Pressure compensated locking sampling tool

A method for sampling wellbore fluid, comprising:

• lowering a sampling tool into a wellbore, the sampling tool comprising a sampling chamber, a pressurized chamber, a sampling rod partially disposed in the sampling chamber and partially disposed in the pressurized chamber, and a locking mechanism disposed between sampling chamber and the pressurized chamber;
• opening the sampling chamber, wherein opening the sampling chamber comprises moving the sampling rod to a first position to open fluid communication between the wellbore and the sampling chamber, and wherein when the sampling rod is in the first position:
• fluid communication between the pressurized chamber and the sampling chamber is blocked;
• a bore extending through the sampling rod is in fluid communication with the sampling chamber through a first opening in the sampling rod;
• and
• the locking mechanism is in a first configuration retaining the sampling rod in the first position;
• retrieving a sample of a wellbore fluid;
• closing the sampling chamber, wherein closing the sampling chamber comprises moving the sampling rod to a second position to close fluid communication between the wellbore and the sampling chamber, and wherein when the sampling rod is in the second position:
• fluid communication between the pressurized chamber and the sampling chamber is permitted, wherein permitting the fluid communication between the pressurized chamber and the sampling chamber includes opening fluid communication from the pressurized chamber, through a second opening in the sampling rod, into the bore of the sampling rod, out of the first opening in the sampling rod, and into the sampling chamber;
• and
• the locking mechanism is in a second configuration retaining the sampling rod in the second position;
• and
• pressurizing the sample of fluid from the wellbore with a pressurized fluid from the pressurized chamber.

A wellbore fluid sampling tool, comprising:

• a sampling chamber in selective fluid communication with a pressurized chamber;
• a sampling rod disposed in the tool, the sampling rod including a bore, a first opening extending between an outer surface of the sampling rod and the bore, and a second opening extending between the outer surface of the sampling rod and the bore, wherein the sampling rod is movable between a first position and a second position, and wherein, in the first position:
• the sampling chamber is open to wellbore fluid;
• fluid communication between the sampling chamber and the bore of the sampling rod is open through the first opening;
• and
• fluid communication between the chambers is closed;
• and
• wherein, in the second position:
• the sampling chamber is closed to wellbore;
• and
• fluid communication is opened from the pressurized chamber, through the second opening in the sampling rod, into the bore of the sampling rod, out of the first opening in the sampling rod, and into the sampling chamber;
• and
• a sampling rod locking mechanism disposed between the chambers, wherein in a first locking position the sampling rod is retained in the first position, and in the second locking position, the sampling rod is retained in the second position.