At its most basic, fracturing with solid rocket propellant uses similar principles as traditional hydraulic fracturing: exert tremendous pressure in order to break rock. However, rather than pumping water from the surface to create the pressure, propellant fracturing generates high pressure gases through the controlled burn of solid rocket propellant right at the target zone. More importantly, despite the apparent similarities in methodology, past research has shown that the time-scales involved lead to a significant difference in the mechanics of fracture propagation.
|Propellant Fracturing||Hydraulic Fracturing|
|A controlled burn of solid propellant rapidly generates high pressure only at the target zone.||Quasi-static operation where pressure is generated by pumping fluids from the surface at a relatively low rate.|
|Fractures are propagated by stress waves, which rebound from rock boundaries and isolate fractures to zone of interest.||Fractures are "lifted" open by fluid pressure in excess of formation pressure. Fracture growth is dominated by stress field.|
|Opens 4-8 radially distributed fractures, leading to a greater connectivity with the formation.||Fracture pathways are usually linear and expand in two radially opposing directions, leading to isolated zones of permeability.|
|No need for proppant to maintain fractures (see below).||Requires a proppant (sand) to hold fractures open and maintain permeability.|
Besides removing the need for water, another extremely appealing economic and environmental benefit to propellant fracturing is that it has multiple "self-propping" mechanisms. Mineback and laboratory experiments have shown three separate effects of propellant fracturing that prevent permeable pathways from re-closing after the treatment:
|Local disaggregation||Rapid loading and fracture opening causes minor disaggregation or "rubbilization" at the fracture face. These small particles prevent fracture closure and act as a locally derived proppant.|
|Fracture Erosion||High-temperature, high-speed exhaust gases result in a scouring effect that erodes the fracture surfaces. This erosion results in opposing fracture surfaces having dissimilar geometries.|
|Shear Dislocation||Some mineback experiments have shown shear dislocation in which the opposing fracture surfaces close offset to each other. This offset closure results in permeable pathways remaining open.|
Solid rocket propellant has been a cornerstone of the aerospace industry since the 1940's. It has been used extensively in surface-to-orbit launch vehicles and demonstrates consistent and predictable performance. Solid propellant was first applied to well stimulation in the late 1970's, and industry participants have claimed hundreds of successful treatments in vertical wells. RocketFrac's patent pending tool will now allow the application of solid rocket propellant in horizontal wells.
Current propellant fracturing methods have made use of legacy solid propellants tailored towards launch vehicles and missiles, resulting in a very short treatment duration, on the order of milliseconds. They achieve the high pressure rise rate necessary to open multiple radial fractures, but are not able to continue fracture growth due to the rapid burn-out. Additionally, without RocketFrac's unique capability to isolate the target zone, significant energy is lost to the wellbore.
RocketFrac employ's a proprietary custom blend of propellant specialized for well stimulation. It will maintain the critical pressure rise rate to open multiple fractures, but is designed with an optimized total burn time to maximize fracture growth. The new propellant is combined with RocketFrac's proprietary state-of-the-art isolation method to ensure exhaust gases are directed into the formation.
|Pressure Event Duration||1-20 seconds||300-500 milliseconds||10-100 minutes|
|Peak Pressure||30,000 PSI||25,000 PSI||≤ Pcrit of formation*|
|Fractures Opened||High and low cohesion, new fractures||High and low cohesion, new fractures||Only lowest cohesion fractures|
|Fracture Pattern||4-8 radial fractures||4-8 radial fractures||2 radially opposed fractures|
|Fracture Length||Up to 30 m||Up to 6 m||Up to 30 m|
|Applications||Vertical and horizontal wells||Vertical wells||Vertical and horizontal wells|
|Applications||New wells, re-entries and damaged completions†||Re-entries/re-stimulation||New wells, re-entries (with specialized casing)|
|Water Requirement||Well bore fluids only||Well bore fluids only||Average of 5 million gallons per well|
|Proppant Required||Self-propping||Self-propping||2.5 - 20 million pounds of sand|
*Defined as the minimum pressure to overcome overburden on the formation.
†PSI-CLONE™ can be used in previously un-treatable wells by isolating pressure to only the target zone. Damage to surface casing or other completions issues (e.g., blown out heel) typically prevents use of other fracturing techniques as critical casing sections can no longer contain the pressure necessary to fracture the formation.