Patent ID: 8261819
Filing Date: 2012-09-11
Classification: E21B

Abstract:
1. A method of determining a fluid level in a space in a well utilizing a conduit in gaseous communication with the space in the well, a valve controlling gaseous communication through the conduit, and a downstream surge space for inrush, the conduit, the valve, and the surge space forming a closed system substantially sealed from the atmosphere, comprising: determining ambient pressure in the conduit with the valve open and gas being produced in the space by the well; closing the valve to cause gas pressure within the conduit to increase a selected amount above the ambient pressure; opening the valve for a selected time interval and then re-closing the valve to cause the conduit and the surge space to be in gaseous communication for the selected time interval to create a rarefaction wave in the conduit and in the well without substantially venting gas into the atmosphere, wherein the rarefaction wave is created within the closed system by energy from the well itself without application of mechanical force by an external apparatus; taking a plurality of conduit pressure measurements for a selected time, the time selected to allow the rarefaction wave to travel at a previously determined speed to a fluid top within the space in the well and then return to the surface; evaluating the plurality of pressure measurements to determine a round-trip time for the rarefaction wave to travel to the fluid top and return to the surface, the round-trip time being the time difference between initiation of the wave and its return to the surface; and determining fluid level as half the product of wave speed and round-trip time.