Stripper Wells: Fire in the Hole!

Byron King recounts watching an oil well being blasted, then discusses what Stripper Wells are and how important they are to America.

Our host turned around and faced the other direction, again yelling, “Fire in the hole!” His voice trailed off into the endless vista of oak and maple and black cherry tree trunks, mostly barren of leaves by the middle of this chilly, but very sunny and bright November day. Then, our host smiled (we were all smiling) and stepped over to the blasting machine that was sitting on some 6-by-6-inch pieces of lumber at the edge of a corrugated steel lean-to.

“Everybody get ready to move under cover in case any fly-rock comes out,” said the blaster, Richard Tallini, a licensed explosives expert who has been setting off high-energy charges since 1967. That is, if any rock or other debris came shooting up and out of that hole, we were all supposed to dive for cover under the corrugated steel structure. I’ve dropped a few 500-pound bombs in my life, back in my days flying jet bombers in the U.S. Navy. So our host did not have to tell me twice about respecting the outcome of a major explosion.

In the second-to-last step of a long sequence of events, all performed with the utmost attention to detail and safety, our host pushed the yellow button that closed the electric priming circuit. We could hear the increasing sound of the capacitors — not unlike the whine of a distant jet engine — as they were charging.

By virtue of winning a coin toss with his 9-year-old sister, a young fellow named Max King, all of 6 years old, had the honor of pushing the red detonator button. In less than the blink of an eye, the capacitors discharged and sent a pulse of current through a yellow wire. The charge moved at the speed of electricity in copper, across 100 feet of Venango County hillside, and down more than 900 feet of wire to an 8-foot-long tube at the bottom of a hole.

Stripper Wells: Rocket Fuel in an Oil Well

Inside that tube, at the bottom of the hole, was about 75 pounds of high-energy propellant (not explosive, mind you), a rubbery compound not unlike the material that powers the solid rocket boosters on the U.S. space shuttle. Rocket fuel? In an oil well? Yes. It beats the heck out of nitroglycerin, the stuff they used to use for this down-hole purpose.

You can hit this rocket fuel with a sledgehammer and it will not blow up. But turn a 6-year-old loose on it, and watch out. Max’s well-timed electrical pulse moved down into the earth and triggered a priming charge at the top of the tube, which caused an explosion that accelerated down a detonation pathway inside the package and thus ignited the propellant. Kaboom!

We were close to the action, but we were also far away. It was as if we were standing on the observation deck of the Empire State Building and the explosion had occurred at street level. It was a long way to begin with, at least vertically. And it all happened in the very tight, narrow confines of an oil well.

If you are not familiar with the processes of things subterranean, it would seem that strange events must occur down at the bottom of a hole in the ground. Even if you are familiar with the technical geological processes, it is truly the case that strange and mysterious things happen down there all the time.

Miners and drillers and blasters even have their own protective patron saint, the good and beatific St. Barbara, to ward off the odd and sometimes evil things that occur at depth. After all, when the world literally comes crashing down upon your head, what must be your last thoughts? There are no atheists in foxholes, they say. Nor at the bottom of dark pits and shafts and wells, let me add. But that is another story for another time.

The first several hundred feet of this particular oil well, from the surface to down below the glacial till and weathered zone of the bedrock, are lined with steel casing. This steel casing serves to stabilize the hole and to protect the ground water from contamination by salt and brine waters from the depths, or by leaking oil that forms part and parcel of those down-hole fluids.

Stripper Wells: Open Hole

The remainder of the well, down to total depth, is what is called “open hole,” penetrating through just plain, solid, 380-million-year-old Devonian rock of the continental crust that forms the western foreland of the Appalachian Mountains. This hole in the ground penetrates numerous thin, oil-bearing sands on the way down. And it comes to an end after making its way well into the famous “Venango second sand” of this historic oil-producing region.

The 8-foot-long charge, lowered on a wire to a precise depth near the bottom of the hole, was underneath about 100 feet of water column. The water came into the hole courtesy of the natural seepage from the sides of the well, into the open bore beneath the steel casing. This water column also served to contain much of the energy from the propellant at the bottom of the well bore, instead of allowing the energy to explode upward, like what happens when a bullet is fired from a long gun barrel. Ideally, you want to keep your energy down in the hole, where it can do you some good.

The idea is to channel that rocket fuel energy, via hydraulic shock, for as long as possible (milliseconds, really, but that is the physics of shock waves) against as much as possible of the oil-bearing sandstone. At depth in the well, the hydraulic shock wave travels at ultra-high speed (much over 10,000 feet per second) through the mixture of oil and water that permeates the rock, and also channels through the fractures in the rock. Most of the transmitted energy is mechanical, in the form of the shock wave front. The wave front pushes through the fractures and opens and expands new fractures.

Some of the energy that you release is also transformed by heating the down-hole fluids, leading to vapor expansion opening up the fracture systems via the effects of superheated steam. The bottom line is that you want to maximize the one-time pulse of the energy release and place that pulse against the maximum amount of surface area. Get it? There is, of course, a method to this madness.

Many years ago, when this particular oil well was first drilled by the Quaker State Oil Co., the geologists and engineers took the time and went to the expense of fracturing the oil-bearing sands with a high-pressure water charge. It is called, in the industry, “hydro-frac’ing.” That is shorthand for “hydrological fracturing.”

To make a long story short, hydro-frac’ing involves getting a couple of big pumper trucks out on the well site and pressurizing water down your hole in the ground. The pressurized water works its way into the natural zones of weakness that are present in every sedimentary rock, particularly those of the second sand in these Devonian formations. In the case of this particular well, the idea was to fracture the oil-bearing sands with high water pressure early in the life of the well, and thus increase the surface area of sand that could drain oil into the well bore. It was and is a well-known technique to increase the short-term recovery of the Pennsylvania-grade crude oil contained within.

Yes, indeed, it worked. This particular oil well was a good producer for Quaker State for many years. The oil was consistently able to seep out of the exposed rock surfaces that were fractured at depth. The oil then migrated, both by gravity and through the hydraulic assistance of natural water flow, along the fractures (mostly microscopic cracks, really) and into the well bore. Once in the well bore, the oil could be pumped to the surface and collected via a system of gathering pipelines.

But eventually, the oil production from this particular well, and from its neighboring wells, declined to a point where Quaker State sold everything off. Quaker State could not be bothered with wells that were producing only a few barrels of oil per day, let alone a few barrels of oil per month. So other operators purchased the lease rights to the oil field containing this well, and all of the nearby wells.

This well, the one we were “shooting,” and many others similar to it, passed to operators who were and are willing to invest the time and labor (and it takes a lot of labor, I assure you) to coax whatever oil is left into the well bores. The well shot that we witnessed was an attempt to put new energy down and through the old fracture systems, and thereby enhance the oil production.

Stripper Wells: What a Stripper Well Is

Let us digress for a moment. These low-volume well operators are, in effect, “stripping” the remaining oil from these holes in the ground. And these oil wells are called, appropriately enough, “strippers.” It works kind of the same way for gas wells, too.

But without the aggregate production of these stripper wells, the United States would have to import an additional 900,000 barrels of oil a day, an increase of almost 10% over current imports. And without natural gas from U.S. stripper wells, the United States would be required to import an additional 1.5 trillion cubic feet of natural gas per day, an increase of about 38%. Thus, cumulatively, oil and gas stripping is a keystone of U.S. energy supply.

There has been quite a bit of progress in recent years on life extension technologies to reduce the need to plug and abandon stripper wells. In 2002, for example, more than 3,800 gas wells and 14,000 oil wells were plugged and abandoned nationwide, even though most of the wells were still producing hydrocarbon fluids, albeit at very low rates. The long-term implication is that once stripper wells are plugged and abandoned, the costs to re-enter the formerly producing oil or gas strata (typically by drilling a new well) are prohibitive. The energy resources may as well be lost forever.

Both government and private industry are continuously working on ways to extend the lives of these stripper wells. There is a group called the Stripper Well Consortium, an industry-directed effort whose research, development, and demonstration efforts are co-funded by the DOE, through the National Energy Technology Laboratory’s Strategic Center for Natural Gas and Oil. This group has come up with some very good, innovative ideas. But not all progress comes from the government-funded gods of Mount Olympus.

Sometimes, progress comes from the likes of a small company with an old facility near Titusville, Pa. Which gets us back to our weekend well shot. Our host was one of the owners of the Otto Cupler Torpedo Co., a privately held firm that traces its history back to the very beginnings of the well shooting industry in the 1860s. (Originally, Otto Cupler was called the Roberts Petroleum Torpedo Co., named after Union Army Col. E.A. Roberts who first patented the “well shooting” concept. This is the basis for another Whiskey article for another time, dear readers.)

Stripper Wells: A New Kind of Well

What we were witnessing the other day in the woods south of Titusville was a new kind of well shot that is a vast improvement over the old and dangerous manner of stimulating a well by exploding liquid nitroglycerin. It also is an improvement over using other, but safer, forms of high explosives. Nitroglycerin and other high explosives tend to shatter the rock, and in many instances cause the well to plug up with large amounts of debris, instead of increasing production.

But by utilizing modified rocket propellant, the down-hole energy and velocity characteristics are quite different from those of high explosives. That is, there are fewer tendencies to shatter the rock formation, and an increased likelihood of expanding an existing fracture system, thus increasing the surface area from which the oil can drain from the oil-bearing strata and into the well.

As the world reaches and passes the point of Peak Oil, and as more and more of the world’s oil wells and oil fields go into irreversible decline, the stripper segment of the industry will play a more and more important role. There will, of course, be new techniques developed to locate and recover those last precious barrels of oil from the rocks underground. Some of those techniques will probably be so innovative and unusual that their roots will date back to the 1860s and the founding of the petroleum industry. But then again, didn’t some famous book once note that there is nothing new under the sun?

So as I bid you farewell, allow me just to remind you of something important. When you are out in the woods and you hear someone holler, “Fire in the hole!” you had better duck.

Until we meet again,
Byron W. King
November 18, 2005