The attraction of microhole drilling is the prospect of greatly reducing the cost of drilling shallow- and moderate-depth holes for exploration, field development, long-term subsurface monitoring, and to a limited degree, actual oil and gas production. If the costs of these activities can be reduced, oil and gas reservoirs that are uneconomic to produce today could become economically viable in the future.

Microhole technology holds great promise for economically recovering a sizeable portion of the estimated remaining shallow (less than 5,000 feet subsurface) oil resource in the United States. The DOE estimates this targeted shallow resource to be over 200 billion barrels, and recovering just 10 percent would be equal in volume to 10 years of OPEC oil imports at current rates.

MORE INFO Read about DOE's first microhole R&D project selections

In 2003, after earlier exploratory research principally conducted by the Los Alamos National Laboratory, the U.S. Department of Energy's Office of Fossil Energy began placing additional emphasis on microhole technology. The Energy Department envisions microholes with diameters as small as 1 to 2 inches, from 1/25th to 1/50th the cross-sectional area of conventional wells.

Microhole drilling systems will bore oil and gas wells diameters much smaller than conventional wells.

When holes this small are used for exploration - for example, to locate the best prospects for producing natural gas from coal beds - it may be possible to reduce drilling costs by a third or more. When used for field development, microholes may be less than half as expensive as conventional wells. Smaller diameter boreholes and drilling rigs mean less surface disturbance.

Savings in drilling costs result from smaller drill sites, much smaller draw-works for pipe and tube handling, greatly reduced materials for drilling and well completion, less waste to handle and dispose, and fewer support personnel.

Some of the specific advantages of microhole drilling are:

• Equipment is smaller (microdrilling systems could occupy a space roughly 1/20th that of a typical rig) and weighs less (less than one tenth as much) as conventional systems reducing equipment costs (by up to 90 percent) and manpower to operate equipment.
  
• Materials required for drilling and well completion are reduced.
  
• Coiled tubing saves time and money because it requires fewer trips in and out of the wellbore than conventional drilling techniques.
  
• Volumes of drilling fluids and cuttings can be reduced by one-fifth, reducing disposal costs.
  
• Drill rigs and associated equipment have smaller footprints, reducing environmental impact and making the system particularly advantageous when operating in environmentally sensitive areas.

In fact, the idea of drilling holes as small as 1-inch in diameter is not new. Relatively deep holes with diameters as small as 1.175-inch have been drilled using mining coring rigs for at least 50 years. Small diameter coiled tubing is readily available.

The technological challenge to microhole technology will be to develop an entire drilling system. Suitable drill bits and pipes are available today, but subsurface sensors, motors, logging tools, and other borehole instruments small enough to fit into the micro-wellbores and rugged enough to withstand the rigors of underground environment must still be developed.

The Los Alamos Concept

The basic microdrilling rig concept developed by Los Alamos National Laboratory in the mid-1990s (shown in the drawing above) integrated microhole technology with coiled-tubing technology.

A coiled-tube drilling system uses a long, continuous length of pipe wound on a spool. The pipe is straightened prior to pushing into the wellbore and recoiled to spool the pipe back onto the transport and storage spool. The petroleum industry has begun using coiled-tubing in some instances to drill lateral boreholes off of a horizontal well to increase a well's productivity, and in other cases, for well cleanouts.

The microdrilling rig developed by Los Alamos was a highly automated drilling system, capable of being operated by a two-person crew. This avoided the more complicated and labor-intensive aspects of conventional oil field drilling.

In the late 1990s, Los Alamos' coiled-tubing microdrilling concept evolved from theoretical studies to three successful field demonstrations involving 1-3/4 and 2-3/8 inch diameter holes drilled to depths of 700 feet.

MORE INFO The Los Alamos Microhole Technology Roadmap [4.3MB PDF]

To meet the Energy Department's target of a low-cost, high performance microhole system capable of moderate depths on the order of 5,000 feet, the Los Alamos experiments revealed that some new technology development will be required, specifically:

• Drilling hydraulics, cuttings transport, and bore-wall stabilization will have to be optimized.
• Drilling motors and rotary percussion hammers with compatible isolation tools will have to be enhanced.
• Downhole sensors, instrumentation, and telemetry needed to support automated drilling, real-time steering, and logging-while-drilling will have to be significantly downsized.

Commercial Prospects

Microholes may not be used, at least initially, as actual production wells. However, they may be ideal for probing new reservoir prospects to determine the presence of hydrocarbons, or for drilling between existing wells in older fields to locate oil or gas that might have been bypassed previously ("infill drilling"). Microholes could be used for directional drilling, underbalanced drilling, formation testing, drilling shallow development wells, and drilling deep exploration holes. They could also be used to place sensors in or near a reservoir for data monitoring and for tracking the progress of oil or gas recovery operations by detecting how fluids are moving through a reservoir.

MORE INFO Microhole Technology Initiative Produces One-of-a-Kind Expandable Wellbore Casing

For microdrilling to be accepted by industry, especially by independent, small service companies, a host of new equipment - from perforating equipment to logging tools to artificial lift pumps - will have to be developed at microhole sizes. The key will be to develop a full array of well service capabilities that can be miniaturized and deployed at significant cost savings. These are the challenges the Department of Energy has pursued.

MORE INFO Initial Market Evaluation Support [203KB PDF] Microhole Workshop Summary 01.31.05 Techline: DOE Announces 2005 Microhole Technology Projects

To assist in the planning process for DOE's Microhole Technology Initiative, a workshop was held in April 2003 with petroleum industry operators, service companies, and equipment suppliers, to provide input to the planning process and assist in developing a roadmap for the technology development.

In January 2005, the Office of Fossil Energy made awards for ten new microhole technology projects. The total cost of the projects is nearly $14.5 million, with DOE providing $7.7 million. The industry cost share of about 47 percent demonstrates the strong commitment to these advanced technologies and suggests high potential for their future commercialization and deployment. An earlier round of awards, announced in June 2004, involved six projects valued at nearly $5.2 million. This latest round in 2005 takes the evolution of microhole drilling a major step forward, with field demonstration projects being implemented in addition to technology development projects.

Microhole systems R&D supports broader DOE oil and natural gas program objectives to facilitate the development of ultra-low environmental impact oil and natural gas exploration and production methods.