Research on reducing fluid column pressure by injecting nitrogen in radial horizontal well

In order to improve the hydraulic breaking rock ability and sand carrying effect in radial horizontal well, based on the multiphase flow theory, underbalanced drilling technology was introduced into the design and drilling of new type radial horizontal well by using the basic principle of underbalanced drilling. Research on the pressure control during construction was conducted, and physical model and two phase (gas-liquid) flow model were established to calculate and analyze the relationships and rules of the amount of gas injection and wellbore pressure of radial horizontal well In the process of construction. As conclusion, nitrogen injecting can effectively decrease bottom hole pressure (BHP), and drilling fluid mixed nitrogen could help carrying rock fragments flow back to ground; BHP not only related with gas injection speed but also related with the flow rate of base fluid, which means that higher gas injection speed and smaller fluid rate greatly reduce BHP; annular cuttings with appropriate gas injection rate will carry out of the ground only if the drilling fluid volume reaches a certain value. This conclusion will provide a theoretical basis for construction design of new type radial horizontal well.