Wellhead gas volume control techniques in gas circulation drilling

Based on the theory of gas transient flow, a set of wellhead gas volume control theoretical models in gas circulation drill-ing are set up in combination with the formation porous flow and gas circulation drilling technique principles. According to the basic laws with which the gas flow should comply, various movement properties and dynamic pressure equalization relations of borehole fluid are illustrated, and the gas volume control method are comprehensively explained when taking gas circulation drilling technology to pen-etrate a gas zone. The Mac.Cormack method is adopted to solve the theoretical models, and numerical simulation is used to calculate and analyze the process of penetrating the gas zone. The results of study have a certain practical significance for the descriptions of dynamic process of penetrating gas zone using gas circulation drilling and the onsite application.