Predicting Performance of Waterfloods at Highest Constant Injection Rate
Authors: Higgins R.V. 
Published: December 2007

Using the principles of dimensionless ratios, the data from a Higgins-Leighton method at constant pressure may be easily and quickly usedto predict the pressure may be easily and quickly usedto predict the highest constant rate of injection of water that is possible without fracturing the reservoir rock at the possible without fracturing the reservoir rock at the wellbore,to predict quickly the performance to the ultimate life of a waterflood with a constant rate of injection,to predict the life of a waterflood using a high constant rate early in the flood when the pressure at the wellhead may be low and then, later, a pressure at the wellhead may be low and then, later, a reduced rate to avoid fracture, andto estimate, after the flooding is started, the time at which the kick (first increase in oil rate) will occur and the relative size of the kick.

These are all useful in making an economic analysis of a potential waterflood. With the method presented we can quickly process the predictions using relative permeabilities that appreciably influence recovery of oil. The method includes the use of layers to determine the effect of vertical permeability variations. All of this information is useful in designing the constant-rate pumps used to inject water into reservoirs. With these features, we can use the predicted performance at a constant pressure to obtain the predicted performance history at a constant injection rate during the entire life of the flood. Also, we can quickly predict the performance of a flood at different constant rates performance of a flood at different constant rates during the life of the flood; that is, at a very high rate for the short initial period when the well may be operating under nearly vacuum conditions at the wellhead, then at decreasing sets of constant rates or even at continuously changing rates. The economics of a flood is affected by the size and cost of constant-rate pumps and the rate of return of the investment during the life of a flood. With the performance data vs the rate of injection, the performance data vs the rate of injection, the economic feasibility can be easily determined. The relationships among time, rates and volumes have been checked by computer runs. They were tested on the individual layers and on combinations of layers of different absolute permeability. The ratio relationship was found to reproduce exactly the produced volumes and other data. At the time of this produced volumes and other data. At the time of this writing, it has not been tested on combinations of layers of different relative permeability-saturation curves. But, in principle, it should hold for these combinations also. The highest constant injection rate that will require a pressure just less than would be expected to fracture the formation can be determined with a model computer run at constant pressure. When the mobility ratio is greater than one, the injection rate for the model will decrease, pass through a minimum, and then increase. This minimum injection rate is the maximum permissible constant injection rate. Any constant rate in excess of this would require a pressure that would probably fracture the formation at pressure that would probably fracture the formation at some time during the flood. This highest permissible pressure is used in the Higgins-Leighton prediction method. The printout of the results of the calculations using the Higgins-Leighton method at constant pressure or a plot of the results will show lowest injection rate.

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