Paper: Use of Short-Term, Multiple-Rate Flow Tests To Predict Performance of Wells Having Turbulence

A new analytical procedure is described here for predicting well performance and analyzing completion effectiveness of wells which have a significant pressure drop from turbulence. (In this discussion we use the term turbulence to describe both turbulence and all other rate dependent deviations from darcy flow such as inertial effects.) The procedure is more applicable to gas well completions but has been applied to a high-rate oil well. In particular, the new procedure should provide a powerful analytical tool in areas where most wells have high production potential. The procedure can be used in wells requiring sand control measures and in hydraulically fractured wells to determine if the cross-sectional area open to flow into the wellbore is sufficient. It also provides an indication of perforation effectiveness in normally completed wells because an abnormally high turbulence coefficient indicates too few open perforations. Incidental to determination of a turbulence coefficient, the new procedure provides a laminar flow coefficient which includes skin effect. If permeability thickness is known, an estimate of skin effect can be made from the laminar flow coefficient. Also included in the theory is an explanation of the effects of partial completion or a change in completion geometry on pressure buildup results when the turbulence pressure drop is significant. The analysis procedure permits determination of turbulence effects on completion efficiency irrespective of skin effect and laminar (darcy) flow. The required data are either: (1) two or more stabilized flow tests; or (2) two or more isochronal flow tests. Flow rates and bottomhole flowing pressures must be known in either case. Transient pressure data are not needed and bottomhole flowing pressures calculated from surface pressures may often be sufficient. The previous means of determining the turbulence coefficient have required some means of obtaining kh; usually a buildup test coupled with several production tests or a series of buildup tests. These were used to determine a total skin effect, s", which included the turbulence term. The s" values were then plotted versus flow rates. Actual skin effect and turbulence coefficients were then calculated from the intercept and slope. The new method avoids the necessity for transient data from a buildup or drawdown test and permits a direct plot of pressure data versus rate. The added simplicity should make the new procedure much more useful in direct field applications.