Abstract

The paper describes the results of a simulation study of a novel method to control water coning in an oil producing well. This method uses a dual completion configuration: above and below OWC. In this configuration, the well section above OWC is completed In the oil zone and produces oil, while the well section completed below OWC In the water-saturated zone serves as a drain to control the rise of the water cone (tailpipe water sink).

The physical principle of coning control In this method results from the effect of the water sink upon flow potential between the sink and oil-production perforations. The effect depends upon the water sink flowrate, and It results In suppression of water coning.

The objective of this study was to investigate production performance of the well with and without the water sink performance of the well with and without the water sink tailpipe. At first, the water sink's position and flowrate were investigated as they affected the critical production rate of oil, i.e. maximum production rate without the water breakthrough. Next, a comparison was made between the amounts of water produced for greater than critical oil production rates in these produced for greater than critical oil production rates in these two systems.

The comparison tests were designed as a series of simulated oil production cycles in a well/reservoir system of known geometry and reservoir properties. The coning behavior of the production system with the tailpipe water sink was production system with the tailpipe water sink was mathematically modelled using the flow potential distribution generated by two constant-terminal-rate sinks located between the two linear boundaries and the constant-pressure outer radial boundary. This new model was verified by using the existing and simulated data of water coning in conventional wells and by setting the water sink flowrate at zero, with oil being the only produced fluid. Verification tests were used to select the type of oil reservoir with the thick oil zone and the small dip angle for further comparison studies.

In these studies, the amount of produced water with and without the tail water sink was calculated for production rates exceeding the water breakthrough levels In conventional wells. Field data was compared to the results obtained from the water sink model.

The study demonstrated the existence of an active mechanism to control water coning with the tailpipe water sink. The mechanism is particularly effective with low flowrate at the sink because it prevents the water cone from breaking through the oil zone into the producing perforations. Also evaluated were the configurations of the well/reservoir system for the tailpipe water sink process. This process yielded less produced water than the conventional method did at the same or higher oil rate.

Introduction

Though the mechanism of water coning is well known, its control is very limited. The reason is that only three out of seven coning variables can be controlled. To substantiate this statement, let us overview the known facts about water coning and its control.

Parameters affecting water coning in vertical wells are: the mobility ratio, oil zone thickness, ratio of gravity forces to viscous forces, well spacing, ratio of horizontal permeability to vertical permeability, and well penetration permeability to vertical permeability, and well penetration and production rate. The first three variables are practically beyond technical control.

The mobility ratio effect on water coning was studied using scaled laboratory models]. Studies with a radial model[11 showed that mobility ratio inversely affects production performance. Also, the ratio of water mobilities, in the performance. Also, the ratio of water mobilities, in the aquifer and water-invaded zones, positively affects production performance. Studies with another three-dimensional performance. Studies with another three-dimensional model revealed that mobility ratio values greater than one engendered the worst coning effects. The higher the mobility ratio was, the faster the breakthrough occurred. The study showed that when the mobility ratio is greater than one, the water coning rises quickly and the water cut goes through a rapid increase. As production continued, the cone expanded in all directions and lowered oil production to within a few percent of its initial value. percent of its initial value. P. 237

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