Transmission, Distribution, & Refining
Coiled Tubing Deployed Hard Rock Thermal Spallation Cavity Maker


Goal: The goal is to develop alternatives for natural gas storage in market areas where conventional storage options may be technically unfeasible.

Objectives: The objective is to develop a prototype drilling and cavity formation system for the rapid development and commercialization of deep, natural gas storage cavities in hard rock.

Coiled-tubing deployed spallation drill concept

Los Alamos National Laboratory (LANL) – Project management and design engineering
New Mexico Institute of Mining and Technology (NM Tech)y – Equipment design, fabrication and testing


  • Reviewed and summarized earlier work on spallation,
  • Developed a flame-jet burner design concept,
  • Developed a reeled drill stem design concept based on off-the-shelf coiled tubing, with a manifold to conduct air, cooling water, fuel and telemetry cable into the reel end of coiled tubing while maintaining a separation of air and fuel,
  • Performed preliminary calculations to model system performance,
  • Demonstrated preliminary prototype burners,
  • Performed spallation tests on rock samples using a prototype burner,
  • Began coding of a program designed to control fuel/air mixture during ignition and operation,
  • Designed and procured a coiled-tubing drill stem that incorporates multiple internal conduits, and
  • Conducted tests to determine the feasibility of generating ignition sparks downhole using conventional spark plugs.
The approach is to adapt present spallation technology to use coiled-tubing deployed drilling equipment to produce large cavities at the bottom of deep vertical bores in a hard rock formation.

Thermal spallation drilling also called flame-jet drilling, is a method of creating holes and cavities in some hard rocks that are expensive to drill using traditional mechanical (rotary and percussion) drilling methods. A hydrocarbon fuel and air are burned in a flame-jet burner to produce a high velocity exhaust that is applied to the rock surface on the bottom of the hole. The rapid heating of the rock creates a large thermal gradient, which in turn produces high compressive stresses on the surface of the exposed rock, leading to surface layer buckling wherever rock flaws in the near surface material provide a nucleation point for the creation of free surface.

Commercial application of thermal spallation of hard rock has been limited to shallow drilling for blast holes in surface mining and for quarrying. Several efforts to develop a deep drilling capability based on thermal spallation demonstrated technical feasibility but failed to produce commercial interest. Challenges included the following: (1) many rock materials do not spall readily, (2) system designs required conduits for fuel, air, cooling water and an electric power cable to energize a downhole igniter system, as well as a return flow stream of exhaust, steam, and rock spalls, (4) early demonstrations were plagued by flameouts while drilling in addition to interruptions caused by drill stem connections required to extend the reach of the drill, and (5) the specific energy required to produce hole volume is between one and two orders of magnitude greater for thermal spallation than for either rotary or percussion drilling. Nonetheless, spallation might be the only option for producing cavities in hard rock in areas where gas storage is needed but conventional storage reservoirs are unavailable.

The major thrust of this project was to adapt a flame-jet burner assembly to operate on the bottom of a coiled tubing drill string to produce a practical deep-hole spallation drill and cavity former. A reeled tubing drill stem will allow the flame-jet drilling system to operate continuously until the drill reaches total design depth or the cavity chamber is completed.

The critical elements of the prototype needed for a pre-commercial demonstration include:

  • A flame-jet burner assembly,
  • A burner supply and control system that automatically supplies fuel air and cooling water to the burner assembly,
  • A coil tubing connector that mates the downhole burner (including the supply and control functions) assembly to the coiled-tubing drill stem,
  • A reeled drill stem with internal utilities that provides an uninterrupted supply of fuel, air, and coiling water to the burner, and a cable with telemetry and electric power conductors needed to support downhole sensors, controllers, and a downhole flame igniter.
Early prototypes of design concepts for each of these elements have been fabricated and preliminary tests have been conducted. A working system capable of excavating a hole has not yet been demonstrated.

Current Status (June 2005):
This project was funded under the National Lab Partnership Program for Oil & Gas Technologies. NETL support for this project ended at the conclusion of the Phase I work plan when the DOE terminated Oil & Gas Partnership funding. An interim report detailing the Phase I results is available below under "Additional Information".

Project Start: September 1, 2002
Project End: June 30, 2005

Anticipated DOE Contribution: $350,000
Performer Contribution: $0

Contact Information:
NETL – Gary Sames ( or 412-386-5067)
LANL – Donald Dreesen ( or 505-667- 1913)

Additional Information 
Phase 1 Final Report [PDF-1.115MB]