Wells – Processes – Producing the well
Reexamination Certificate
1999-11-22
2001-07-17
Tsay, Frank S. (Department: 3672)
Wells
Processes
Producing the well
C166S068000
Reexamination Certificate
active
06260627
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a system and method for improving the fluid dynamics, specifically viscosity and gas-to-liquid ratio, of well fluids produced from reservoirs by a pumping system.
BACKGROUND OF THE INVENTION
Pumping systems, such as electric submersible pumping systems, are commonly used to transport fluids from a first location to a second remote location. An example of such a system is that used for transporting subterranean reservoir fluids from one location to another. A conventional application involves the pumping of fluids from a wellbore to a collection location at the surface of the earth.
Difficulties in transport can arise when the fluid to be transported is too viscous for adequate flow, and/or the fluid has an excessive gas-to-liquid ratio. Both of these types of problems can result in inadequate flow of the fluids through the pumping system and eventual system failure. The present invention solves such problems associated with pumping certain subterranean fluids.
Attempts have been made to lower the viscosity of high viscosity fluids by deploying heaters, in the form of heat trace tape and coil elements, in the wellbore. Such prior heater solutions, however, can have limited applications, require expensive secondary power cabling, and are prone to damage due to thermal cycling and corrosive environments. Oversized pumps and motors also have been used to pump such fluids. This solution, however, is less cost efficient, as the larger pumps and motors are substantially more expensive, require higher cost power cable and incur greater electric utility costs.
Other attempts have been made to inject well fluid with lower viscosity fluids or steam from a secondary and independent supply. The injection approach, while functional, requires an expensive supply source and tubing for directing the injected fluids. Such injection systems require regular maintenance and make the installation and support complex and expensive. Also, steam injection causes an increase in the gas-to-liquid ratio, thereby reducing the overall pumping system efficiency and potentially causing gas lock in the pump.
With respect to high gas-to-liquid ratio well fluids, problems include failure of the pumping system or at least a significant decrease in the overall efficiency of the pumping system. Prior solutions have included installation of commercially available rotary gas separators. While such gas separators are generally effective, they add cost to the system and have limited efficiency.
Other attempts have been made to locate the pumping equipment below the wellbore fluid inlet for the reservoir, e.g. wellbore casing perforations. While locating the equipment below the reservoir inlet has been effective for allowing a portion of the free gas to naturally vent to a location above the reservoir, a problem with this approach is that it can result in an inadequate flow rate past the motor, thereby causing excessive motor heating and resultant failures. Although excessive motor heating has been addressed in these applications through secondary solutions, such as flow diverting shrouds and recirculation systems, such secondary solutions are designed to cool the motor and are not intended to lower the gas-to-liquid ratio.
There is an increased need to provide enhanced and hybrid solutions to the problems of high viscosity and high gas-to-liquid ratios in wellbore fluids to facilitate production from otherwise marginal reservoirs.
SUMMARY OF THE INVENTION
The present invention features a system for pumping a wellbore fluid that has accumulated in a wellbore. The wellbore is of the type lined by a wellbore casing having at least one perforation to permit entry of the wellbore fluid. In particular, the system is amenable for pumping wellbore fluids having a high gas-to-liquid ratio.
The overall design includes a submersible pumping system having a submersible motor, a motor protector, a submersible pump driven by the submersible motor and a pump intake. The pumping system is located in the wellbore by a deployment system, e.g. production or coiled tubing, having a length that maintains the submersible pumping system above the at least one perforation. Furthermore, a bypass is connected into the system in a manner such that a portion of the wellbore fluid intaken by the submersible pumping system is directed to a position below the pump intake. This bypassing of a portion of the fluid both reduces the concentration of gas in the fluid intaken and lowers its viscosity.
According to another aspect of the invention, a system is provided for pumping a well fluid from a location in a wellbore. The system includes a submersible pumping system having a submersible motor, a submersible pump powered by the submersible motor and a pump intake having a fluid intake opening. The system further includes a bypass located to collect a portion of fluid from a location downstream of the fluid intake opening. The bypass is configured to direct the portion of fluid to a wellbore location upstream of the fluid intake opening. Additionally, the system includes a flow controller disposed to selectively control the amount of fluid flow through the bypass.
According to another aspect of the present invention, a method is provided for recovering a high gas-to-liquid fluid from a well. The method includes positioning a submersible pumping system in a well fluid, and pumping the well fluid to a desired location. The method further includes recirculating a portion of well fluid intaken by the submersible pumping system to a location upstream of the intake for the submersible pumping system. Also, the method includes selectively controlling the amount of well fluid that is recirculated.
According to yet another aspect of the present invention, a method is provided for recovering a high gas-to-liquid fluid from a wellbore. The wellbore is of the type lined by a wellbore casing having a perforation to permit entry of a reservoir fluid into the wellbore. The method includes positioning a submersible pumping system in the wellbore at a position above the perforation. Additionally, the method includes directing a wellbore fluid portion, intaken by the submersible pumping system, through a bypass. The wellbore fluid portion is discharged back into the wellbore at a position for intake by the submersible pumping system.
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Camco International Inc.
Fletcher Yoder & Van Someren
Tsay Frank S.
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