RocketFrac Propellant Fracturing - The Concept

Mechanics of Hydraulic vs. Propellant Fracturing

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 FracturingHydraulic 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.

Propellant fracturing generates ~205,000 kPa (~30,000 PSI) in 100-500 msec

Propellant Fracture Diagram
Typical multi-radial propellant fracture pattern

Hydraulic fracturing generates ~35,000 kPa (~5,000 PSI) in 1-10 hours.

Hydraulic Fracture Diagram
Typical bi-radial hydraulic fracture pattern

Self-Propping Mechanisms

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 disaggregationRapid 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 ErosionHigh-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 DislocationSome 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.

Propellant Application

Typical Pressure Trace

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.

Comparison of Fracturing Methods

PSI-CLONE™Current PropellantHydraulic
Pressure Event Duration1-20 seconds300-500 milliseconds10-100 minutes
Peak Pressure30,000 PSI25,000 PSI≤ Pcrit of formation*
Fractures OpenedHigh and low cohesion, new fracturesHigh and low cohesion, new fracturesOnly lowest cohesion fractures
Fracture Pattern4-8 radial fractures4-8 radial fractures2 radially opposed fractures
Fracture LengthUp to 30 mUp to 6 mUp to 30 m
ApplicationsVertical and horizontal wellsVertical wellsVertical and horizontal wells
ApplicationsNew wells, re-entries and damaged completionsRe-entries/re-stimulationNew wells, re-entries (with specialized casing)
Water RequirementWell bore fluids onlyWell bore fluids onlyAverage of 5 million gallons per well
Proppant RequiredSelf-proppingSelf-propping2.5 - 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.