Reduced contamination sampling

A sample module for obtaining fluid samples from a subsurface wellbore, comprising:

• a sample chamber for receiving and storing pressurized fluid;
• 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 through the sample module;
• a second flowline connecting the first flowline to the sample cavity;
• a third flowline connecting 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 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 disposed in the first flowline between the second flowline and the third flowline;
• and
• wherein 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.

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;
• a pump assembly for drawing fluid from the formation into the apparatus via said probe assembly;
• a sample module for collecting a sample of the formation fluid drawn from the formation by said pumping assembly, said sample module comprising:
• a chamber for receiving and storing fluid;
• a piston slidably disposed in said chamber to define a sample cavity and a buffer cavity, the cavities having variable volumes determined by movement of said piston;
• a first flowline in fluid communication with said pump assembly for communicating fluid obtained from the formation through the sample module;
• a second flowline connecting said first flowline to the sample cavity;
• and
• a first valve disposed in said second flowline for controlling the flow of fluid from said first flowline to the sample cavity;
• wherein when the first valve is in the open position the sample cavity and the buffer cavity are in fluid communication with the first flowline and thereby have approximately equivalent pressures.

A method for obtaining fluid from a subsurface formation penetrated by a wellbore, comprising:

• positioning a formation testing apparatus within the wellbore, the testing apparatus comprising a sample chamber having a floating piston slidably positioned therein so as to define a sample cavity and a buffer cavity;
• establishing fluid communication between the apparatus and the formation;
• inducing movement of fluid from the formation through a first flowline in the apparatus with a pump located down stream of the first flowline;
• establishing communication between the sample cavity and the first flowline, whereby the sample cavity and the first flowline have approximately equivalent pressures;
• establishing communication between the buffer cavity and the first flowline, whereby the buffer cavity and the first flowline have approximately equivalent pressures;
• removing buffer fluid from the buffer cavity, thereby moving the piston within the sample chamber;
• delivering a sample of the formation fluid into the sample cavity of the sample chamber;
• and
• withdrawing the apparatus from the wellbore to recover the collected sample.

A sample module for use in a tool adapted for insertion into a subsurface wellbore for obtaining fluid samples, said sample module comprising:

• a sample chamber for receiving and storing pressurized fluid;
• a piston slidably disposed in said chamber to define a sample cavity and a buffer cavity, the cavities having variable volumes determined by movement of said piston;
• a first flowline for communicating fluid obtained from a subsurface formation through the sample module;
• a second flowline connecting the first flowline to the sample cavity;
• a third flowline connecting the first flowline to the buffer cavity of the sample chamber for communicating buffer fluid between the buffer cavity and the first flowline;
• a first valve capable of moving between a closed position and an open position disposed in the second flowline for communicating flow of fluid from the first flowline to the sample cavity;
• a fourth flowline connected to the sample cavity of said sample chamber for communicating fluid out of the sample cavity;
• and
• wherein when the first valve is 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.

A sample module for obtaining fluid samples from a subsurface wellbore, comprising:

• a sample chamber for receiving and storing pressurized fluid;
• 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 through the sample module;
• a second flowline connecting the first flowline to the sample cavity;
• a third flowline connecting the first flowline to the buffer cavity of the sample chamber for communicating buffer fluid out of the buffer cavity;
• a fourth flowline connected to the sample cavity of said sample chamber for communicating fluid out of the sample cavity;
• a first valve capable of moving between a closed position and an open position 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 disposed in the first flowline between the second flowline and the third flowline;
• and
• wherein 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.

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;
• a pump assembly for drawing fluid from the formation into the apparatus via said probe assembly;
• a sample module for collecting a sample of the formation fluid drawn from the formation by said pumping assembly, said sample module comprising:
• a chamber for receiving and storing fluid;
• a piston slidably disposed in said chamber to define a sample cavity and a buffer cavity, the cavities having variable volumes determined by movement of said piston;
• a first flowline in fluid communication with said pump assembly for communicating fluid obtained from the formation through the sample module;
• a second flowline connecting said first flowline to the sample cavity;
• a flush flowline connected to the sample cavity of said sample chamber for communicating fluid out of the sample cavity;
• and
• a first valve disposed in said second flowline for controlling the flow of fluid from said first flowline to the sample cavity;
• wherein when the first valve is in the open position the sample cavity and the buffer cavity are in fluid communication with the first flowline and thereby have approximately equivalent pressures.

A method for obtaining fluid from a subsurface formation penetrated by a wellbore, comprising:

• positioning a formation testing apparatus within the wellbore, the testing apparatus comprising a sample chamber having a floating piston slidably positioned therein so as to define a sample cavity and a buffer cavity;
• establishing fluid communication between the apparatus and the formation;
• inducing movement of fluid from the formation through a first flowline in the apparatus with a pump;
• establishing communication between the sample cavity and the first flowline, whereby the sample cavity and the first flowline have approximately equivalent pressures;
• flushing out at least a portion of a fluid precharging the sample cavity by inducing movement of at least a portion of the formation fluid though flowlines leading into and out of the sample cavity;
• establishing communication between the buffer cavity and the first flowline, whereby the buffer cavity and the first flowline have approximately equivalent pressures;
• removing buffer fluid from the buffer cavity, thereby moving the piston within the sample chamber;
• delivering a sample of the formation fluid into the sample cavity of the sample chamber;
• and
• withdrawing the apparatus from the wellbore to recover the collected sample.

A downhole tool for sampling fluid from a subterranean formation, comprising:

• a sample tank having a piston slidably movable therein, the piston defining a sample cavity and a buffer cavity within the tank, the sample tank in selective fluid communication with the formation;
• a sample flowline for communicating fluid from the formation to the sample cavity;
• and
• a flushing flowline for flushing fluid from the sample cavity into the wellbore.

A method for obtaining fluid from a subsurface formation penetrated by a wellbore, comprising:

• positioning a downhole tool having a sample tank therein in the wellbore, the sample tank having a piston slidably positionable therein, the piston defining a sample cavity and a buffer cavity within the tank;
• establishing fluid communication between the sample cavity and the formation;
• establishing fluid communication between the buffer cavity and the wellbore;
• inducing movement of formation fluid from the formation through a first flowline to the sample cavity;
• flushing fluid from the sample cavity through a second flowline into the wellbore;
• and
• inducing movement of buffer fluid from the buffer cavity through a third flowline whereby the piston is moved within the sample chamber and a sample of the formation fluid is drawn into the sample cavity of the sample chamber.

A method of obtaining fluid from a subsurface formation penetrated by a wellbore, comprising:

• positioning a downhole tool in a wellbore, the tool having a sample chamber with a piston slidably positionable therein, the piston defining a sample cavity and a buffer cavity;
• establishing fluid communication between the formation, the sample cavity and the buffer cavity whereby pressure is equalized therebetween;
• flushing fluid from the sample cavity to the wellbore;
• terminating fluid communication with the buffer cavity;
• and
• inducing flow of fluid into the sample chamber whereby a sample is collected.