Drilling system with an acoustic measurement-while-driving system for determining parameters of interest and controlling the drilling direction

A drilling assembly for use in drilling of a wellbore, comprising:

• (a) a drill bit at an end of the drilling assembly for drilling the wellbore;
• (b) an acoustic device having a transmitter for transmitting acoustic signals at a first frequency and a second frequency in the wellbore during drilling of the wellbore and a receiver for detecting signals transmitted by the transmitter;
• (c) a processing system associated with the drilling assembly for processing signals from the receiver at the first frequency for determining an acoustic velocity of a formation surrounding the wellbore and at the second frequency for determining a travel time from the drilling assembly to a subsurface reflection point;
• and
• (d) a steering device disposed in the drilling assembly for altering direction of drilling the wellbore by the drill bit.

A downhole tool for use in drilling of a wellbore in a formation, comprising:

• (a) a first acoustic sensor arrangement including at least one transmitter and at least one acoustic receiver for providing signals indicative of acoustic velocity of a formation surrounding the wellbore;
• (b) a second acoustic sensor arrangement including a transmitter and a pair acoustic receivers substantially symmetrically disposed about the transmitter for providing a pair of signals indicative of a first position of the downhole tool relative to a subsurface bed boundary in the formation;
• and
• (c) a processor for
• (i) determining an acoustic velocity of the formation from the first acoustic sensor arrangement, and
• (ii) determining the first position of the downhole tool relative to the subsurface bed boundary from the determined acoustic velocity and the pair of signals from the second acoustic sensor arrangements.

A drilling assembly for use in drilling of a wellbore, comprising:

• (a) a drill bit at an end of the drilling assembly for drilling the wellbore;
• (b) a first acoustic sensor arrangement including at least one transmitter and at least one acoustic receiver for providing signals indicative of acoustic velocity of a formation surrounding the wellbore;
• (c) a second acoustic sensor arrangement including a transmitter and a pair acoustic receivers substantially symmetrically disposed about the transmitter for providing signals indicative of a first position of the downhole tool relative to a subsurface bed boundary;
• and
• (d) a processor for:
• (i) determining an acoustic velocity of the formation from the first acoustic sensor arrangement, and
• (ii) determining the first position of the downhole tool relative to the subsurface bed boundary from the determined acoustic velocity and signals from the second acoustic sensor arrangements, and
• (iii) controlling a steering device disposed in the drilling assembly to alter the direction of drilling of the wellbore by the drill bit in response to said determined first position.

A method of drilling a borehole in a formation utilizing a downhole tool having a first and second acoustic sensor arrangements during drilling of the borehole, comprising:

• (a) conveying the downhole tool in the borehole;
• (b) using the first sensor arrangement to provide signals indicative of the acoustic velocity of the formation;
• (c) using a transmitter in the second sensor arrangement to transmit acoustic signals into the formation;
• (d) detecting acoustic signals reflected by a subsurface bed boundary by a pair of acoustic receivers disposed substantially symmetrically about the transmitter in the second sensor arrangement;
• (e) using the processor to determine the acoustic velocity of the formation from the signals provided by the first sensor arrangement;
• and
• (f) using the processor to determine a position of the subsurface bed boundary in the formation from the determined acoustic velocity and the signals detected by the pair of acoustic receivers.