Patent Publication Number: US-6334489-B1

Title: Determining subsurface fluid properties using a downhole device

Description:
TECHNICAL FIELD 
     This invention relates generally to the field of downhole tools, and, more particularly, to downhole tools used for determining real time properties of fluids originating from subsurface earth formations. 
     BACKGROUND OF THE INVENTION 
     Electric downhole tools are used for determining various properties of fluids originating from subsurface earth formations. Conventional methods of using these devices involve using the tool to first withdraw a sample of fluid from a subsurface earth formation into a sample chamber of the tool. Thereafter, the volume of the sample chamber is incrementally increased, while the device measures the pressure, volume, and temperature of the sample. These measurements provide data for calculating fluid properties, such as bubble point pressure and compressibility. Unfortunately, these conventional tools are not operable during well production, and must be removed from a wellbore prior to flowing the well. 
     Accordingly, the present invention is directed to overcoming one or more of the limitations of the existing devices. 
     SUMMARY OF THE INVENTION 
     An apparatus for determining real time bubble point pressure of a fluid originating from a subsurface earth formation includes a sample chamber adapted to contain a sample of the fluid. A piston in the sample chamber adjusts the volume of the sample chamber. A pressure/temperature gauge fluidicly couples to the sample chamber, and monitors the pressure and temperature of the fluid sample within the sample chamber. A controller operably couples to the piston and pressure/temperature gauge. The controller continuously monitors the pressure, temperature, and volume of the sample fluid during expansion of the sample chamber. The controller also determines the bubble point pressure of the fluid, based on the pressure and volume measurements. 
     According to another aspect of the present invention, the controller of the same apparatus is also adapted to determine the compressibility of the sample fluid based on the pressure and volume measurements. 
     According to another aspect of the present invention, a method of determining real time bubble point pressure of a fluid originating from a subsurface earth formation includes first sampling the fluid during well production. After sample collection, the volume of the sample fluid is then incrementally increased, while the pressure, temperature, and volume of the sample fluid are monitored. The bubble point pressure of the sample fluid is then extrapolated from a graph of the pressure and volume measurements. 
     According to another aspect of the method of the present invention, after the step of monitoring, the compressibility of the sample fluid is then determined from a graph of the pressure and volume measurements. 
     According to another aspect of the present invention, a system for determining real time bubble point pressure of a fluid originating from a subsurface earth formation includes a production tubing adapted to facilitate the flow of fluid to the surface. A side pocket couples to the production tubing, and contains a downhole device. The downhole device is adapted to expand a sample of fluid. The downhole device is also adapted to measure the temperature and pressure of the sample of fluid. A remote controller, at the surface or downhole, operably couples to the downhole device. The controller is adapted to monitor the temperature, pressure, and volume of the sample of fluid. The controller is also adapted to determine the bubble point pressure of the fluid based on the pressure and volume measurements. 
     According to another aspect of the present invention, the controller of the same system is also adapted to determine the compressibility of the fluid, based on the pressure and volume measurements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a fragmentary cross-sectional view of a preferred embodiment of an apparatus for determining bubble point pressure and compressibility of a downhole fluid. 
     FIG. 2 depicts another fragmentary cross-sectional view of the preferred embodiment of FIG.  1 . 
     FIG. 3 depicts a fragmentary cross-sectional view of the preferred embodiment of FIG. 1 during sample collection. 
     FIG. 4 depicts a fragmentary cross-sectional view of the preferred embodiment of FIG. 1 during sample chamber expansion. 
     FIG. 5 depicts a fragmentary cross-sectional view of the preferred embodiment of FIG. 1 after further sample chamber expansion. 
     FIG. 6 depicts a flow chart of a preferred embodiment for determining bubble point pressure and compressibility of a fluid originating from a subsurface earth formation. 
     FIG. 7 depicts a plot of pressure as a function of volume. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The system, apparatus, and method of the present invention permit remote collection of a sample of wellbore fluid during well production. Following sample collection, the system, apparatus, and method permit remote expansion of the sample, as the temperature, pressure, and volume of the sample are monitored. The system, apparatus, and method then use the pressure and volume measurements to determine the real time bubble point pressure and compressibility of the sample of wellbore fluid. 
     Referring to FIG. 1, a system  100  for determining various properties of subsurface earth formation fluid includes a production tubing  105 , a side pocket  110 , a downhole device  115 , and a controller  120 . 
     The production tubing  105  includes a fluid passage  125 . The fluid passage  125  facilitates the flow of fluid originating from a subsurface earth formation to the surface. The production tubing diameter will vary depending upon the size and productivity of the well. 
     The side pocket  110  couples to and is supported by the production tubing  105 . The side pocket  110  houses the downhole device  115 . 
     The downhole device  115  couples to and is supported by the production tubing  105 . The downhole device  115  includes a wireline  130 , a motor  135 , a spindle  140 , a piston  145 , a sample chamber  150 , a first flow line  155 , a first solenoid valve  160 , a second flow line  165 , a third flow line  170 , a fourth flow line  175 , a second solenoid valve  180 , a pressure/temperature gauge  185 , an inlet port  190 , and a pressure equalization port  195 . 
     The wireline  130  operably couples to the controller  120 , the motor  135 , the first solenoid valve  160 , the second solenoid valve  180 , and the pressure/temperature gauge  185 . 
     The motor  135  connects to the spindle  140 . The motor  135  moves the spindle  140 . The motor  135  comprises a  30  DC volt motor that has an outer diameter dimension of about 1.0 inch and a length of about 3.0 inches. 
     The spindle  140  connects to the piston  145 . The piston  145  adjusts the volume of the sample chamber  150 . The piston  145  is stainless steel, and has outer diameter dimension of about 0.75 inches. A plurality of annular piston rings  197  couple to the piston  145 . The annular piston rings  197  form a seal between the inner diameter of the sample chamber  150  and the piston  145 . 
     The sample chamber  150  couples to the lower edge of the motor  135 . The sample chamber  150  houses the spindle  140  and piston  145 . The sample chamber is adapted to contain a sample of fluid. The sample chamber  150  is stainless steel, and has an outer diameter dimension of about 1.0 inch, an inner diameter dimension of about 0.75 inches, and a length of about 3.0 inches. 
     The pressure equalization port  195  is located in the upper region of the sample chamber  150 . The pressure equalization port  195  is a channel that connects the sample chamber  150  to the fluid passage  125  of the production tubing  105 . The pressure equalization port  195  functions to minimize the pressure difference across the piston  145 . The pressure equalization port  195  has an inner diameter of about 0.25 inches. 
     The first flow line  155  connects at an upper end to a lower portion of the sample chamber  150  and at a lower end to the fourth flow line  175 . The first flow line  155  extends substantially vertically downward from the sample chamber  150 . The first flow line  155  fluidicly connects the sample chamber  150  to the fourth flow line  175  and the second flow line  165 . The first flow line  155  is adapted to contain a sample of fluid. The first flow line  155  is stainless steel tubing with an outer diameter dimension of about 0.25 inches and an inner diameter dimension of about 0.1875 inches. 
     The first solenoid valve  160  couples to the first flow line  155 . The first solenoid valve  160  opens and closes the first flow line  155 . The first solenoid valve  160  is a stainless steel valve. 
     The second flow line  165  connects at one end to the first flow line  155  and at the other end to the third flow line  170 . The second flow line  165  extends in a substantially horizontal direction. The second flow line  165  fluidicly connects the first flow line  155  to the third flow line  170 . The second flow line  165  is adapted to contain a sample of fluid. The second flow line  165  is stainless steel tubing with an outer diameter dimension of about 0.25 inches and an inner diameter dimension of about 0.1875 inches. 
     The third flow line  170  connects at an upper end to the second flow line  165  and at a lower end to the pressure/temperature gauge  185  and the fourth flow line  175 . The third flow line  170  extends substantially vertically downward from the second flow line  165 . The third flow line  170  fluidicly connects the second flow line  165  to the pressure/temperature gauge  185 . The third flow line  170  is stainless steel tubing with an outer diameter dimension of about 0.25 inches and an inner diameter dimension of about 0.1875 inches. 
     The pressure/temperature gauge  185  fluidicly connects to the third flow line  170 . The pressure/temperature gauge  185  monitors the pressure and temperature of the fluid sample within the sample chamber  150 . The pressure/temperature gauge  185  is a product designated by model number TMC20K, manufactured by Quartzdyne, Inc. in Salt Lake City, Utah. 
     The fourth flow line  175  fluidicly connects at one end to the third flow line  170  and on the other end to the inlet port  190 . The fourth flow line  175  also connects to the first flow line  155 . The fourth flow line  175  extends in a substantially horizontal direction. The fourth flow line  175  connects the third flow line  170  and the first flow line  155  to the inlet port  190 . The fourth flow line  170  is stainless steel tubing with an outer diameter dimension of about 0.25 inches and an inner diameter dimension of about 0.1875 inches. 
     The second solenoid valve  180  is connects to the fourth flow line  175 . The second solenoid valve  180  opens and closes the fourth flow line  175 . The second solenoid valve  180  is a stainless steel valve. 
     The inlet port  190  connects to the fourth flow line  175 . The inlet port  190  is an opening that connects the fourth flow line  175  to the fluid passage  125  of the production tubing  105 . The inlet port  190  facilitates the withdrawal of fluid from the fluid passage  125  into the sample chamber  150  and the flow lines  155 ,  165 ,  170 , and  175 . The inlet port  190  has an inner diameter of about 0.25 inches. 
     The controller  120  operably couples to the downhole device  115  through the wireline  130 . The controller  120  remotely operates the downhole device  115 . The controller  120  continuously monitors the pressure, temperature, and volume of the sample fluid during expansion of the sample chamber  150 . The controller  120  determines the bubble point pressure and compressibility of the sample fluid based on the pressure and volume measurements. The controller  120  can be any conventional, commercially available programable controller or a computer. 
     Referring to FIG. 2, in operation, an operator first positions the system  100  within a wellbore  200 . The wellbore  200  includes a hole  205  extending into a subsurface earth formation  210  containing a formation fluid  215 . The wellbore  200  is lined with cement  225  and a casing  230 . Perforations  235  adjacent to the formation  210  allow formation fluid  215  to flow into the fluid passage  125  of the production tubing  105 . 
     Referring to FIG. 3, to collect a sample of fluid, the controller  120  remotely opens the first solenoid valve  160 , closes the second solenoid valve  180 , and vertically moves the piston  145 . The controller  120  continues to vertically move the piston  145  upward until a predetermined volume of fluid has been withdrawn from the fluid passage  125  into the sample chamber  150 . 
     Referring to FIG. 4, after sample collection, the controller  120  remotely closes the first solenoid valve  160  to confine the sample fluid within the sample chamber  150  and the flow lines  155 ,  165 ,  170 , and  175  bounded by the closed solenoid valves  160  and  180 . The controller  120  then incrementally moves the piston  145  upward, thereby increasing the volume of the sample chamber  150 . As the controller  120  incrementally moves the piston  145 , the pressure/temperature gauge  185  continuously measures the pressure and temperature of the sample contained within the sample chamber  150 . 
     Referring to FIG. 5, when the sample chamber  150  volume is increased, such that the pressure of the sample of fluid is less than the bubble point pressure of the fluid, gas  500  in the sample of fluid releases from solution, thereby forming a two phase mixture of liquid and gas  500 . 
     During sample chamber  150  expansion, the controller  120  remotely monitors the temperature and pressure measurements made by the pressure/temperature gauge  185 . The controller  120  also calculates the volume of the sample fluid based on the position of the piston  145  within the sample chamber  150 . After sufficient pressure and volume data has been collected, the controller  120  determines the real time bubble point pressure and compressibility of the sample fluid. 
     Referring to FIG. 6, a method for determining the real time bubble point pressure and compressibility of a fluid originating from a subsurface earth formation begins with a step  600 . In step  600 , an operator positions the system  100  in the wellbore  200 . In step  605 , the controller  120  remotely opens the first solenoid valve  160 , closes the second solenoid valve  180 , and vertically moves the piston  145  upward to withdraw a sample of fluid from the fluid passage  125  into the sample chamber  150 . In step  610 , the sample is confined to the sample chamber, and expanded as the controller vertically moves the piston  145  upward. In step  615 , the controller  120  monitors the pressure, temperature, and volume of the sample. In step  620 , the controller  120  determines whether further sample expansion is necessary. Further sample expansion will be necessary if additional data points are needed to make the requisite calculations. If further expansion is necessary, the method repeats steps  610  and  615 . If further expansion is not necessary, then in step  625 , the controller  120  determines the bubble point pressure and compressibility of the sample. 
     Referring to FIG. 7, a graphic representation of pressure and volume data collected by the system  100  includes a plot of sample fluid pressure as a function of volume data  700 . The data  700  exhibits two different linear slopes. A first best-fit line  705 , drawn through the data  700 , exhibits a first slope. A second best-fit line  710 , drawn through the data  700 , exhibits a second, smaller slope. The first best-fit line  705  corresponds to pressures at which the sample fluid is a single phase liquid. The second best-fit line  710  corresponds to pressures at which the sample fluid is a two phase gas-liquid mixture. The bubble point pressure  715  of the sample fluid corresponds to the pressure at which the first best-fit line and the second best-fit line intersect. The compressibility of the sample of wellbore fluid, at a particular pressure and volume, is calculated using the following formula:        compressibility   =       -     1     V   2         ×       (       V   2     -     V   1       )       (       P   1     -     P   2       )                         
     where, 
     V 1 =volume at higher pressure 
     V 2 =volume at lower pressure 
     P 1 =higher pressure 
     P 2 =lower pressure. 
     It is understood that several variations may be made in the foregoing without departing from the scope of the invention. For example, the downhole device  115  may be operated without a wireline  130 . In such a configuration, the downhole device  115  may be operated using a memory tool that is attached to the downhole device  115  in the wellbore  200 , and retrieved at a later time. Alternatively, the downhole device  115  may be remotely operated with a transmitter. 
     Although illustrative embodiments of the invention have been shown and described, a wide range of modifications, changes, and substitutions is contemplated in the foregoing disclosure. In some instance, some features of the present invention may be employed without a corresponding use of the other features. Accordingly, it is appropriate that the appended claims be construed broadly, and in a manner consistent with the scope of the invention.