Patent ID: 6237410
Filing Date: 2001-05-29
Classification: E21B,G01F

Abstract:
A method of determining the depth to fluid in a well where a downhole pump is attached to a string of production tubing that is connected together with collars and the production tubing is disposed inside a well casing so as to form an annulus between the casing and the production tubing and the annulus is partially filled with fluid to be pumped and the annulus above a fluid surface is filled with gasses, the method comprising:generating and transmitting an acoustic pulse into the annulus inside the well casing;detecting reflections of the acoustic pulse from collars on the production tubing and from the fluid surface to obtain a digital reflection signal;analyzing the digital reflection signal using amplitude demodulation to determine the location of the start of the acoustic pulse within the reflection signal;analyzing the digital reflection signal using amplitude demodulation to determine the location of the reflection from the fluid surface within the reflection signal;analyzing the digital reflection signal using amplitude demodulation to detect reflections from collars within the reflection signal; andapplying a known distance to each collar reflection detected between the start of the acoustic pulse and the refection from the fluid surface to provide the distance from the top of the well to the fluid surface.