A single phase sampling apparatus and method for retrieving a formation fluid sample at or above the bubble point of the sample. The apparatus utilizes a gas charge contained between a sample piston and a charging piston to maintain a formation sample at the desired pressure. The charging piston utilizes the hydrostatic pressure present at the depth of the desired formation sample to compress and therefore increase the gas charge to the appropriate pressure necessary to maintain the formation sample at the desired pressure. The utilization of hydrostatic pressure to increase the pressure of the gas charge allows the use of a low pressure gas charging system to prepare the apparatus prior to sampling, thereby increasing the safety and ease of use of the device.
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21. A method for downhole fluid sample collection comprising the steps of:
providing a tube with a first end and a second end, and a first piston and a second piston located within said tube;
inserting pressurized gas in the space between said first and second piston;
lowering the tube downhole;
collecting a formation fluid sample in the space between the first end of the tube and said first piston;
raising said tube with said formation fluid sample.
1. A formation fluid sample bottle comprising:
a cylindrical tube with an enclosed top end and an open bottom end;
a sample piston slidingly inserted into said cylindrical tube to form a sample chamber inside said cylindrical tube between said enclosed top end and said sample piston;
a charging piston slidingly inserted into said cylindrical tube between said sample piston and said open bottom end to form a pressurized gas chamber inside said cylindrical tube between said sample piston and said charging piston; and
an end cap fixed to said open bottom end;
wherein:
said charging piston includes a valve to allow the introduction of a pressurizing gas into said pressurized gas chamber.
20. A pressurizing piston for use in collecting formation fluid samples downhole and maintaining the pressure of the sample above the bubble point of the sample, comprising:
a cylindrical main body with a distal end, a proximal end and a threaded axial bore;
a check valve inserted into said axial bore at said distal end of said main body;
a plunger with a narrowed diameter distal section, an open proximal end, an axial bore, an outer circumference with at least one O-ring located at said outer circumference, and threads located on said outer circumference engaged to said cylindrical main body threaded axial bore; and
a release plug inserted into said plunger open proximal end to seal off said plunger axial bore.
10. A single phase formation evaluation tool comprising:
at least one formation fluid sample bottle with an enclosed top end, an open bottom end and an axial bore extending through said formation fluid sample bottle;
a sample piston slidingly inserted into said axial bore of said formation fluid sample bottle to form a collection chamber within said axial bore, between said enclosed top end and said sample piston;
a charging piston slidingly inserted into said axial bore of said formation fluid sample bottle below said sample piston, to form a pressurized gas chamber within said axial bore, between said sample piston and said charging piston; and
an end cap fixed to said open bottom end of said formation fluid sample bottle.
22. A method for extracting a single phase fluid sample from a wellbore formation and maintaining the sample in a single phase, comprising the steps of:
forcing a sample piston and a charging piston together within a formation fluid sample bottle to purge any existing gas from a pressurized gas chamber;
attaching a pressurized gas source to said charging piston;
forcing pressurized gas through said charging piston into said pressurized gas chamber;
removing said pressurized gas source from said charging piston. inserting said formation fluid sample bottle into a formation evaluation tool;
lowering said formation evaluation tool into a wellbore to a desired formation depth;
allowing hydrostatic pressure from said wellbore to force said charging piston toward said sample piston to further pressurize said pressurized gas;
pumping formation fluid into said single phase collection apparatus;
raising said formation evaluation tool; and
removing said single phase collection apparatus from said formation evaluation tool.
2. The formation fluid sample bottle of
4. The formation fluid sample bottle of
at least one O-ring located at said outer circumference;
an axial bore extending through said charging piston; and
a check valve positioned in said axial bore.
5. The formation fluid sample bottle of
6. The formation fluid sample bottle of
a distal end and a proximal end;
an axial bore;
a narrowed diameter section at said distal end; and
a release plug inserted into said axial bore at said proximal end.
7. The formation fluid sample bottle of
said plunger additionally has an outer circumference and further comprises:
at least one O-ring located at said outer circumference; and
said outer circumference of said plunger is provided with threads for attachment to said axial bore of said charging piston.
8. The formation fluid sample bottle of
9. The formation fluid sample bottle of
11. The single phase formation evaluation tool of
at least one O-ring located at said circumference;
an axial bore extending through said charging piston; and
a check valve positioned in said axial bore.
12. The single phase formation evaluation tool of
13. The single phase formation evaluation tool of
a distal end and a proximal end;
an axial bore;
a narrowed diameter section at said distal end; and
a release plug inserted into said axial bore at said proximal end.
14. The single phase formation evaluation tool of
said plunger additionally has an outer circumference and further comprises:
at least one O-ring located at said outer circumference; and
said outer circumference of said plunger is provided with threads for attachment to said axial bore of said piston.
15. The single phase formation evaluation tool of
16. The single phase formation evaluation tool of
17. The single phase formation evaluation tool of
a case adaptor positioned at said open bottom end of said formation fluid sample bottle; and
wherein said end cap is fixed to said case adapter.
18. The single phase formation evaluation tool of
19. The single phase formation evaluation tool of
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This application claims the benefit of U.S. Provisional Application 60/406,619, filed Aug. 27, 2002.
This invention relates generally to formation fluid testing and collection apparatus and more particularly to a single phase collection apparatus for a formation evaluation tool that collects formation fluids at a predetermined pressure and maintains the collected fluid pressure at such pressure throughout the sampling operation.
In the oil and gas industry, a drilling fluid (“mud”) is used during drilling of a wellbore to facilitate the drilling process and to maintain a hydrostatic pressure in the wellbore greater than the pressure in the formations surrounding the wellbore. This drilling fluid penetrates into or invades the formations for varying radial depths (referred to generally as the invaded zones) depending upon the types of the formation and drilling fluid used. Wireline formation testing tools lowered into the mud of the wellbore are used to monitor formation pressures, collect formation fluid samples from the wellbore and to predict performance of reservoirs around the wellbore. These formation evaluation tools typically contain an elongated body having an elastomeric packer that is sealingly urged against the zone of interest in the wellbore. Fluid is collected and brought to the surface for analysis to determine the properties of the fluids and the conditions of the zones or formations from where the fluids have been collected. During this process, it is critical that only uncontaminated fluids are collected, and in the same condition in which they exist in the formation.
Formation evaluation tools typically collect formation fluid by transferring such fluids from a probe into a sample chamber. Prior art formation evaluation tools such as sequential formation testers and repeat formation testers used large collection chambers that varied in size from one to five gallons to collect samples. Samples were not pumped into the chamber, but were forced into the chamber by the hydrostatic pressure of the formation acting against the atmospheric pressure in the chamber. The problem with these chambers was that once opened at the formation zone, they would ingest not only the sample, but also surrounding mud, rocks and other contaminates. Current formation testing tools overcome this problem by first testing fluids from the desired formations or zones of interest to ensure that the fluid is substantially free of mud filtrates, and then collecting fluids by pumping formation fluid into one or more sample bottles associated with the tool.
Because of the great difference in pressure between the formation (hydrostatic) and the interior of the sample bottle (atmospheric), there is a possibility that the formation fluid pumped into the chamber will vaporize, or “flash,” due to a great decrease in pressure. In order to prevent or reduce the chances of the liquid vaporizing from a decrease in pressure, formation fluid is pumped into the chamber at a relatively slow rate. In addition, the tools are often equipped with restrictions to slow down the fluid flow rate into the chamber. Water cushions are also utilized to fill the chambers more uniformly. However, it is common for the collected single phase fluid to separate into a two phase sample containing vaporized gas. If the sample fluid pressure is reduced prior to arrival in the analysis lab, a lengthy procedure is required to recombine the sample back into a single phase as it was in situ. Additionally, asphaltenes are commonly present in the hydrocarbons and if the pressure in the chamber remains at a relatively low pressure, such asphaltenes tend to flocculate to form gel-type masses in the fluid. The flocculation process is substantially irreversible. Thus, it is desirable to withdraw and maintain the sample fluid at a pressure above the bubble point to maintain it in a single phase.
Additionally, the temperature difference between the surface elevation and the formation elevation can exceed several hundred degrees Fahrenheit. As the tool is retrieved, the chamber temperature drops, causing the pressure in the chamber to drop. This substantial pressure drop in the chamber can result in the pressure of the formation sample dropping below the bubble point, resulting in a multi-phase sample.
Attempts have been made to maintain the fluid sample in a single phase by applying a pressurized nitrogen charge against a sample piston located in the chamber. This forces the sample piston against the fluid sample to maintain its pressure at a sufficient level to prevent a phase change upon retrieval. However, this system is complex and requires the use of nitrogen at a pressure of over 20,000 psi. The danger and inconvenience of working with nitrogen at this extremely high pressure discourages its use.
The present invention addresses the above noted problems and provides a single phase collection apparatus in which collected formation fluid is maintained at a predetermined pressure above the bubble point to maintain the sample in a single phase. No water cushions are required to uniformly fill the chambers. The tool also automatically maintains the chamber pressure above the bubble point pressure during the entire sampling operation regardless of the change in the temperature surrounding the chamber.
The single phase collection apparatus of the present invention is therefore designed to maintain wellbore formation samples at a pressure above the bubble point as the sample is removed from the wellbore and is transported to a laboratory for analysis. By utilizing a nitrogen gas charge that acts against a sample piston, the sample is maintained at a pressure above the bubble point of the sample, thereby preventing the sample from separating into two phases. However, the nitrogen pressure utilized in this collection apparatus is significantly lower than the pressure used in existing single phase collection designs, and is therefore safer and easier to use. The amount of pressure present in a commercial nitrogen bottle generally will be sufficient to pre-charge the apparatus, without the need for nitrogen gas boosters to achieve the high pressures required.
The present invention modifies an existing Department of Transportation (“DOT”) exempt sample bottle, simplifying DOT approval. Utilization of sample bottles that can be shipped as freight improves sample quality because the sample does not need to be transferred for transport. The use of these currently available sample bottles also allows in-the-field modification of existing DOT sample bottles. No additional leak paths for the sample are introduced by the modification, unlike older Drill Stem Test single phase samplers that created multiple leak paths with sliding seals and port crossing seals that affected the reliability of the devices. In addition, unlike the older designs which were limited to sample sizes of around 400 to 500 cubic centimeters due to the complexity of the mechanism, the simplified new design allows for the acquisition of larger sample sizes that may be more than twice that of existing designs. This is because the new design does not have any valves to shift, fluid to port or any other items to complicate and use up formation sample space. In addition, the size of the sample can be changed as desired because the nitrogen pressure can be adjusted for each sampling operation. A higher initial pressure is used to retrieve a smaller sample.
The Single Phase Sample Collection Apparatus utilizes an existing sample bottle modified to allow for the introduction of pressurized nitrogen gas that acts against a sample piston of the device to maintain the sample at or above the bubble point of the sample. The collection apparatus utilizes the hydrostatic pressure present at the depth of the desired formation sample to compress the nitrogen gas “pre-charge” to the pressure of the formation sample, then maintains that pressure as the collection apparatus is removed from the wellbore.
The present invention single phase collection apparatus 20, as shown in
The sample piston 1 is preferably made of an alloy steel, but can also be constructed from stainless steel, corrosion resistant alloy metals or other material with the appropriate properties to withstand the temperatures, pressures and corrosive conditions associated with such a device.
The nitrogen charging piston 3 is preferably made of an alloy steel, but can also be constructed from stainless steel, corrosion resistant alloy metals or other material with the appropriate properties to withstand the temperatures, pressures and corrosive conditions associated with such a device. The nitrogen charging piston 3 is sized to fit precisely within the bore of sample bottle 10. Gases are prevented from escaping around the nitrogen charging piston 3 by the use of one or more O-ring seals fitted into grooves inscribed into the outside diameter of the piston. An anti-extrusion backup seal may be placed on the low pressure side of the seal to help improve the seal. The nitrogen charging piston 3 has an open axial bore 9 allowing for the communication of gas through the piston. A check valve 5 is located within the axial bore 9 of the nitrogen charging piston and controls gas communication through the piston, into and out of the nitrogen gas chamber 6. Check valve 5 could also be a different type of valve such as a manually operated open/closed valve. A plunger 7, with a narrowed diameter section, fits into nitrogen charging piston 3. The plunger 7 is preferably threaded to allow engagement with matching threads on the inside diameter of the axial bore 9. When the plunger 7 is fully inserted into the piston 3, the narrowed diameter section of the plunger 7 functions to open check valve 5. The plunger 7 has an axial bore running through it with a removable release plug 8 to close off the end of the axial bore. O-ring seals at the outside diameter of the plunger 7 prevent gases from escaping around the plunger.
A case adaptor 11 with anti-rotation lugs 12, fits into and locks into the end of the sample bottle 10, and engages nitrogen charging piston 3 when the piston is pushed up to the end of its stroke. When engaged, the anti-rotation lugs 12 prevent the nitrogen charging piston 3 from rotating with respect to the lower case adaptor 11 so that the plunger 7 may be rotated for insertion/removal. The end cap 4 is inserted into and engages the case adaptor 11. The end cap 4 comprises a port 15 that is open to hydrostatic pressure when the collector apparatus is inserted into a wellbore, thereby exposing the nitrogen charging piston 3 to hydrostatic pressure.
In order to collect a formation sample, the single phase collection apparatus 20 is assembled as shown in
The plunger 7 is then removed from the nitrogen charging piston 3 and a purge adapter 14, connected to a pressurized nitrogen supply, is inserted into the nitrogen charging piston 3, opening the check valve 5, as shown in
Once assembled and pre-charged, one or more of the single phase collection apparatus 20 is inserted into the multi-chamber section (“MCS”) of a formation evaluation tool to collect formation samples. As the tool is lowered down into the wellbore, the open port 15 of the end cap 4 is exposed to mud at hydrostatic pressure and the nitrogen charging piston 3 is forced upwards once hydrostatic pressure is greater than the initial nitrogen gas pressure, compressing the nitrogen gas within the nitrogen gas chamber 6 so that the pressure of the nitrogen gas equals the hydrostatic pressure, as in
When a sample is to be taken, the appropiate valve of the MCS is opened and the desired formation fluid is pumped into the collection chamber 2, thereby forcing both the sample piston 1 and the nitrogen charging piston 3 downward towards the case adaptor 11 as shown in
As the collection apparatus 20 is retrieved from the wellbore, the formation sample shrinks as the sample cools. However, the highly compressible nitrogen gas acting against the sample piston 1 maintains the pressure of the sample above the bubble point.
At the surface, a shipping end cap replaces the end cap 4 for transportation and storage. If cool temperatures are expected during shipping, additional fluid can be pumped in through the shipping end cap to compress the nitrogen further, thereby helping to maintain the sample at a high pressure.
The removal of the sample from the collection apparatus 20 is accomplished using conventional techniques to remove formation samples from a sample bottle. Thus, fluid is pumped in to the collection apparatus 20 to force the sample out of the collection chamber 2.
Ringgenberg, Paul D., Gilbert, Gregory N.
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| Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
| Aug 27 2003 | Halliburton Energy Services, Inc. | (assignment on the face of the patent) | / |
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