METHOD FOR DETERMINING EFFECTIVE GAS DRAINAGE RADIUS BASED ON SF6 FLOW FIELD DISTRIBUTION

摘要

The effective gas drainage radius of a borehole is a basic parameter of coalbed gas drainage directly relating to pre-draining time and the maximum permissible gas pressure, and is an important basis for determination of drainage borehole spacing.To address the problems of existing determination method such as difficult field operation and poor practicability, a method for determining the effective gas drainage radius of a borehole was proposed on the basis of the radial steady-state flow model for tracer gas SF6 and coalbed gas.The determination conditions of radial steady-state flow field were created through field layout of aeration holes and drainage observation holes, the time of observing SF6 from drainage observation holes and aeration holes at variable spacing was recorded, thereby flow field spreading scopes of different gases and their corresponding time points were determined.And by the law of gas pressure distribution within flow field and according to the maximum permissible gas pressure, the effective gas drainage radii at different time points were determined, so as to obtain the relationship between effective gas drainage radius of coalbed borehole and pre-draining time, which offers the basis for design of drainage boreholes and improves coalbed gas drainage effect.