K.B. Nolen, & S.G. Gibbs, Nabla Corp.
A new computerized fluid level measurement method is described. Instead of using the traditional gas gun and microphone system, a transient wave is created by venting a small amount of gas from the casing and the fluid level is located with help of an ordinary pressure transducer. The method measures acoustic velocity of well gas external to the well in a known length of coiled tubing. This eliminates the need to count tubing collars to determine velocity. Much of the equipment is off-the-shelf, and cost is less than with traditional systems. Results from field measurements show that the new method provides accuracy which is comparable to traditional systems. The new technique presents an uncluttered result without electrical or digital filtering which clearly shows the fluid level in the majority of cases. The simplicity of the return echo helps differentiate other objects and conditions that might pose as fluid level such as uphole leaks, liner tops, and tubing anchors. The paper discusses many practical applications of the technique in locating fluid levels. It also describes how CO2 movement within the reservoir can be tracked as a by-product of measuring fluid levels. The paper also illustrates how the wave equation can be used to explain various fluid level echoes encountered in the field.