Method and apparatus for formation sampling during the drilling of a hydrocarbon well

A tool for obtaining samples of the earth surrounding a wellbore, comprising:

• a sub, having ends for coupling within a drill string, said sub having a mandrel along an exterior surface;
• a gun assembly disposed within said mandrel, comprising:
• a sampling bit;
• and
• a charge coupled to said sampling bit, for firing said sampling bit in an outward direction from said sub;
• an electronic unit located in said sub, for controlling said gun assembly responsive to a remote signal;
• and
• a measurement-while-drilling sub, comprising a plurality of transducers for measuring formation parameters at a downhole location, coupled in series with said drill string, said sub, and said drill bit.

A method for obtaining samples of the formation from the sidewalls of a wellbore, comprising:

• assembling a tool comprising a sub having first and second ends for coupling within a drill string and having a mandrel along an exterior surface, said mandrel having an open cross-section extending to the first end of said sub, by sliding a gun assembly into said mandrel from the first end of said sub, said gun assembly comprising:
• a housing, having a size and shape allowing it to be inserted into said mandrel from the first end of said sub;
• a plurality of sampling bits disposed within said housing;
• and
• a plurality of charges, each coupled to one of said plurality of sampling bits;
• coupling said sub within the drill string near a drill bit;
• drilling a wellbore with the drill bit;
• activating one of said plurality of charges to fire its associated sampling bit into the formation adjacent said sub;
• withdrawing said drill string and sub from said wellbore, so that the sample of the formation obtained by said sampling bit after the activating step may be analyzed;
• detaching the first end of the sub from the drill string;
• and
• slidably removing the gun assembly from the mandrel in said sub.

A method for obtaining samples of a formation from the sidewalls of a wellbore, comprising:

• drilling a wellbore with a drill bit coupled to the distal end of a drill string from the surface, said drill string including a tool coupled within said drill string, and located near said drill bit, said tool comprising:
• a sub, having ends for coupling within a drill string, said sub having a mandrel along an exterior surface;
• a gun assembly disposed within said mandrel, comprising:
• a sampling bit;
• and
• a charge coupled to said sampling
• monitoring formation parameters during said drilling step;
• activating said charge to fire the sampling bit into the formation adjacent said sub, responsive to the results of said monitoring step;
• and
• withdrawing said drill string and sub from said wellbore, so that the sample of the formation obtained by said sampling bit after the activating step may be analyzed.