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Optimization of Mud Hammer Drilling Performance
Project Number

The goal is to improve the depth rating and efficiency of percussion drilling in hard rock formations by: benchmarking the performance of a several commercial fluid drilling hammer, recommending ways to improve a fluid hammer performance, and facilitating industrial acceptance and commercialization.

Diagram of a downhole/mud hammer
Diagram of a downhole/mud hammer



Terra Tek, Inc. – Project management and all research products

Salt Lake City, Utah 84101


Downhole fluid hammer systems convert a portion of the power resident in the drilling fluid to mechanical force that drives the drill bit into the formation. While several downhole hammer tools are currently available for boreholes where air is employed as the drilling fluid, the application of hammer drilling using liquids at high or even moderate borehole pressures has experienced problems. If this technology can be more effectively developed, these so-called “mud hammers” could be especially useful in drilling into hard rock formations found in deeper basins.

This project brings together a team of industry advisors/specialists to focus on three study areas in a controlled drilling test environment to determine the potential and best course of action for successful mud hammer commercialization. The study areas are: large-scale laboratory hammer drilling tests at reservoir conditions, benchmarking of hammer performance relative to conventional drilling, and optimization of hammer performance. Additionally a task was initiated under this project to study the effect of impact cutters on destroying a rock mass. Industry has shown significant interest in the impact tests. These impact tests were conducted to extend the understanding through basic research as to the rock breakage and cuttings removal under the dynamic loading conditions of hammer drilling.

The original industry partners for this project were SDS Digger Tools, Novatek, BP Amoco, ExxonMobil, and Pajarito Enterprises. Subsequently, PDVSA, Shell, ConocoPhillips, and Smith International have become participants.

Full-scale drilling optimization tests were performed in TerraTek’s wellbore simulator, where confining and overburden stresses are applied to the rock samples and borehole pressure is established by choking the drilling fluid flow downstream of the bit. Weight on bit is applied with a servo-controlled system. Rotary speed is controlled with variable speed direct drive motors, five-speed transmission, and a standard oil-field rotary table. The samples were 15 ½ inches wide by 36 inches long, Carthage marble and Crab Orchard sandstone, with unconfined strengths of approximately 16,000 psi and 27,000 psi, respectively. Two water-based muds (10 and 15 ppg) and 9 ppg brine were used as drilling fluids.


The results will be used to improve the state of mud hammer drilling at depth and improve the understanding and ability to use mud hammers at deeper depths and at higher wellbore pressures. This knowledge is helping to redesign percussion drilling tools which have shown to drill much faster at shallower depths and lower wellbore pressures. Increasing the rate of penetration will reduce risks, drilling time and costs as well as increasing drilling efficiency, thus reducing the environmental impact of the drilling process.


  • Demonstrated the ability of three fluid hammer systems to operate under environments of high wellbore pressures and heavy mud weights;
  • Determined that fluid hammers can be optimized to provide better performance at higher pressure and identified features in need of quantitative research;
  • Instigated a more robust design for industrial hammers;
  • Current mud hammer designs have a limitation of about 3,000 psi Wellbore pressure (approximately 6,000 feet at 10 ppg);
  • Deep-well laboratory full-scale drilling (and field tests) with mud hammers have shown that penetration rates appear to be at best equal to rates from roller or fixed cutter bits;
  • To make hammer drilling viable at higher pressures improvements based on fundamental understanding of rock breakage and chip removal under impact loading is required;
  • Effective blow energy necessary to create a rock deformation or chip formation force (DCF) is limited. Energy or impacts greater than the DCF force is wasted energy and better use of energy can be made by increasing the frequency of blows.

TerraTek completed 13 drilling tests in 2001 with the SDS Digger Tools Hydra 185 hammer, the Novatek 7 ¾-inch hammer, and a conventional 8 1/2-inch rollercone rock bit. Overall, the two hammers functioned properly at simulated borehole pressures of up to 3,000 psi with weighted, water-based mud. Rate of penetration performance was found to decrease with increasing wellbore pressures. SDS and Novatek gained considerable experience on the operation of their tools at simulated depth conditions. Optimization of the tools has begun as a result of these first tests. In 2002, Smith International participated in benchmark testing of its seven-inch hammer bit.

A “cutter impact testing” program examined rock removal under conditions that could offer additional insights into fluid hammer performance optimization. The focus of this work was on single cutter impact testing in pressurized mud (up to 5000 psi) and at elevated pore pressure, to better understand the cutter/rock interaction. The impact energy and duration of impact were varied to evaluate the effect of the shape of the stress wave that enters the rock sample. The performance of the cutter was evaluated by measuring the crater volume, energy partitioning, and if possible, the extent of the damaged zone under the crater. A paper was published on the results of the impact testing.

Current Status

This project is complete.

Project Start
Project End
DOE Contribution


Performer Contribution


Contact Information

NETL – Gary Covatch ( or 304-285-4589)
Terra Tek – Arnis Judzis ( or 801-584-2483)

Additional Information

2002 Topical Report [PDF-7606KB]

Pertinent Publications:
IADC/SPE 74540 "World's First Benchmarking of DrillingMud Hammer Performance at Depth Conditions." Authors - Tibbitts/Judzis/Black, TerraTek; Roy Long, DOE; Brian Miller, BP America

"Mud Hammer Performance Optimization", GTI Natural Gas Technologies II Conference 8-11 February 2004, Arizona Authors - Alan Black and A. Judzis, TerraTek

"Mud Hammers Changing the Game", Drilling, March 2003, pgs 16-18, Author - Wajid Rasheed.

Green, S,. Judzis, A., Curry, D. , Black, A., Prasad, U., and Rogers, J: “Single Cutter Impact Tests Investigate Deep-Well Hammer-Drilling Performance,” paper SPE 97173 presented at the 2005 SPE Annual Technical Conferences and Exhibition 9-12 October 2005.