With the recent housing downturn, a lot of drillers are expanding their horizons and looking for work different than what grandpa did. Geothermal drilling is one example. Actually, the better name would be geo-exchange drilling. Geothermal drilling usually is in search of hot rocks, and steam usually is produced to operate power plants. This heat-of-the-earth actually is available anywhere; it’s just not available at shallow-enough depths to make it economical. There only are a few places on earth where hot-rock drilling is commonly done, the most famous being Iceland. The most productive geothermal horizons in the United States are located in Nevada. New Zealand also has a well-developed geothermal industry, which produces a large percentage of its power.
But I digress; that is a subject for another article.
The principles of geo-exchange are deceptively simple, but a little more
interesting to execute. The first thing to remember: The only time you are
making any money is when the bit is on bottom, drilling. It is different than
normal water well drilling in that there is no development time, pump-setting,
or a lot of the steps we are used to. Your time needs to be adjusted with an
eye toward “critical path” drilling, about which I’ve written before. The
ancillary parts of the job, such as running the loops, grouting, testing and
the like, need to be done while drilling. In other words, when you get one hole
drilled, you move the rig to the next hole and get a bit on bottom while you
run the loop and grout. This probably will take an extra man on location, but
will pay for itself in productivity.
Another key to productivity is bit selection. We all have been guilty of
running bits that will make one more hole. Geothermal drilling is not the place
for these bits. Depending on the size of the job, it is a good idea to have
several new bits on location, not back at the shop. When a bit slows down,
change it out, and run a fresh one. You always can run those bits later on in a
well that does not have the time pressure. I know drillers who run Mil-Claw
bits that change the teeth on every hole, and it pays off.
If you are mud drilling on these projects, keep in mind that you are going to
use a lot of water, and make a lot of mud that must be disposed of. An on-site
water supply is a blessing, and fortunately they usually are available, but mud
disposal should be carefully considered before you get yourself knee-deep. If
you are lucky, there is a convenient pump-off area within a reasonable
distance. If not, you are going to have to haul it off. This is another task
that doesn’t need to interfere with the bit-on-bottom time.
A much faster and more productive way to go when drilling with mud is to have a
commercial mud system on location. These usually can be rigged up in a central
location between holes, saving a lot of time mixing new mud for each hole.
Also, most of the better units put out fairly dry cuttings that can be hauled
offsite easily at the end of the day.
These are a few of the critical-path procedures I’ve used over the years that
have helped me stay competitive on geothermal drilling jobs; I hope they
As I write this, I’m sitting in my room at the national convention in Las
Vegas. I was invited to go out for a steak tonight by a good friend, and the
second-best driller I know, from Nephi, Utah, named Charlie Eppler. The
schedule has now changed. Last night at 3 a.m., Charlie’s pacemaker quit, and
he had to be hauled to the hospital. We all pray for his speedy recovery. When
I see him next, I’m going to tell him if he didn’t want to buy supper, all he
had to do was say so ....
The World According To Wayne: Geothermal Drilling
January 1, 2009