GasGun vs. Explosive
How does the GasGun compare with stimulations using high explosives?
High explosives, such as nitroglycerine or gelatin, detonate and create a shock wave. Pressures created are extremely high but last only a few microseconds (see figure below).
Extensive research has shown that the pressure pulse created by high explosives enlarges the wellbore by crushing and compacting the rock. The enlarged wellbore is left with a zone of residual compressive stress. These residual stresses and compacted rock can actually reduce permeability near the wellbore. Extensive cavings often fill the wellbore with debris that require days, even weeks, to clean up. High explosives are limited to open hole completions.
The solid propellant used in the GasGun does not actually detonate; it deflagrates. Deflagration is basically a burning process that takes place without any outside source of oxygen. Gas pressures in the range of 20,000 psi are produced that last approximately 10 milliseconds. No shock wave is produced, the rock is split rather than compacted, and multiple fractures are created. The GasGun produces large volumes of gas under high pressure that rapidly extend the fractures into the formation. There are little or no cavings, the integrity of the wellbore is maintained, and cleanup is usually minimal. The well can usually be put back on production immediately. The GasGun can be used in both open hole and perforated pipe completions.
Advantages – GasGun vs. Explosives
- No compaction zone or stress cage
- Pressures last longer for maximum fracture penetration
- Can be used in perforated casing
- Less cleanup – immediate production
- Predictable results
- Easier and safer handling