Sample chamber with dead volume flushing

Details Sample chamber with dead volume flushing Sample chamber with dead volume flushing

2000-11-14

2002-10-22

Bagnell, David (Department: 3672)

Wells

Processes

Sampling well fluid

C166S167000, C175S099000

Reexamination Certificate

active

06467544

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to formation fluid sampling, and more specifically to an improved formation fluid sampling module, the purpose of which is to bring high quality formation fluid samples to the surface for analysis, in part, by eliminating the “dead volume” which exists between a sample chamber and the valves which seal the sample chamber in the sampling module.
2. Description of the Related Art
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); U.S. Pat. Nos. 5,303,775; 5,377,755 (both assigned to Western Atlas); and U.S. Pat. No. 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 flow line
9
via secondary line
11
. Fluid flow from 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
16
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. To date, there arc no known sample chambers or modules that address this problem of contamination resulting from dead volume collection in a fluid sample.
To address this shortcoming, it is a principal object of the present invention to provide an apparatus and method for bringing a high quality formation fluid sample to the surface for analysis.
It is a further object of the present invention to provide a method and apparatus of flushing the dead volume fluid from a sample module prior to the collection of a fluid sample in a sample chamber within the sample module.
It is a further object of the present invention to utilize a controllable inlet and outlet fluidly connected to a sample cavity of a sample module to achieve dead volume flushing.
SUMMARY OF THE INVENTION
The objects described above, as well as various other objects and advantages, are achieved by a sample module for use in a tool adapted for insertion into a subsurface wellbore for obtaining fluid samples therefrom. The sample module includes a sample chamber for receiving and storing pressurized 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 provided for communicating fluid obtained from a subsurface formation through the sample module. A second flowline connects the first flowline to the sample cavity, and a third flowline connects the sample cavity to either the first flowline or an outlet port. A first valve is disposed in the second flowline for controlling the flow of fluid from the first flowline to the sample cavity, and a second valve is disposed in the third flowline for controlling the flow of fluid out of the sample cavity, whereby any fluid preloaded in the sample cavity may be flushed therefrom using the formation fluid in the first flowline and the first and second valves.
In a particular embodiment of the present invention, the sample module further includes a third valve disposed in the first flowline for controlling the flow of fluid into the second flowline. The second flowline of this embodiment is connected to the first flowline upstream of the third valve. The third flowline is connected to the sample cavity and to the first flowline, the latter connection being downstream of the third valve.
The present invention may be further equipped, in certain embodiments, with a fourth flowline connected to the buffer cavity of the sample chamber for communicating buffer fluid into and out of the buffer cavity. The fourth flowline is also connected to the first flowline, whereby the collection of a fluid sample in the sample cavity will expel buffer fluid from the buffer cavity into the first flowline via the fourth flowline. In some embodiments of the present invention, a fifth flowline is connected to the fourth flowline and to the first flowline, the latter connection being upstream of the connection between the first and second flowlines, the fifth flowline permitting manipulation of the buffer fluid to create a pressure differential across the piston for selectively drawing a fluid sample into the sample cavity. The fourth and fifth flowlines thus connect the buffer cavity to the first flowline both upstream and downstream of the third valve. When the present invention is so equipped with the fourth and fifth flowlines, manual valves are preferably positioned in these flowlines to select, uphole, whether the buffer fluid is communicated to the first flowline upstream of the third valve or downstream of the third valve.
The present invention may be further defined in terms of an apparatus for obtaining fluid from a subsurface formation penetrated by a wellbore, comprising a probe assembly for establishing fluid communication between the apparatus and the formation when the apparatus is positioned in the wellbore, and a pump assembly for drawing fluid from the formation into the apparatus via the probe ass

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