The GasGun Compared to Hydraulic Fracturing
The GasGun will never replace hydraulic fracturing. Large hydraulic fracture treatments can create a fracture hundreds, if not thousands, of feet in length. But many small pay zones in marginal wells cannot justify the expense of these treatments. The GasGun can be a very economical alternative and requires much less equipment for fielding.
Hydraulic fracturing creates a single fracture oriented perpendicular to the least principal in situ stress. Unfortunately, the fracture propagates vertically as well as laterally seeking the path of least resistance. Many hydraulic fractures have been known to break out of the producing formation and into aquifers and thief zones. While the fractures produced by the GasGun are more limited in length, gas pressures overpower the in situ state of stress, creating multiple radial fractures with minimal vertical growth. Research conducted by Sandia National Laboratories showed the vertical fracture growth to be no more than 2 ft to 5 ft above or below zone.2 As a result, GasGun fractures are much less likely to break out of the producing zone.
The multiple fractures created by the GasGun may also be much more effective than hydraulic fracturing in naturally-fractured reservoirs. Hydraulic fractures commonly propagate parallel to most of the existing fractures or "with the grain". Multiple fractures may not extend as far, but may link the well to more of the natural fractures (Figure 2).
The GasGun Compared to Other Solid Propellant Tools
The GasGun produces several times more gas and energy than most other stimulation tools using solid propellant. (Note: A 3¼” x 10’ GasGun tool delivers more than 30,000,000 ft-lb of energy.) GasGun propellant is also significantly more effective in producing fractures since it uses multi-perforated grains that are progressively burning. This means that the rate at which the propellant burns increases with time, producing gas faster as the material is consumed.
The progressive burning is much more effective in controlling peak pressures and advancing the fractures late in the process when crack volumes are the greatest. Independent research bears this out. In a study conducted by Sandia National Laboratories, a multi-perforated propellant was 300 times more effective in enhancing formation permeability than a standard solid propellant in a direct side-by-side comparison.3
Stimulating the Arbuckle Dolomite
As of July 2003, over 900 GasGun stimulations had been conducted with 240 of them in Kansas, including 70 in the Arbuckle dolomite. The majority of these wells are in Butler, Stafford, Barton and Ellis counties. One operator has conducted almost half of these Arbuckle stimulations and has developed the following simple procedure: 1) Pull rod and tubing, 2) Select GasGun length to match perforated interval, 3) Shoot GasGun with 1000-2000 feet of fluid tamp, 4) Clear debris and swab, 5) Spot 250 gallons of acid, fill to surface, and let formation take fluid on vacuum, and 6) Rerun rod and tubing and put on pump.
Economic success has been achieved in approximately 75% of the wells in which the operator was willing to share the data. A typical well was making 0-2 BOPD and 0-20 BWPD prior to treatment and 6-8 BOPD and 20-30 BWPD after GasGun stimulation and acid. Production results have shown excellent long-term sustainability.
Most of the 900 GasGun stimulations have been conducted in the Appalachian and Illinois basins and in Kansas, Oklahoma, Texas, and Alberta, Canada. Wells have ranged in depth from 200 to 10,000 feet with more than 80% being less than 3,000 feet. Some of the most successful treatments have been in formations that are known to produce large volumes of water when hydraulically fractured. Examples include the Arbuckle formation in Kansas and the Aux Vases, Cypress and Tar Springs formations in the Illinois basin. Successful stimulations have been achieved in many lithologies including sandstone (consolidated and unconsolidated), limestone, dolomite, shale, coal, chert, and chalk.
Updated February 2003