Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Molecular weight
Reexamination Certificate
1999-02-01
2001-06-26
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Molecular weight
C166S264000, C073S152020
Reexamination Certificate
active
06250138
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to the field of wireline tools used for subsurface earth formation testing, and more particularly to wireline tools used for determining the bubble point pressure of fluid flowing from a subsurface formation.
Electric wireline tools are used for determining bubble point pressure of fluid originating from a subsurface earth formation in order to determine properties of the fluid used in calculating the total fluid content within the formation. One of the methods of determining in situ bubble point pressure of formation fluid involve the use of downhole electric wireline tools capable of withdrawing a sample of fluid from a subsurface earth formation into a sample chamber and incrementally expanding the volume of the sample chamber while measuring the pressure. The bubble point pressure of the fluid is then extracted from a plot of the pressure versus volume data. These conventional tools are used only in the exploration stage, are not useable during well production, and are removed from the wellbore prior to flowing the well.
Other conventional methods of determining bubble point pressure of a formation fluid involve withdrawing a sample of fluid from the earth formation into a chamber of a testing tool. Then, the bubble point pressure measurement is done at the well site or laboratory by measuring the pressure and volume of the sample, while expanding the volume of the sample. Such conventional tools are not permanently installed, and do not permit the determination of in situ fluid bubble point pressure during well production.
Conventional methods and apparatus for remotely controlling well production employ the use of various downhole electromechanical devices coupled with computer based surface systems. One such device is an adjustable choke with pressure sensors located upstream and downstream of the choke for attaining desired wellbore pressure by controlling fluid flow during the life of the well. However, such devices do not use the adjustable choke in determining a bubble point pressure of the fluid.
Therefore, a need exists for a method for determining fluid bubble point pressure during well production.
The present invention is directed to overcoming one or more of the limitations of the existing devices.
Summary of the Invention
According to one aspect of the present invention, an apparatus for determining a bubble point pressure of a fluid originating from a subsurface earth formation is provided that includes production tubing, an adjustable choke, and a controller. The production tubing is adapted for placement within the subsurface earth formation. The adjustable choke is coupled to the production tubing. The adjustable choke includes a remotely adjustable choke opening adapted to selectively restrict a flow rate of a fluid flowing through the choke opening, and a pressure sensor adapted to measure a fluid pressure downstream of the choke opening. The controller is operably coupled to the adjustable choke and is adapted to control the adjustable choke opening, monitor the fluid pressure downstream of the choke opening, and calculate the bubble point pressure.
According to another aspect of the present invention, a method of determining a bubble point pressure of a fluid originating from a subsurface earth formation is provided that includes placing an adjustable choke in communication with the fluid flowing from the subsurface formation. The size of the adjustable choke is selectively adjusted to vary the flow rate downstream from the adjustable choke. The fluid pressure downstream from the adjustable choke is measured for a range of choke sizes. The plot of the fluid pressure downstream against choke size will indicate fluid phase change from one phase (liquid), as shown by a first line, into two phases (liquid and gas), as shown by a second line. The intersection of these two best fit lines indicates the bubble point pressure for the fluid.
According to another aspect of the present invention, a method of determining a bubble point pressure of a fluid originating from a subsurface earth formation using an adjustable choke positioned downhole adjacent to the formation is provided that includes placing the adjustable choke in communication with the fluid flowing from the formation to the surface during well production. The adjustable choke has a selectively operable actuator for remotely adjusting the size of an opening of the choke in order to vary the downstream flowrate of the fluid flowing through the opening. The choke also includes a pressure sensor located adjacent to the choke opening for measuring the downstream pressure of the fluid after flowing through the choke opening. The pressure sensor communicates the pressure measurements to a controller. The size of the adjustable choke is selectively adjusted to varying the downstream fluid flowrate while simultaneously measuring the downstream fluid pressure. Downstream fluid pressure data at several choke sizes is obtained to generate a first plot of downstream pressure vs choke size data which contains data exhibiting substantially linear behavior having a first slope and a second plot of downstream pressure vs choke size data which contains data exhibiting substantially linear behavior having a second slope. The plotted data are then extrapolated to determine the intersection of the first and second plots to determine the bubble point pressure of the fluid.
REFERENCES:
patent: 4782695 (1988-11-01), Glotin et al.
patent: 4860581 (1989-08-01), Zimmerman et al.
patent: 5579842 (1996-12-01), Riley
patent: 5635631 (1997-06-01), Yesudas et al.
patent: 5706892 (1998-01-01), Aeschbacher, Jr. et al.
patent: 6058773 (2000-05-01), Zimmerman et al.
Flecker Mike
Shwe Than
Thompson Steve
Torrance Roy
Haynes & Boone L.L.P.
Mattingly Todd
Politzer Jay L.
Williams Hezron
Wood Group Logging Services Holdings, Inc.
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