METHOD TO DETECT FLUID LEVEL IN OIL WELL Russian patent published in 2012 - IPC E21B47/47 G01F23/296 

FIELD: oil and gas industry.

SUBSTANCE: pulse acoustic signal is generated at a wellhead in a tubular space. The acoustic echo signal reflected from the liquid is received. It is converted into an electric signal. Time of acoustic signal travelling from the wellhead to the fluid level is determined, as well as positions of sections with higher and lower acoustic density of gas, variation of sound speed distribution and position of non-standard space irregularities. The fluid level is determined depending on values of sound speed at well sections, as well as time of passage of an acoustic signal from the wellhead to the fluid level. At the same time the electric signal is exposed to analog-to-digital conversion, and the digitised signal is exposed to Fourier transform at each current section of the echogram in compliance with the mathematical formula. Spectrogram graphic image is built in the form of a 3D surface, where location of standard and non-standard irregularities is identified in the tubular space. Values of height are identified, at which the spectrum module has the maximum value at the specified time position of the echogram section. Dependence of sound speed on time is determined with account of the distance between neighbouring standard irregularities at the specified time position of the echogram section using the formula. And fluid level in the well is identified by discrete integration of sound speed function in the gap from the wellhead to the fluid level.

EFFECT: higher accuracy of fluid level detection in the well.

4 cl, 10 dwg