New method for determining starting pressure gradient of tight gas reservoir

The invention discloses a new method for determining the starting pressure gradient of a tight gas reservoir, which comprises the following steps of: 1, loading a rock core into a rock core holder, heating to a preset formation temperature, applying confining pressure to a preset overlying rock pressure value, and simultaneously increasing internal pressure to preset pressure; 2, opening a back-pressure valve at the air outlet end of the rock core to keep the pressure constant, and maintaining the pressure at the air inlet end; 3, measuring end pressure values at two ends of the rock core and a gas flow value at a gas outlet end; gradually reducing the pressure of the gas outlet end, and metering the end pressure value and the gas flow value after each time of pressure reduction; 4, drawing a flow-pressure difference curve graph, determining a curve demarcation point, and determining a curve inflection point by using data before and after the curve demarcation point; and 5, obtaining a linear regression equat