Initially Gas Wells usually flow at sufficiently high rates to remove all liquids from the wellbore. When the gas flow rate decreases below critical rate1 some intervention such as compression, surfactants, and/or velocity strings is required. At a later time when either reservoir pressure and/or gas flow rate is sufficiently reduced, then other means of artificial lift (usually such as plunger lift, gas lift, or sucker rod lift) must be added to maintain production. Acoustic fluid level testing can be used to investigate the producing condition of a gas wells. Developments in digital acoustic fluid level technology have resulted in the operator being able to undertake fluid level measurements and use this technology to investigate the status of his gas wells. The act of acquiring a fluid level on a gas well is an inexpensive and non-intrusive process. Examples of acoustic tests are presented, where the test are performed on shut-in or flowing above or below critical flow rate gas wells with or without surfactant treatments acquired down the tubing or the tubing/casing annulus.
Techniques for acoustic liquid level analysis are discussed for gas wells where unusual conditions exist such as very shallow liquid levels, very deep liquid levels, noisy wells, high bottomhole temperature, and low or high surface pressures. Some gas wells have gas lift mandrels, liners, multiple zones of perforations, tubing holes, flush pipe and other conditions which result in the acquisition of difficult to interpret acoustic traces. This paper describes analysis techniques used to determine the distance to the liquid level in gas wells with these unusual conditions. The analysis is based on data obtained at the surface without entering the wellbore and yields accurate representation of the conditions existing on the surface, within the wellbore and within the reservoir.