A journey to the centre of the earth

In 1864, Jules Verne imagined a trip to the centre of the earth through an old volcano using rope. Descending 21 miles down, the three protagonists discovered an underground ocean, mushroom forests, dinosaurs and even a 12-foot tall prehistoric man. Unfortunately, as anyone who has ever been involved in deep drilling knows, this was science fiction.

The realities of deep drilling are high pressures and high temperatures; a hostile environment that means tapping into deep reserves is dangerous and expensive.
With temperatures greater than 400oF and pressures above 15,000psi, when drilling nearly three miles down it is not unusual for the drill bit to slow to as little as two feet per hour. And it is incredibly difficult to control the direction of drilling.

When you’re paying thousands (or even millions for off-shore rigs) of dollars a day it is not hard to see how costs can ramp up. On wells deeper than 15,000 feet, the Department of Energy (DOE) estimates the average cost per foot is more than double that of shallower wells, with as much of 50 percent of the drilling costs spent on the last 10 percent of penetration.

It is no surprise then that wells below 15,000ft account for just seven percent of the gas produced in the US. And yet the potential of deep drilling is huge. Many of the basins that produce the nation’s natural gas contain sedimentary columns that descend to 30,000ft or more, and this potential deep gas resource is enormous. There is an estimated 125 trillion cubic feet of natural gas thought to be trapped at deeper depths – that’s about 29 percent of the nation’s total reserves, and equivalent to about five year’s worth of the US’s total gas consumption.

Digging deeper

Because of the eye-watering costs involved, it has so far only been economic to develop the most promising deep prospects. Drilling at such depth tests available technology to the limit, which in no small part adds to the cost. But because of the small amount of deep wells sunk (only around one percent of total US wells penetrate below 15,000ft) it is harder to invest and develop new technologies, which would bring the cost of drilling down.

Basic economics suggests that eventually, when the shallower gas runs out and supply begins to wane, continuing demand will force investment and more deep drilling will happen. The only problem with the theory, of course, is that left to the market there could well be a technology lag that in the short-term interrupts supply – not a great scenario.

In order to avoid this possibility and kick-start the investment cycle, in 2002 the DOE set up the Deep Trek program. Run through the National Energy Technology Laboratory (NETL), the program aims to advance the understanding of deep gas environments and develop new technologies to reduce deep drilling costs and increase drilling efficiency.

Deep Trek

The program is a collaborative program that invites private contractors to propose technologies that will operate at extreme temperatures and pressures (more than 347oF and greater than 10,000psi). Applications that NETL believes have merit are awarded funding grants and a three-phase development is undertaken. Phase I is a feasibility and concept definition stage, phase II consists of research and development of prototypes, while the final phase III is a field development and commercialization.

The goal of all Deep Trek projects is to produce commercial drilling products that will be available to drilling companies nationally. To date, the DOE has awarded 12 Deep Trek projects, with funding of US$31 million and research partners contributing a further US$12 million. In addition, it is also managing another seven projects that are focusing on resource assessment and improved imaging technology for deep reservoirs.

The program builds on the earlier success of DOE funded research. For example, the polycrystalline diamond drill bit, which is now the industry standard for drilling into difficult formations, is based on a ‘diffusion bonding’ approach that was first developed by scientists at the DOE’s Sandia National Laboratory.

Super cement

By their nature the Deep Trek projects are long-running investments, but successes have already begun to come out of the program. In January this year, the DOE announced that a ‘super cement’, developed by CSI Technologies LLC (formerly Cementing Solutions, Inc) with Deep Trek funding, has been commercially applied by several companies to seal leaks during drilling at depths of up to 10,000ft.

Cement is used in drilling between the casing and wellbore, and needs to be able to withstand changes in pressure in high temperature environments. The cement also needs to remain sound over the productive life of the well, often up to 30 years. The standard practice is to use Portland cement. However, as you increase temperature and pressure, this cement has inherent weaknesses that make it unsuitable for use in deep wells. Repairing failed cement jobs in deep, hot wells has been estimated to cost the industry more than US$50million each year.

To address this problem CSI developed its super cement, known by the brand name ULTRA SEAL-R(Liquid Bridge Plug), with superior pipe- and formation-bonding capabilities. CSI analyzed various cement materials in the lab to identify the optimum mechanical properties for withstanding extremes of pressure and temperature, and developed a sealant resin to mimic the optimum properties.

Following a successful field-scale test on the sealant, CSI offered the sealant to a major offshore operator that was having difficulties in sealing some its wells with Portland cement – the ULTRA SEAL-R successfully did the job. The same operator then applied the seal to a leaking packer set at 10,599ft inside a seven-inch casing. The ‘super cement’ sealed the leak at a temperature of over 200oF.

Following these successful applications, other operators are now scheduling use of the seal, and CSI is expecting to test different formulas in deep wells through this year. It is anticipated that any additional cost of these new formulas will be off set by long-term savings in maintenance and repair costs, associated with the enhanced integrity of the seal. Given that the industry currently spends so much on repairing leaks, the US$2.5million cost-shared Deep Trek contract that funded this project looks like good value.

Smart drilling

CSI’s super cement is just one small part of the Deep Trek program’s goals. The cornerstone of the project is to develop a suite of high-temperature electronic components that can be used for instrumentation in deep gas drilling systems.

To develop this, DOE partnered with Honeywell International and invested US$6.7million dollars to develop heat resistant components. Using silicon on insulator (SOI) technology, Honeywell has successfully developed and tested four critical high-temperature electronic components capable of operating at temperatures up to 437oF for at least five years.

While its work in the area is ongoing, it has reached the following milestones:

• Developing an electrically erasable, programmable read-only memory (EEPROM) chip. It has developed two test chips that prove this technology, and the EEPROM is currently undergoing a full-scale field test.
• Successfully testing and developing a precision amplifier (OpAmp), which conditions data signals received from downhole sensors.
• Achieving a first-pass success test of a field-programmable gate array (FPGA), which is a semiconductor device that features programmable logic. These flexible chips can be reprogrammed in the field to accommodate a change in purpose.
• Designing an 18-bit analog-to-digital converter (ADC), which basically converts voltage to a binary digital number. The goal is to develop an ADC with a 16-fold improvement in resolution on the existing standard.

The successes that Honeywell has been having in developing these components can be seen by its success in attracting more Deep Trek funding. This summer the DOE announced that it was to make another US$773,000 funding available to extend the SOI technology and develop a reconfigurable processor for data acquisition (RPDA). The RPDA would combine SOI circuitry with the FPGA and a non-volatile memory chip in a rugged ceramic package. The whole module will be tailored to the physical constraints of downhole measurement-while-drilling.

Ongoing projects

These two successes of the Deep Trek program are hopefully just the start of several technological breakthroughs that the program will develop. There are many other projects that will hopefully materialize into more substantive outcomes in due course. For example, APS Technology Inc has been developing a two-component system to monitor and control drilling vibrations. The first component based on a unique, multi-axis active vibration damper to minimize harmful vibrations. The hydraulic impedance of this damper will be continuously adjusted and monitored by the second component, a real-time system that is also under development. This will help increase drilling efficiency by keeping the bit in contact with the cutting surface for longer, while increasing bit life by reducing shock and vibration damage.

Meanwhile, GE has just received funding to develop a flexible, polymide-based package for housing electrical components. The packaging is needed to protect new electronic components not just from the temperature at depth, but the vibrations from drilling. GE is testing three different strategies to interconnect the electronics: gold stud bumping, high-temperature solder materials, and plated-copper microvias in the polymide.

On a different note, Drill Cool Systems Inc in California is trying to extend insulated drill pipe (IDP) technology that has been used in geothermal drilling to a deep drilling environment. IDP delivers fluid to the bottom of a wellbore at much lower temperature than a conventional drill pipe, which should protect downhole equipment that is vulnerable to high temperatures.

Scratching the surface

While there is still much work to be done on all these projects, it is work that needs to proceed now. Given both the insecure global energy environment and the dwindling shallow reserves of gas in the US, it’s clear that in the future we’re going to have to be more effective at drilling deeper. It’s unlikely we’ll fine the 12ft humans and mushroom forests that Jules Verne imagined, but as we journey closer to the center of the earth, what lies at these greater depths could be just as exciting for oil and gas explorers.