Laser-like precision

Jerry Lee and Greg App examine how lasers could be used for not just drilling, but for completions and well intervention projects, too.

Laser drilled sandstone core sample.  Images from ZerLux Hungary Ltd.

The oil and gas sector is constantly seeking innovations to improve economic efficiency, particularly to decrease the high costs associated with drill bits and non-productive time (NPT). This need for continuous improvement helped spark the first phase of the Gas Research Institute (GRI) funded research program aimed at utilizing high-powered lasers for drilling. Following the release of previously classified information from the US Defense Department’s Star Wars Laser technology in the mid-1990s, some in the oil and gas industry have developed an interest in harnessing the potential of laser drilling.

The primary advantage of utilizing lasers lies in cost efficiency. In traditional drilling operations, progress is often halted by the replacement of worn-out bits, stuck pipe and other inevitable malfunctions. Halting operations results in lost time and money. Another key method of reducing expenditure is the reduction of rig rental time. NPT is significantly reduced by removing the vast array of mechanical components associated with traditional drilling operations, the time associated with tripping in and out and replacing or repairing components. Efficiency is realized due to the continuity of the laser drilling operation. Once the operation begins, there is no bit to replace, and thus less cause to trip in and out. A laser drill can remain operational as long as there is an available power source.

Engineers work on perforation tool.

Further progress toward commercializing laser technology was spurred by the automotive industry. This investment resulted in the cost of 1W of laser drilling power dropping from US$1000/W to less than $50/W. Another major obstacle cleared was to prove that laser drills are not limited by the type of lithology.

There were also problems with the use of fiber optic cables due to Stimulated Brillouin Scattering (SBS). “[SBS] chokes off the transmission of high power laser photons in a fiber optic cable by reflecting the energy backwards to catastrophically destroy both the fiber optic cable and laser source,” says Foro Energy. However, with the introduction of SBS resistant fiber optics, the issue has been resolved. Additionally, current laser drilling developments have seen power availability increase from 1kW to 1000kW, as well as improvements in unit mobility and durability.

Yet, despite these advances, government funding for laser drilling research at institutions such as Argonne National Laboratory (ANL) has been cut. In response to this lack of government support, various private organizations have built upon the progress already made. For example, Foro Energy, the company responsible for the development of the SBS fiber optics, was formed by members of the original laser drilling research partnership between the Colorado School of the Mines and ANL.

Initially, two methodologies were considered for the laser drilling drive mechanism: rock melting or the spallation of the grains. Spallation occurs when laser-induced thermal stresses are applied to the grain causing it to fracture; however, the amount of energy applied by the laser must be low enough to keep the local temperature below the melting temperature. Depending on irradiance, or power per unit area, the laser rock interaction can cause the grains to melt or spallate.

“The most efficient way to laser drill through sandstone is spallation, where laser energy is used to break the bonds holding the grains together, creating loose sand particles,” says Neal Skinner, senior scientific advisor at Halliburton. The grains are then removed to expose the next layer of rock.

“Shales also spall in a manner similar to sandstone. Limestone, however, is mainly calcium carbonate and undergoes a different process for laser removal,” he explains, adding that under temperature, limestone dissociates into calcium oxide and carbon dioxide [CaCO3 -> CaO + CO2]. “Calcium oxide is a white powder and easily purged from the hole with gas or liquid.”

The Core Laser Team.

Contemporary application

The technology and the benefits surrounding laser drilling are enticing. However, economics are usually the governing factor when making decisions in the oil and gas industry. Currently, implementing laser drilling technology is not as cost effective as conventional drilling.

Fiber optics at work.

“The issue is economics,” says Dr. Peter Bajcsi, COO at ZerLux. “It simply makes no business sense to deploy lasers to drill big vertical boreholes. Conventional drilling is still more economical to drill long laterals because the technology already exists. Conventionally drilled laterals improve the productivity of the wells and even connect two pay zones, so that’s not what we’re after.”

With the associated equipment, supplies, and services being readily available, drill jobs can be undertaken less expensively by conventional methods. The industrial logistics necessary for industry-wide laser drilling applications do not yet exist. Due to this limitation, the current focus of laser technology is on well completions.

“Laser perforating has its own value proposition and is easier than laser drilling. A certain irradiance or optical power per unit area must be delivered at the rock face to make things work. With a smaller hole, there is less area so less laser power needs to be delivered downhole,” Halliburton’s Skinner says.

The use of laser systems in completions operations is feasible because such systems can be incorporated with existing equipment. “The tool will be mounted on coiled tubing, which will sit on top of a specially customized bottomhole-assembly,” Bajcsi explains. “The idea is that we deploy the high-power laser source from the surface and transfer the laser light through optical cables to the laser head, which is going to drill into the formation reaching into the pay zones,” The laser generator on the surface provides a steady stream of energy through the fiber optic cable transferring 60-100kW of energy, equivalent to more than 1000 streetlights.

The focused beam melts the grains and creates molten rock, which covers the borehole with a glassy layer of obsidian, fusing the borehole and increasing borehole stability. This naturally impermeable glassy layer is made permeable by ZerLux’s proprietary methodology resulting in improved communication between the reservoir and the wellbore, as well as resisting sand incursion. The specially designed laser head then flushes out the debris, which is composed of thin, brittle fiberglass. The completions operation is done underbalanced, utilizing water and nitrogen instead of drilling mud.

Hard scale removal test.

Advantages of laser completions

Perforation techniques used to complete conventional wells often cause extensive formation damage. However, laser perforation causes no formation damage, and will extend past the formation damage caused by the drilling process, thus resulting in good pay zone-well communication.

“It is believed that the high temperature gradients generated in nearby rock creates stress, which causes microscopic fissures or cracks to form, increasing permeability,” Skinner says. Due to the positive correlation between payzone-well communication and production output, overall production is improved. Additionally, laser perforation results in lower water coning, reduced sand incursion, and more precision and control than conventional perforation. Hydraulic fracturing can similarly benefit from the utilization of laser technology by creating small starting holes for the fracturing process.

“Small-scale rock-mechanics laboratory tests suggest that if it were possible to make a 1-2ft-long perforation perpendicular to the wellbore, it would allow a bypass from the [damaged zone] to create more linear, less tortuous fractures,” he says.

Though industry has seen maximum perforation depths of around 4ft, ZerLux is building a tool that could penetrate the reservoir to 10-20ft deep while maintaining a larger diameter than that created by a perforation gun. However, its limits are dependent on the length of the bottomhole assembly. Additionally, the system’s electronics are susceptible to heat damage when external temperatures rise above 200°C.

Panel design.

Offshore applications

Laser technology is not confined solely to perforations or drilling applications. It also has potential as a well intervention tool. The mediation of barium sulfate hardscale accumulation in offshore wells is often challenging due to its resilience to most conventional well intervention techniques.

“Laser light will change the physical and chemical properties of the scale and that will allow very fast removal,” Bajcsi says. “No other technology can do that. Conventional milling just won’t work.” The accumulation of hydrates in flowlines and other subsea components is another common problem affecting offshore operations. Hydrate formation reduces production rates and can completely plug a piece of equipment. To address this issue, ZerLux developed two technologies — Blue Tube and Intra-Snake — to facilitate hydrate mediation.

The tools use a conventional remotely operated vehicle to scan equipment and selectively heat the affected area with its laser to treat the blockage without physical contact. This capability also allows hydrate plugs of varying length to be addressed, not just small plugs.

“These two technologies will allow operators to remove hydrates without entering the pipe. It is safer and much more economical than electric blankets and other conventional methods,” Bajcsi says.

Although lasers cannot economically address all the technology challenges, laser technology has the potential to improve efficiency in the oil and gas industry, as well as open up new opportunities.