How FastFrac works

FastFrac designs a hydraulic fracture treatment one stage at a time. You enter the well, the reservoir, the rock, the fluid, the proppant and the pumping schedule; it solves the fracture geometry stage by stage and reports the treatment schedule, the pressures and horsepower, and where each stage of sand ends up in the fracture.

Everything below follows the order you work in.

1. Start

On the home page, press Start a new design.

The input page opens with a worked example already filled in, a Marcellus Shale well, so you can see a complete design immediately. Change any value you like, or press Select design to reload it or to open a design file from your computer.

2. Fill in your data

The input page is a set of panels, each with a dot that turns amber when something in it is outside its allowed range:

• Design identification. Well ID, who prepared it, and the company. The Well ID titles every page and names the file when you save.
• Well and completion data. Well type, depth, casing, grade, annulus back pressure, the fracturing path, the number of primary parallel fractures, the complexity adjustment, and the perforations. Leave Well type on Vertical and one depth does everything. Choose Horizontal and two more fields appear: the true vertical depth, which sets the hydrostatic head, the fracture pressure and the reservoir pressure, and the liner ID through the lateral, which defaults to the casing ID. The measured depth is then the length of pipe to the stage being treated, and it sets the friction and the wellbore volume, so each stage along a lateral is run as its own design. Computed values include the casing burst rating, the effective parallel-fracture count, and the displacement volume; these are calculated from the entered inputs.
• Reservoir data. Net pay, permeability, porosity, reservoir fluid viscosity, total compressibility, pressure gradient and temperature.
• Rock mechanical properties. Young's modulus, Poisson's ratio, fracture gradient, and the containment height. Set the containment height to zero and the fracture is treated as radial rather than confined.
• Fracturing fluid properties and Proppant properties.
• Treatment design. The injection rate, and the pumping schedule itself.

In the pumping schedule, each row is a stage with a name, a slurry volume and a sand concentration. Add stage appends a row, the × at the end of a row removes it, and the tick in the Disp. column marks the displacement, the clean fluid that pushes the last slurry to the perforations.

The optional Fracture complexity adjustment (%) lets you explore a higher effective fracture count without changing the number of perforations. Leave it at 0% to apply no adjustment. See the Input Guide for details.

3. Use the Toolbox if you need it

Four inputs are often not known directly. Press Toolbox on the input page.

• Reservoir fluid viscosity and total compressibility are computed from PVT correlations. Enter reservoir pressure and temperature, choose oil or gas, and give the fluid properties and the saturations. Each result has a Use in design button that writes the value straight into the design.
• Young's modulus and Poisson's ratio have reference tables by rock type and formation, also with Use in design buttons. These are typical values for a first estimate, not measurements.

Toolbox basis shows every equation the Toolbox applies, its range of validity and its source. Back to Toolbox returns from it, and Back to design returns to the input page.

Values the Toolbox produced are saved with your design, so you can reopen it later and see exactly which inputs they came from.

4. Run the design

Press Continue to results. If anything is out of range, the first offending field is focused instead, so nothing is computed from a value the model cannot use.

The results have three tabs.

Schedule is the treatment schedule: for every stage, the time, the clean and slurry rates, the sand concentration, stage and cumulative volumes and sand, the surface pressure and hydraulic horsepower, and the fracture as it stands at the end of that stage, half length, created width and proppant fill. Above the table is a strip of summary figures for the job as a whole.

Graphics draws the fracture. The geometry figure shows where every stage ends up at the end of pumping, from the pad at the tip to the last slurry at the wellbore, with how much of each stage is still in the fracture after leakoff. The width profile compares created width with propped width along the fracture.

Use the chart selector to view Pressure, Fracture Growth, or Slurry Retained. The selected chart is included when you print or save the report as a PDF.

Basis sets out the model: the equations in the order the engine applies them, what each symbol means, the assumptions, and the sources. The Basis page is never printed.

5. Keep the result

Print / Save as PDF, on the results and graphics pages, produces the complete report: inputs, schedule, figures and the limitations. It is laid out for letter paper.

Save design writes the whole design, inputs, schedule and Toolbox inputs, to a file on your computer. Select design opens one again. Designs are not stored on our servers; the only copy is yours, except for an in-progress draft your own browser keeps so you can close the tab and come back to it.

Back to input returns to the inputs, and Home returns to the start.