Hammer Drill System

Hammer Drill tests were performed by SDS Digger Tools, PTY. LTD. of Canning Vale, Australia. These field tests were successfully completed in early August of this year as part of Phase I of the Hammer Drill project. Results from this testing program were encouraging and have resulted in ODP/TAMU recommending that the development of a larger hammer be pursued.

The primary objectives in the initial tests were to determine whether the hammer and bit combination would spud on high inclination slopes and whether casing could be drilled in at the same time as the hole was being drilled. Both of these objectives were satisfied during the field testing program (see photographs).

It was hoped that holes could be spudded at angles of 15-30 degrees to simulate what had been encountered at hard rock locations similar to those at MARK, EPR and other spreading ridge centers. The actual results of spudding with the hammer/bit combination were above expectations. The two part bit successfully started holes at angles of 15-45 degrees. Seven tests were performed with each attempt resulting in a hole being started in the black granite test piece. The bit was operated both with and without the outer casing shoe portion of the bit.

The second portion of Phase I was to drill in 7" casing with the SDS 4¾" water hammer using the same 7½" two- part center bit tested during the inclination work. This 4¾" water hammer was initially designed for bits of 5½" diameter. Even though the water hammer was not the optimum size for the bits being tested, SDS agreed to perform the tests with the existing "off the shelf" hammer. This tested the hammer at a lower efficiency than a custom designed hammer for the size of bit being drilled. The test resulted in ODP/TAMU being able to assess if the hammer worked as claimed by the vendor without a large capital outlay for a custom design during this initial phase. The test also provided SDS the opportunity to see how far the envelope could be pushed using larger sized bits with an existing hammer.

The second half of the field testing program entailed actually driving-in casing. Originally, two 20+ m drill-in casing holes were planed to be performed. In actuality, only one 21 m hole was achieved. The results in achieving less than the proposed program plan were due to ancillary equipment and drill-water supply problems at the remote quarry site and not due to inadequate hammer performance. The hammer did perform as designed, despite the fact that it was being asked to drill a larger hole than it was originally designed to accommodate. The average rate of penetration with the 4¾" hammer drilling a 7½" hole was 3.72 m/hr. Rates as high as 7.35m/hr were recorded during the tests. Based on the results of the water hammer and bit tests, ODP/TAMU has recommended that the next Phase of the project be initiated.

Currently ODP/TAMU is discussing several options for Phase II of the Hammer Drill project with SDS Digger. In the original contract, a larger sized hammer was to be built if the prototype testing was successful. These hammers were envisioned to be capable of drive-in 16" casing. Since that time, SDS has designed and begun to manufacturing three 12¼" hammers for a different project. The project for which these hammers were produced has been delayed. Therefore, SDS has offered them to ODP/TAMU. Since the objective of hammer casing project for Leg 179 is to test the hardware by driving casing from the surface into hard rock, it really does not make much difference whether this is demonstrated with 13 3/8" or 16" casing at this time. There is a considerable cost difference between these different size hammers and the associated hardware to support the larger hammers. Consequently, it is felt that the selection of the 12¼" at this time is a more prudent decision based on the available funds and manpower available within ODP/TAMU.

There are still some technical and contractual hurdles which will have to be cleared, but two 12 prototype hammers are available for testing during Leg 179. Also, one eccentric, and one retractable bit will be used with the hammer. Casing will be suspended from the top of the drill string.

Technical issues which are yet to be resolved are

weight on bit requirements;
level and magnitude of field test prior to going to sea; and
flow rate and pressures obtainable from the current mud handling system on the JOIDES Resolution to support the size of hammer selected for Phase II. Determinations will be made during the Panama port call.
(See (Technology and Engineering Development Committee (TEDCOM).)
Note: At the December 1996 PCOM meeting it was decided to postpone the Hammer Drilling to Leg 179 (formerly scheduled for Leg 174B). This allows the saving of 10 days from the 1997 schedule providing 2 days for the extension of the Halifax port call and bringing the schedule after leg 174B forward by 8 days. Bringing the schedule forward was necessary to allow the ship to leave the Antarctic Peninsula area by the end of March 1998 (the end of the good weather window). The Kerguelen leg will start in early-mid December 1998.