Pushing the Limits of Well Drilling
The past 100 or so years have seen some revolutionary changes in the drilling industry. One thing we have not done is stand still. Our ability to explore, and exploit, ever more difficult horizons has kept pace partly because of the money involved (there’s a lot …) but mostly because brilliant minds take up the challenge. The drilling industry is different than any other industry in one regard. Of course there are plenty of very well educated engineers, but it is one place where a man’s ideas come before the diploma hanging on the wall. In the history of our industry, you will find most of the good ideas came from a hand, sitting on a bucket, solving a problem. He may not have much formal education, but he probably has spent a lot of time on “the sharp end of the stick.” Bosses and investors soon learned to listen because, if they didn’t, the company right down the road would.
Some of the more interesting developments have come in geothermal drilling and power production. I’m not talking about geo-loop systems, which use the earth as a heat sink, but the tapping of the internal heat of the earth. They are pretty well scattered out, but where available, hot rocks are a nearly inexhaustible supply of energy, provided we can produce it. For instance, Iceland generates most of its power from geothermal energy.
One of the most common production problems for the driller is, of course, heat. Above a certain temperature, metallurgy changes and pipe does strange things. Like get weaker. We have continuously improved the quality of our drill pipe to combat this heat, but it is still a never-ending battle. Another limiting factor, besides steel, is downhole tools. The electronics used in downhole navigation tools and wireline logging tools are notoriously fickle in perfect conditions, and a nightmare in hot holes. The big companies like Schlumberger, Halliburton, Baker Hughes and others have huge labs that work on this continuously.
Some years ago I got involved, as a consultant, on a project south of Angleton, Texas. It was discovered that the crust of the earth was thinner there than most any other place on the Gulf Coast, so an exploration hole was drilled. I asked how deep we were going to go, and the answer was, “As deep as you can.” Turned out to be between 13,000 and 14,000 feet. Bottom hole temperatures were high enough to weaken the drill string (we fished twist-offs several times) and ruin every logging tool we ran in the hole. The completed well made saturated brine that flowed to the surface with a shut-in pressure of about 2000 psi and hundreds of gallons a minute. Flowing surface temperature was almost 300 degrees. This was interesting because saturated brine at that temperature holds a lot more salt than brine at room temperature. This means that when we turned it loose through a flare stack, the water instantly turned to steam and it actually snowed pure salt. We built quite a pile during testing.
Texas A&M University was involved in the project from the beginning and they were quite excited about the amount of potential energy we were producing. They had visions of running a turbine and making all sorts of power. Good idea, right? Except that the brine was so corrosive that it destroyed parts within hours. They decided to use a giant heat exchanger to extract the heat without damaging the turbine. The way it worked was, they would build a heat exchanger on a huge trailer, bring it to the location and watch it self-destruct in a few days. Repeat procedure. We were used to that, so we would shut in the well and wait on them to come up with another idea. During waiting periods, I went off and did several other projects as I waited.
One of the things we didn’t take into account during our shut-in periods was the thermal expansion and contraction on the tubing string. We used very high grade 5-inch integral joint tubing that was just about as strong as anything I’ve ever seen. When we first started producing the well, the tubing heated up and, of course, got longer. This was no problem on the rig floor; we just picked up the block and took up the slack. It “grew” by about 12 feet. The problem occurred when we decided to shut the well in and put the rig on standby for a few days while the Aggies came up with another heat exchanger. The pipe was hot, and expanded to full length, and the crew set the slips for the shutdown. As the pipe cooled down, it contracted, except that it was anchored at the bottom by a packer and at the top by the slips. Did I mention that it was VERY strong pipe? By the time we got back, a week or so later, the tubing string had cooled, and contracted, and pulled the rotary beams down about 3 feet, resting on the top of the blowout preventer stack. The floor was a mess. In order to release the pressure on the slips, it was decided to pick up the string with the block. I wasn’t on the floor when it happened, but however much they pulled, they pulled the crown in on the rig!
They eventually put a new derrick on the rig and we got back in operation. One of the good ideas we came up with was a sliding sleeve in the tubing string to allow the string to expand and contract without cratering the rig. We worked, off and on, on that well for over a year until everybody agreed that, while that was a good idea, it just didn’t work … or was not economical. As we develop better ideas, it will be.
For more Wayne Nash columns, visit www.nationaldriller.com/wayne.