Study on Displacement Gas Invasion Law During Horizontal Well Drilling in Fractured Gas Reservoir

When gravity displacement gas invasion occurs in fractured reservoirs, it is easy to cause blowout accidents if not handled properly. Based on ANSYS software, a model of horizontal well intersecting vertical fracture was established to simulate the phenomenon of gas-liquid displacement under formation conditions, explore the influence law of drilling fluid density, viscosity and fracture width on the size of gravity displacement window, and compare the influence of changing drilling fluid density, viscosity and applying wellhead back pressure on the gas influx rate and loss rate during gravity displacement. And the following research results are obtained. First, after the intrusive gas enters the vertical well section, the gas migration rate increases and the intrusive gas gradually diffused from one side of the annulus to the whole annulus. Second, the larger the fracture width, the larger the displacement window. Third, different from that in the vertical well section, the fracture width in the horizontal well section is the main factor affecting the displacement window, and the fracture height, drilling fluid density and viscosity have little influence on the displacement window, and the displacement interval is mainly in the negative pressure interval. Fourth, the displacement window of horizontal well displacement gas invasion is sensitive to the change of wellhead back pressure, and the slight increase or decrease of wellhead pressure will lead to the transition of gravity displacement to pure leakage or gas invasion. By simulating the dynamic process of horizontal well displacement gas invasion, this study explores the mechanism of horizontal well displacement gas invasion, which has certain guiding significance for the design of countermeasures for horizontal well displacement gas invasion.