Wells – Processes – Sampling well fluid
Reexamination Certificate
2002-11-01
2003-12-30
Bagnell, David (Department: 3672)
Wells
Processes
Sampling well fluid
C166S167000, C175S099000
Reexamination Certificate
active
06668924
ABSTRACT:
BACKGROUND OF INVENTION
This invention relates generally to sampling formation fluid from a wellbore. More specifically, the invention relates to reducing the contamination present in a sampling operation thereby providing a cleaner sample of formation fluids.
The desirability of taking downhole formation fluid samples for chemical and physical analysis has long been recognized by oil companies, and such sampling has been performed by the assignee of the present invention, Schlumberger, for many years. Samples of formation fluid, also known as reservoir fluid, are typically collected as early as possible in the life of a reservoir for analysis at the surface and, more particularly, in specialized laboratories. The information that such analysis provides is vital in the planning and development of hydrocarbon reservoirs, as well as in the assessment of a reservoir's capacity and performance.
The process of wellbore sampling involves the lowering of a sampling tool, such as the MDT™ formation testing tool, owned and provided by Schlumberger, into the wellbore to collect a sample or multiple samples of formation fluid by engagement between a probe member of the sampling tool and the wall of the wellbore. The sampling tool creates a pressure differential across such engagement to induce formation fluid flow into one or more sample chambers within the sampling tool. This and similar processes are described in U.S. Pat. Nos. 4,860,581; 4,936,139 (both assigned to Schlumberger); 5,303,775; 5,377,755 (both assigned to Western Atlas); and 5,934,374 (assigned to Halliburton).
The desirability of housing at least one, and often a plurality, of such sample chambers, with associated valving and flow line connections, within “sample modules” is also known, and has been utilized to particular advantage in Schlumberger's MDT tool. Schlumberger currently has several types of such sample modules and sample chambers, each of which provide certain advantages for certain conditions.
“Dead volume” is a phrase used to indicate the volume that exits between the seal valve at the inlet to a sample cavity of a sample chamber and the sample cavity itself. In operation, this volume, along with the rest of the flow system in a sample chamber or chambers, is typically filled with a fluid, gas, or a vacuum (typically air below atmospheric pressure), although a vacuum is undesirable in many instances because it allows a large pressure drop when the seal valve is opened. Thus, many high quality samples are now taken using “low shock” techniques wherein the dead volume is almost always filled with a fluid, usually water. In any case, whatever is used to fill this dead volume is swept into and captured in the formation fluid sample when the sample is collected, thereby contaminating the sample.
The problem is illustrated in
FIG. 1
, which shows sample chamber
10
connected to main flow line
9
via secondary line
11
. Fluid flow from main flow line
9
into secondary line
11
is controlled by manual shut-off valve
17
and surface-controllable seal valve
15
. Manual shut-off valve
17
is typically opened at the surface prior to lowering the tool containing sample chamber
10
into a borehole (not shown in FIG.
1
), and then shut at the surface to positively seal a collected fluid sample after the tool containing sample chamber
10
is withdrawn from the borehole. Thus, the admission of formation fluid from flow line
9
into sample chamber
10
is essentially controlled by opening and closing seal valve
15
via an electronic command delivered from the surface through an armored cable known as a “wireline,” as is well known in the art. The problem with such sample fluid collection is that dead volume fluid DV is collected in sample chamber
10
along with the formation fluid delivered through flow line
9
, thereby contaminating the fluid sample.
It is, therefore, desirable to provide techniques for removing contamination from the downhole tool so that cleaner fluid samples may be captured. It is further desirable that such techniques apply to downhole tools with one or more sample chambers within the downhole tool, one or more sample chambers in the same sampling location within the downhole tool, and/or sample chambers located at any location in the downhole tool along the main flowline.
The present invention is directed to a method and apparatus that may solve or at least reduce, some or all of the problems described above.
SUMMARY OF INVENTION
The sample module can further comprise a second valve disposed in the first flowline between the second flowline and the third flowline, and the second flowline can be connected to the first flowline upstream of said second valve. The third flowline can be connected to the first flowline downstream of the second valve. There can also be a fourth flowline connected to the sample cavity of the sample chamber for communicating fluid out of the sample cavity. The fourth flowline can also be connected to the first flowline, whereby fluid preloaded in the sample cavity may be flushed out using formation fluid via the fourth flowline. In one particular embodiment, the fourth flowline is connected to the first flowline downstream of the second valve. A third valve can be disposed in the fourth flowline for controlling the flow of fluid through the fourth flowline. The sample module can be a wireline-conveyed formation testing tool. In exemplary embodiments of the invention the sample cavity and the buffer cavity have a pressure differential between them that is less than 50 psi. In other exemplary embodiments of the invention, the sample cavity and the buffer cavity have a pressure differential between them that is less than 25 psi and less than 5 psi.
An alternate embodiment comprises a sample module for obtaining fluid samples from a subsurface wellbore. The sample module comprising a sample chamber for receiving and storing pressurized fluid with a piston movably disposed in the chamber defining a sample cavity and a buffer cavity, the cavities having variable volumes determined by movement of the piston. A first flowline for communicating fluid obtained from a subsurface formation proceeds through the sample module along with a second flowline connecting the first flowline to the sample cavity. A third flowline is connects the first flowline to the buffer cavity of the sample chamber for communicating buffer fluid out of the buffer cavity. A first valve capable of moving between a closed position and an open position is disposed in the second flowline for communicating flow of fluid from the first flowline to the sample cavity. A second valve capable of moving between a closed position and an open position is disposed in the first flowline between the second flowline and the third flowline. When the first valve and the second valve are in the open position, the sample cavity and the buffer cavity are in fluid communication with the first flowline and therefore have approximately equivalent pressures. The sample cavity and the buffer cavity can have a pressure differential between them that is less than 50 psi, less than 25 psi or less than 5 psi.
In another embodiment, the invention is directed to an apparatus for obtaining fluid from a subsurface formation penetrated by a wellbore. The apparatus comprises a probe assembly for establishing fluid communication between the apparatus and the formation when the apparatus is positioned in the wellbore. A pump assembly is capable of drawing fluid from the formation into the apparatus via the probe assembly. A sample module is capable of collecting a sample of the formation fluid drawn from the formation by the pumping assembly. The sample module comprises a chamber for receiving and storing fluid and a piston slidably disposed in the chamber to define a sample cavity and a buffer cavity, the cavities having variable volumes determined by movement of the piston. A first flowline is in fluid communication with the pump assembly for communicating fluid obtained from the formation through the sample module. A seco
Bolze Victor M.
Brown Jonathan W.
Bagnell David
Gay Jennifer Hawkins
Jeffery Brigitte L.
Ryberg John J.
Salazar J. L. Jennie
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