Propellant Fracturing - The Concept

Mechanics of Hydraulic vs. Propellant Fracturing

Although hydraulic and propellant fracturing both work based on the application of high pressures to the formation, past research has shown that the time-scales involved lead to a difference in the mechanics of fracture propagation.

Propellent Fracturing Hydraulic Fracturing
Solid propellant is ignited to generate a specific volume of gas. This controlled burn rapidly creates the high pressure required to create new fractures in the rock. Hydraulic fracturing introduces fractures along existing zones of weakness in the rock formation by pumping water into the wellbore under high pressure.
Fractures are propagated by stress waves, which rebound from rock boundaries and isolate fractures to zone of interest. Existing fractures are "lifted" open by water pressure. Permeability is more isolated and difficult to direct as water will follow the path of least resistance.
The high pressure rise rate creates an oval fracture zone of 4-8 radial fractures. Fracture pathways are usually linear and expand in two radially opposing directions.
Local disaggregation removes the need for proppant. Requires a proppant (sand) to hold fractures open.

Propellant Fracturing generates 140,000 kPa (20,000 PSI) in 10-1000 milliseconds

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

Tailored to Application

Typical Pressure Trace

The ability of propellant fracturing to rapidly generate high pressures allow for tailorability not available with hydraulic fracturing, due to physical limits on the pumping rate of water. Solid Propellant is a cornerstone of the space program, and is well understood and infinitely tailorable. Propellant fracturing is the only well fracturing process that can be designed to anticipate the existing stress field and produce the desired fracture pattern. It is readily adaptible, and can be easily modified or fabricated for different lithologies or pressure regimes, as necessary. Additionally, a variable burn rate can be designed to create multiple stress waves for more efficient fracturing.

Current propellant fracturing methods have only made use of the high pressure rise rates, but have not been able to take advantage of the other capabilities of solid propellant due to an inability to confine the pressures to the target zone for treatment durations of more than a few milliseconds. These methods efficiently open multiple fractures, but cannot achieve significant penetration into the formation. RocketFrac will overcome these limitations by isolating the target zone and extending treatment duration, thereby causing extended fracture growth.

Comparison of Fracturing Methods

Current Propellant PSI-CLONE™ Hydraulic
Pressure Event Duration 300-500 milliseconds 1-20 seconds 10-100 minutes
Peak Pressure 20,000 PSI 20,000 PSI ≤ Pcrit of formation*
Fractures Opened High and low cohesion 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 Short Long Long
Applications Vertical wells Vertical and deviated wells Vertical and deviated wells
Applications Re-entries/re-stimulation New wells, re-entries and damaged completions New wells, re-entries (with specialized casing)
Water Requirement In situ water only In situ water only Average of 5 million gallons per well
Proppant Required Self-propping by local disaggregation Self-propping by local disaggregation 300,000 - 4 million pounds of sand

*Defined as the minimum pressure to overcome overburden on the formation.

Damage to surface casing or other completions issues (i.e. blown out heel) typically prevents fracturing as critical casing sections can no longer contain the pressure necessary to fracture the formation. By isolating pressure application to only the target zone, PSI-CLONE™ can be used in previously un-treatable wells.