Abstract: An excavation system for forming a wellbore through a subterranean formation, the system employing pressurized drilling fluid with impactors mixed therein. The pressurized fluid with impactors is directed to a drill string having a drill bit with nozzles on its lower end. The fluid impactor mixture is discharged from the nozzles and against the formation, wherein the impactors contact, compress, and fracture the formation to excavate through the formation. The system includes an impactor injection system that injects impactors into a stream of pressurized drilling fluid to form the mixture. The injection system operates at substantially the same pressure as the pressurized drilling fluid.

Abstract: A method and system of subterranean excavating that estimates a buoyancy force applied to a downhole excavating system from drilling fluid. The estimated buoyancy force is used to derive a true weight on bit (WOB) at the borehole bottom. The derived realized WOB is compared to a target WOB to obtain a change in WOB. Based on the change in WOB, the excavating system is adjusted so the realized WOB approximates the target WOB. The excavating system adjustment includes applying a compensating force to the string. Compensating forces can be produced by manipulating a block assembly or deploying a thruster device in the string.

Abstract: A method and system of subterranean excavating that estimates a buoyancy force applied to a downhole excavating system from drilling fluid. The estimated buoyancy force is used to derive a true weight on bit (WOB) at the borehole bottom. The derived realized WOB is compared to a target WOB to obtain a change in WOB. Based on the change in WOB, the excavating system is adjusted so the realized WOB approximates the target WOB. The excavating system adjustment includes applying a compensating force to the string. Compensating forces can be produced by manipulating a block assembly or deploying a thruster device in the string.

Abstract: An excavation system for forming a wellbore through a subterranean formation, the system employing pressurized drilling fluid with impactors mixed therein. The pressurized fluid with impactors is directed to a drill string having a drill bit with nozzles on its lower end. The fluid impactor mixture is discharged from the nozzles and against the formation, wherein the impactors contact, compress, and fracture the formation to excavate through the formation. The system includes an impactor injection system that injects impactors into a stream of pressurized drilling fluid to form the mixture. The injection system operates at substantially the same pressure as the pressurized drilling fluid.