High Energy Gas Fracturing (HEGF) is a common generic name used by the oil and gas industry for the technology of stimulating wells with propellant gas generators. Other names which have been used for this technology include Tailored Gas Pulse Loading, Tailored Gas Pulse Fracturing, Controlled Pulse Pressurization, and Controlled Pulse Fracturing. Modern propellant type well stimulation devices were developed around 40 years ago. Since that time, dozens of patents have been issued for different flavors of gun propellant / rocket fuel / low explosive well stimulation schemes; we have a stack around a foot tall. One variant of the technology involves propellant assisted perforating, where a perforating carrier and a propellant stimulation mechanism are merged into a single hybrid system (contrary to the StimGunTM hype, this is not a new idea as patents for hybrid devices go back decades).The Players
The proponents of propellant stimulation correctly state that high explosives, such as nitroglycerine, detonate and create a shockwave and high pressures that last only a few microseconds. They believe a slower reaction time is crucial to success. They cite research that demonstrates high explosives enlarge the wellbore by crushing and compacting rock, resulting in a zone of residual compressive stress. They argue that this zone, sometimes referred to as a stress cage, can actually cause a reduction in permeability in the near wellbore region. Perhaps this explains why some high explosive well shots fail to improve, or even seem to hurt production. But, the proponents fail to adequately address why historically many high explosive shots have been wildly successful. Keeping things in perspective, it should be noted that the
first successful well shot in 1865 was actually a propellant shot using eight pounds of black powder (two years before the first use of nitroglycerine).
The propellants used in these devices do not detonate supersonically, they deflagrate at subsonic velocities. Deflagration can be simply explained as a rapid burning process that takes place without an outside source of oxygen. Propellants have energy densities approximating those of high explosives, and are thus more compact than any other prime energy source other than nuclear. The propellant type devices typically produce a high pressure event lasting on the order of a few milliseconds to perhaps a few hundred milliseconds, as opposed to a few microseconds for high explosive well shots. It is argued that this longer event time is the secret to producing multiple fractures and avoiding stress cage damage (some research suggests that if the event time is too long, only one or two fractures will be produced as with hydraulic fracturing). The event time difference probably does explain why propellant stimulations require typically little or no cleanout as opposed to lengthy cleanouts after many high explosive shots.
This technology has been inadequately investigated, yet some of the companies offering propellant stimulation devices claim to be able to fine tune their product to fit specific well or rock conditions. They may somewhat understand the behavior of their various propellant recipes at different depths, and they may even have good reason to use different recipes for cased hole or open hole completions, but beyond this very basic tailoring, these claims should be viewed with skepticism.
Thousands of HEGF well stimulations have been conducted over the course of the last few years (thanks almost entirely to the efforts of Dr. Schmidt at The GasGun, LLC), and thus propellant well stimulation is taking on the character of a commodity service much like Liquid Nitroglycerine (LNG) high explosive shooting was for many decades. LNG shots remained popular for shallow wells particularly in the Illinois and Appalachian Basins for many years after hydraulic fracturing displaced the practice for deeper wells. Hydraulic fracturing is notoriously ineffective in very shallow wells where principal stress factors favor the formation of undesirable horizontal fractures. These shallow wells may be especially good candidates for HEGF stimulation now that LNG is no longer available.
Servo-Dynamics, Inc. claims to be the originator of propellant technology, and Henry Mohaupt, the president of the company, does in fact hold some of the earlier patents on propellant well stimulation. They call their version of the technology the STRESSFRAC®. At present, their approach to sales and service is impractical with respect to shallow stripper wells.|
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The GasGun, LLC offers the GasGun®, which technology was developed and refined with a DOE grant. Much of the proponent explanation above was borrowed from the writings of Dr. Schmidt; he and his son run the company and they are very nice folks. The company has entered into agreements with logging companies to field the GasGun®, which device is the most reasonably priced product listed on this page. Thousands of GasGun® stimulations have been conducted, often with very good results. Also see SPE/DOE 8934 which is a detailed technical paper written about tailored-pulse well shooting studies conducted by Sandia National Laboratories.
Owen Oil Tools, Inc. manufactures a hybrid device called the StimGunTM. But abandon all hope of using this nifty technology if you are an independent logger; the licensing fee was in the neighborhood of $260,000.00 (when reliable information was last available) thanks to Marathon and the development consortium.
GEOTEC (Geotec Thermal Generators, Inc.) is based in Boca Raton, Florida (the Boca Raton - Fort Lauderdale area has been called "The Con Man's Capital"; said area was the base for Michael Arthur Strauss, creator of the modern advance fee racket, Clifford Noe a/k/a Dr. Noe, and countless other world class con men). They claim to be licensed to use a technology developed in the USSR, and the actual devices are said to be manufactured in one of the Russian states. Interestingly, after three years in business, they had not yet been fully trained in the use of the Russian technology. However, they do seem very interested in pushing their OTC stock. Their business model previously involved taking a percentage of increased production revenue (reportedly around 38%) after stimulation, but that model has been tried by many and has almost always failed. Shallow stripper wells do not fit into their plans. GEOTEC takes heated exception to the foregoing; see their January 25, 2001 letter. It should be clear that we are not impressed by GEOTEC, but you can visit their site and draw your own conclusions.
Microfrac Technologies Corp. (e-mail link only), a/k/a Western Technologies, offers the Microfrac Stimulation Tool. There is a short article on this in the PTTC publication, Network News (third quarter, 2000). Thiokol (of space shuttle O ring fame) is said to be the supplier of the chemistry, reportedly principally Ammonium Perchlorate. A Texas distributor quoted a 10 foot tool at $6,800.00, but see their
Pricing / Joint Venture Page; and see their
Three Pages of Questions & Answers for more information in general (please note that the 72 questions and answers were furnished by Microfrac).
Propellant Fracturing & Stimulation, LLC (PFS) acquired the patents of R P Frac, no longer in business. Their products include both a stand-alone propellant cartridge, and a hybrid device intended to be run with perforating guns. As of February, 2001, they had run approximately 15 jobs and reported good results. One of the principals, Dr. Richard S. Passamaneck has done extensive work in the propellant field. They claim to have a superior ignition system that lights the propellant from the outside (most propellant devices ignite the propellant from the center, often with nothing more sophisticated than primacord). They further claim to be able to model the behavior of their product better because of the predictability of their ignition system, and they offer a computer modeling program Their full scale devices are not priced for the stripper well market, though they were offering a smaller scale device in the $5,000.00 price range.
EnerFrac operated out of the Fort Worth, Texas area. A former user of the Microfrac devices was instrumental in the development of the EnerFrac approach. Their website is inactive, and the status of the company is unknown as of early 2007.
Sigor Corporation offers the SWTorpedo Tool. The SWTorpedo uses small charges of conventional high explosives, and is thus technically not an HEGF device. Signor indicates they assemble the charges in stages, positioning the charges, and tailoring the time delay between two or three stages based on rock properties. Signor further states their technology was developed with financial assistance from various governmental entities, and became commercially available in May, 2003. We find their discussion of rock dilatancy confusing since its application to real world well stimulation is unproven.
Exercise extreme caution when working with explosives. Stay alert and THINK; complacency kills! Follow the guidelines in the American Petroleum Institute (API) Recommended Practices for Oilfield Explosives Safety, RP 67.