Method for operating a process for the extraction of a fluid in a borehole, in which the location of an interface depth is detected in the borehole during deep drilling, a pressure measurement of the pressure at the head of the borehole is made, the pressure at the bottom of the borehole is determined from the measured pressure at the head of the borehole and the determined location of the interface depth, the determination of this pressure is utilized for regulating the performance of an extracting device for the fluid to be extracted; to detect the location of the interface depth in the borehole in deep boreholes at the earth's surface an acoustic event takes place in a targeted manner which generates acoustic pressure waves, the pressure waves generated by the event run into the depth in the borehole, the pressure waves travelling in the borehole are reflected at least also at the interface depth, at the earth's surface pressure waves travelling from the borehole are captured and the travel time since the acoustic event is measured, the captured and measured pressure waves are evaluated and together with the associated travel time the location of the interface depth is deduced, the acoustic event generates signal patterns with a given, time-varying frequency spectrum, the signal pattern is radiated into the borehole as an oscillation event, runs into the depth and is reflected, at the earth's surface collected signals from the borehole are analyzed, from the collected signals during the analysis, oscillation events are filtered out which correlate to the radiated signal pattern, the location of the interface depth is deduced from the oscillation events correlating to the radiated signal pattern among the collected signals and the travel time since the radiation of the signal pattern, characterized, in that the performance of the extracting device is regulated in such a way that constant inflow rates and/or a constant location of the interface depth prevail and further characterized, in that the pressure at the bottom of the borehole is always kept above the boiling point pressure or gas release point or the start of degassing. the determination of this pressure is utilized for regulating the performance of an extracting device for the fluid to be extracted; to detect the location of the interface depth in the borehole in deep boreholes at the earth's surface an acoustic event takes place in a targeted manner which generates acoustic pressure waves, the pressure waves generated by the event run into the depth in the borehole, the pressure waves travelling in the borehole are reflected at least also at the interface depth, at the earth's surface pressure waves travelling from the borehole are captured and the travel time since the acoustic event is measured, the captured and measured pressure waves are evaluated and together with the associated travel time the location of the interface depth is deduced, the acoustic event generates signal patterns with a given, time-varying frequency spectrum, the signal pattern is radiated into the borehole as an oscillation event, runs into the depth and is reflected, at the earth's surface collected signals from the borehole are analyzed, from the collected signals during the analysis, oscillation events are filtered out which correlate to the radiated signal pattern, the location of the interface depth is deduced from the oscillation events correlating to the radiated signal pattern among the collected signals and the travel time since the radiation of the signal pattern, characterized, in that the performance of the extracting device is regulated in such a way that constant inflow rates and/or a constant location of the interface depth prevail and further characterized, in that the pressure at the bottom of the borehole is always kept above the boiling point pressure or gas release point or the start of degassing.