burden will be increased. Therefore, it is important to research the minimum gas injection volume.This paper makes the research that uses method combined theory with numerical simulations. Through lots of research, it introduces the development of the air drilling at home and abroad, arises the purpose and the significant; makes a systematic analysis for the air drilling according to the GUO model, deduces the temperature distribution of the wellbore from the correction model of the Grounding Resistance, the heat that be caused from the friction of fluid and the balance equation. And in accordance with it to consider the eccentric of the Drill String revolving, correct the model of the gas injection volume based on the GUO model; using the Fluent6.3.26, it makes a numerical simulation to experimental model and the surface of discontinuity of the wellbore and gets the distribution of the Flow Field of the wellbore annulus and the influence which the parameters exercise on it. Besides, it verifies the reliability of the Numerical simulations according to experiment and the theory computation. According to the scene data, it uses the correction model to compute to verify the accuracy of the model.