Drilling advances

Vol. 232 No. 10

Geothermal fans say prospects are not just a lot of hot air

A few years ago, the service company where I was working tendered for a proposed multi-well geothermal drilling project in Hawaii. Needless to say, there was no shortage of wellsite engineers clamoring to be considered for the potential assignment, as well as one starry-eyed marketing communicator.

As the world continues its love affair with all things green, geothermal energy has reemerged as a darling of the alternative energy champions. And it would appear that predictions for an upswing in geothermal drilling are not, ahem, so much hot air. 

A Bloomberg article published in June suggests that investments in Indonesia’s geothermal sector alone could top $30 billion, with Chevron leading the way to tap the natural heat buried primarily underneath the rainforest. 

The US has long been a proponent, as evidenced by the 1976 creation of the Department of Energy’s Geothermal Technologies Program. Since the early 1980s, management responsibility for the DOE drilling technologies program has been under the auspices of Sandia National Laboratories (SNL). On May 27, 2009, the Obama administration earmarked $350 million in new investment to develop the technologies needed to spur wholesale geothermal deployment.

Two months later, the administration suffered a setback with the sudden shutdown of the much ballyhooed Geysers geothermal development in Sonoma, California. The final straw for the Geysers project was the closure of a similar project in Basel, Switzerland, which authorities had connected to a series of small earthquakes. Californians are justifiably jittery when it comes to earthquakes and, with the Geysers located smack-dab along the dreaded San Andreas fault, the feds had no choice but to pull the plug.

The DOE, however, remains undeterred in its devotion to geothermal, saying the Geysers, like Basel, required fracturing deep bedrock, which was blamed for the Swiss quakes. The federal agency contends that these locations were exceptional, and most geothermal wells do not require deep bedrock fracturing.

Chevron, likewise, is bullish on geothermal, especially considering that the actual well construction differs little from that of an ultra-high-pressure, high-temperature (HPHT) oil or gas prospect—albeit to the extreme, with bottomhole temperatures reaching well over 450°F. Stephen Green, Chevron’s vice president of policy, government and public affairs, told Bloomberg “There are synergies between oil and geothermal, and it makes sense for us to exploit that.”

Indeed, the same downhole problems that often plague HPHT oil and gas wells also extend to geothermal, though the severity is much more pronounced. Chief among the drilling problems are the unacceptably low rates of penetration (ROPs), as even new-generation drill bits find it rough going in the extremely hard and abrasive rock encountered in areas with a history of volcanic activity. Bloomberg reported that the 84 geothermal wells Chevron drilled in Indonesia each required up to 90 days and $7 million to drill an average depth of 10,560 ft. AltaRock, the erstwhile Geysers contractor, reportedly ran into problems at the onset, with repeated bit failures when drilling the shallow caprock.

Consequently, the costs of drilling a deep geothermal well, including very expensive titanium alloy casing (to resist the corrosive effects of geothermal fluids) and heat-resistant insulated drill pipe, can make even the most ardent enthusiast skittish. Little wonder, then, that improving hard-rock roller-cone and PDC bit technologies to improve ROP is at the top of SNL researchers’ to-do list, ahead of lost-circulation prevention and treatment, high-temperature downhole instrumentation and rig instruments for monitoring extreme operating conditions and identifying problems. SNL is working with Salt Lake City, Utah-based geomechanical analysis company TerraTek, which was acquired by Schlumberger in 2006, to develop and test a variety of high-temperature seals and lubricants for roller-cone bits, as well as unsealed steel-tooth bits for extending operational life in hot and abrasive environments. Researchers are also looking at rock-cutter interaction and frictional heating of cutters with an aim to advance the use of PDC bits in hard-rock geothermal drilling.

Lost circulation is another serious downhole problem for geothermal drillers. The DOE attributes 3.5% to 10% of the total costs of a geothermal project to lost circulation. Besides losing drilling fluid to the formation, lost circulation raises the risks of stuck pipe, damaged bits, slower ROPs and, at worst, collapsed wellbores.

The agency retained Texas Tech University to conduct a study of drilling fluids at high temperatures, with most of the emphasis placed on water-based muds, which are far less conducive to lost circulation than invert-emulsion systems. At the same time, SNL designed and built a test facility with an HPHT flow loop to examine lost-circulation materials capable of withstanding abnormally high bottomhole temperatures.

Another lingering issue that operators in the parched Eagle Ford can relate to is the availability of fresh water required primarily for geothermal cooling towers. In response, the DOE’s National Energy Technology Laboratory has embarked on a high-temperature nanofiltration program that would convert produced water for reuse in geothermal projects.

Clearly, economic and technological limitations must be overcome, but governmental and industry proponents remain convinced that geothermal energy is simply too abundant and too clean to be ignored. And, from all indications, they are not just blowing off steam.