Advanced Technonogy

Laser drilling in open spaces is a wonderful technology that can liquefy and penetrate rock quickly with no vibration. However, applications fall apart when spaces become confined, temperatures and pressures rise, and the material/fluids encountered create new problems. The hard minerals mining industry is closer to the use of laser drilling, largely because shallow applications do not require casing strings or encounter high external temperatures, high pressures, or hydrocarbons.

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Scientists estimate the 3,000 ft thick deposits of methane hydrate on the Blake Ridge off the US's central Atlantic coastline would provide gas for 20-30 years at recent US gas consumption rates. Shown is a core sample retrieved from the Blake Ridge by the Deepsea Drilling Project and research vessel Resolution. As layers of sediment are added to the seabed, the hydrate deposits are gradually pushed beneath and the bottom hydrate layers melt as they encounter higher internal temperatures. Along with the melt and new contributions of gas from below, the deposits have as much free gas as is bound up in the hydrates.


Many problems confront laser drilling

Laser drilling in open spaces is a wonderful technology that can liquefy and penetrate rock quickly with no vibration. However, applications fall apart when spaces become confined, temperatures and pressures rise, and the material/fluids encountered create new problems.

The hard minerals mining industry is closer to the use of laser drilling, largely because shallow applications do not require casing strings or encounter high external temperatures, high pressures, or hydrocarbons.

Lasers are optical systems, which eliminates the use of a circulating gas or liquid that could distort the beam between the optics and formation. A scrubbed gas could remove melted rock and expose new formation surface. However, what's to be done with the volume of re-solidifying rock material as it leaves the laser area? There are other challenges to be dealt with:

  • Excess heat: Heat is an immediate problem for the laser equipment as well as monitoring and steering tools behind the bit. Would cutting speed be great enough to distribute excess heat into the formation, or would it require a circulating air or fluid?
  • Gas emissions: Some elements and hydro carbons under heat emit large volumes of gas. How can these emissions be handled without creating an environ mental problem at the surface?
  • Inert gas: What types of oxygen-free gas can be used for circulation downhole and can the gas be scrubbed of emissions inexpensively and recirculated?
  • Drive system: Do you push the tool downhole with hard pipe or provide a local drive?
The rock volumes displaced, in a liquid state, could be pressure-squeezed into the formation, but highly consolidated formations could require lifting the re-solidifying material to the surface or to an injection point higher up. In theory, the re-solidifying material could be ground into a powder or sand behind the laser tool and lifted to the surface with fluids or gases that emerge behind the tool. The fluid would act also as a cooling agent.

There is another option for rock disposal - on-site casing formation. The rock melted by the laser could be deposited concentrically in a re-solidified state behind the drill bit. The melted materials would bond to the formation, eliminating both a casing run (at least temporarily) and cementing task. The casing-like skin would have to be monitored for thickness and density, and reinforced where needed.

In order to compensate for low volumes of liquefied material in unconsolidated formations, two options are possible: (1) A larger radius of rock could be liquefied in order to build a thick wall, but this might leave an objectionable void behind the wall. (2) A binder and extender of some type could be injected into the melted rock to compensate for the shortage.

There are benefits to the use of lasers that might compensate for the problems: (1) A 10,000-ft well could be drilled in a matter of hours. (2) Formation fluid inflow would be walled off and well control might be easier. (3) Laser tool monitoring and guidance would be handled through channels in a cable or coiled tubing system. (5) Vibration of the drilling equipment would be eliminated.

Because a re-solidified product would penetrate the formation and set up a substantial barrier to hydrocarbon flow, penetration of the producing formation would probably require pulling the laser unit and inserting a conventional mud motor and drill bit.

Where formations are in motion or formation pressures too high for a rock skin/casing, steel casing, which has unparalleled abrasion resistance and yield strength, could still be required.

A great many systems have been developed to support mechanical rotary drilling and steel casing. Both are formidable, and a reason why research has been slow to develop competitors.

Acoustics, EM waves even farther out

If laser drilling is still a long ways off in terms of improving downhole drilling, are acoustical and electromagnetic measures (microwave, radio frequency, or low frequency) any closer to reality? Manufacturers of conventional drilling equipment are probably safe for at least two more decades, unless US, Russian, and Israeli weapons laboratories choose to spin out some of their research.

Acoustics have the most appeal for drilling purposes, although microwave technologies may be the first to reach commercial introduction (more commercial research and less military secrecy). Acoustical waves directed at a formation face can reduce it to a powder, or an emulsion if liquids are present, very quickly. The powder can be blown free and lifted to the surface with air. A drilling fluid can be circulated to remove an emulsion. There is a concern over vapor volumes generated by the acoustics process when liquids are present.

Besides vapor generation, another major concern with acoustics is confining the wave to the target surface. The wave could collapse unconsolidated formations outside the wellbore area, leaving quite large radial voids.

However, this same capability might make acoustics a good technology with which to erode the skin in producing formations and enhance permeability and porosity some distance from the wellbore, especially if the acoustical wave can be directed.

Just as optical lasers, electromagnetic radiation (long and short wave) heats up the targeted surface and alters the molecular bonds. With sufficient power, microwave's impact on hard surfaces, like most other electromagnetic pulse waves, is to emulsify the material.

The costs of pure research, combined with the significant progress made in drill bit mechanics, deviated drilling, and lateral drilling technologies, have constrained most investigation into conventional drilling alternatives. Now that the costs of conventional drilling are rising, producers and drilling contractors may decide to renew the search.

Paraffin crystallization process developed

Two German chemical companies reportedly have developed a technology that will crystallize paraffins out of oil emulsions or reverse the process without solvent additions or temperature variations. The size of the conversion equipment and power requirements were not revealed by the developers, Sulzer Chemtech and Schumann Sasol of Hamburg.

Conventionally, paraffins drop out of oil flows as the wellbore or flowline temperature drops and deposits on colder surfaces. Producers have a choice of using insulation or heat tracing to maintain flow temperatures or introduce solvents where the temperature change becomes critical to keep the paraffins in emulsion.

Copyright 1997 Oil & Gas Journal. All Rights Reserved.

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