Well Stimulation Using Safe Proprietary Custom Solid Rocket Propellant
RocketFrac’s disruptive patent-pending technology solution leverages decades old proven propellant fracing techniques.
Mechanics of Propellant vs Hydraulic Fracture Propagation
Fracturing with solid rocket propellant uses similar principles as conventional hydraulic fracturing: exert tremendous pressure in order to break rock. However, rather than pumping water from the surface to create pressure, propellant fracturing generates high-pressure gases through the controlled burn of solid rocket propellant.
Despite the apparent similarities in methodology, research shows that the different time-scales involved with each approach lead to a significant difference in the mechanics of fracture propagation.
Legacy Propellant Methods
Solid rocket propellant has been used by the aerospace industry since the 1940’s, and was first applied to vertical well stimulation in the 1970’s.
Current propellant fracturing methods use legacy fuels originally engineered for the aerospace industry. Due to their characteristics, these legacy propellants feature very short treatment durations – generally milliseconds up to one second – to achieve the high pressure rise rate necessary to open multiple radial fractures. The fast burn rate, however, is not able to continue fracture growth due to the rapid burn-out, and without the right containment tool to isolate the target zone, significant energy is lost at the wellbore.
Propellant Fracing Performance
Propellant fracing has been used commercially for four decades with well-known and understood performance characteristics.
- Controlled burn of solid propellant generates high pressure only at the target zone for improved permeability
- Fractures are propagated by stress waves, which rebound from rock boundaries and isolate fractures to zone of interest
- Opens 4-8 radially distributed fractures, leading to a greater connectivity with the formation
- No need for proppant to maintain open fractures.
Typical multi-radial propellant fracture pattern
Typical bi-radial hydraulic fracture pattern
Validated self-propping mechanisms:
- Scouring: 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.
- 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.
- 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.
Historical Challenges to Improving Performance
Based on the known operational parameters, in order to improve performance, several key advancements were needed.
- Wellbore sealing mechanisms to provide full event containment
- Controlled pressure rise time to initiate desired fractures
- Extended event duration to provide for extended fracture propagation
- Reformulated propellant to provide for safe and environmentally responsible operation
RocketFrac Innovations / Refinements / Improvements
RocketFrac’s solution addresses each of these challenges to improving performance. Our patent-pending solution offers several innovations compared to current propellant fracturing technology:
- Patent-pending downhole tool with integrated zone/stage isolation mechanism
- Proprietary propellant formulated for:
- precise pressure gradient and duration characteristics
- environmentally safe by-products
RocketFrac’s proprietary propellant maintains critical pressure rise rate intended to open multiple fractures and is designed with an optimized total burn time to maximize fracture growth. Combined with RocketFrac’s patent-pending isolation tool, the application ensures that exhaust gases are directed horizontally into the formation, and not lost through the wellbore.
Comparison of Fracturing Methods
| wdt_ID | Description | RocketFrac | Current Propellant | Hydraulic |
|---|---|---|---|---|
| 1 | Pressure Event Duration | Up to 20 seconds | 300 - 500 milliseconds | 10 - 100 minutes |
| 2 | Peak Pressure | 30,000 PSI | ~20,000 PSI | Minimum pressure (~5,000 PSI) to overcome overburden on the formation |
| 3 | Fractures Opened | High and low cohesion fractures and new fractures | High and low cohesion fractures, new fractures | Only lowest cohesion fractures |
| 4 | Fracture Pattern | 4-8 radial fractures | 4-8 radial fractures | 2 radially opposed fractures |
| 5 | Fracture Length | Up to 30 m | Up to 6 m | Up to 30 m |
| 6 | Well Types | Vertical and horizontal wells | Vertical wells | Vertical and horizontal wells |
| 7 | Applications | New wells, re-entries and damaged completions | Re-entries/re-stimulation | New wells, re-entries (with specialized casing) |
| 8 | Water Requirement | Only existing well bore fluids | Only existing well bore fluids | Average of 5 million gallons/well |
| 9 | Proppant Requirement | Self-propping | Self-propping | 2,500,000 – 20,000,000 pounds of sand / well |