The invention relates to horizontal directional drilling and, in particular, to improvements in bottom hole assemblies for such drilling techniques.
Horizontal directional drilling methods are well known and can offer many advantages over traditional open trench digging operations. There remains a need for greater precision in monitoring and guiding the course of the hole as it is being bored. This need is particularly acute in utility easements and like corridors where pre-existing lines are located often without precision in their placement and xe2x80x9cas builtxe2x80x9d records.
As used herein, the terms xe2x80x9csondexe2x80x9d and xe2x80x9cmonitoring/tracking devicexe2x80x9d are used interchangeably to mean a device known in the trenchless boring industry as a surveying device for the monitoring and tracking of a bore hole. The term xe2x80x9cboring devicexe2x80x9d refers to equipment such as a rock tricone drill bit, a poly-diamond-crystalline (PDC) bit, or any other device known in the art to drill or lengthen a bore hole. Finally, the terms xe2x80x9centrenching powering devicexe2x80x9d and xe2x80x9cmud motorxe2x80x9d are used interchangeably for a device generally known in the art used to rotate a boring device, without turning the drill pipe/drill string, by some type of drilling rig to continue a hole or bore.
Known horizontal directional drilling bottom hole assemblies typically include a sonde that transmits electromagnetic signals indicating the pitch (from horizontal), the clock (roll about a horizontal axis clockwise or counterclockwise from a reference of say 12 o""clock), and the depth of the sonde. The sonde also enables a person sweeping the corridor with a receiver or detector to locate the horizontal or lateral position of the sonde in the specified corridor.
Because of limitations of current tooling, the transmitter/guidance system or sonde is ordinarily located a considerable distance away from the boring device when an entrenching powering device is used. The sonde may only be as close as about 20 feet and as far as about 50 feet from the boring device. This is due to the fact that an entrenching powering device has generally not been designed to integrate a sonde. The distance between the sonde and the boring device is a major concern for drillers in the utility business, especially when they encounter a job with very restrictive parameters in terms of drilling path.
The sonde transmits a signal that indicates where the sonde is located which can be 20 feet+behind the boring device. This type of drilling has been described as driving a car forward, from the back seat looking out the rear window. A driller only xe2x80x9cseesxe2x80x9d where he has already drilled, not where he is currently drilling. This becomes a major problem if the boring device veers off course and begins boring outside a designated corridor. The operator will not know there is a potential problem until the boring device is 20 feet+off course. If the driller waits longer to see if the boring device steers back on course, the boring device may continue even further off course. This causes a risk that the driller may destroy cable lines, gas lines, or the like and if such destruction occurs it is not only expensive but dangerous as well.
The invention provides an improved bottom hole assembly for horizontal directional drilling in which the sonde is carried ahead of the power section of the entrenching powering device or mud motor. In a presently preferred embodiment, the sonde is located in a pocket formed in the wall of a housing of the entrenching powering device that surrounds a bearing mandrel or bit driving shaft. More specifically, the sonde receiving pocket is nestled axially between thrust bearings supporting the mandrel and a flex shaft transmission that couples the power section to the mandrel. This forward location of the sonde greatly improves the accuracy of surveying while boring the hole so as to facilitate placement of the hole and ultimate line in the intended path.
The disclosed mounting arrangement for the sonde readily allows the sonde to be adjusted for a proper clock orientation and is somewhat resilient to limit vibrational forces transmitted to the sonde during operation.
Other mounting structures for the sonde are disclosed. Each of these structures offers improved boring accuracy over prior art constructions by enabling the sonde to be positioned relatively close to the boring device.