# Category: OptiFrac

## Contents

## Brief

** optiFrac** is a single well fracture design optimization software.

For the given set of reservoir and proppant properties ** optiFrac** calculates maximum achievable well productivity index (JD) and required fracture geometry.

In production optimization of hydraulic fracturing, it is important to recognize that for a fixed proppant volume, fracture length and fracture width compete to each other. Consequently, there is an optimum fracture length and width that would maximize the dimensionless productivity index of the fractured well ^{[1]}. **Unified Fracture Design** provides a methodology whereby for any given proppant volume the best combination of width and length could be determined ^{[2]}.

** optiFrac** is available online at www.pengtools.com and in AppStore for iPad.

## Typical applications

- Optimization of hydraulic fracturing with
**Unified Fracture Design**^{[2]} - Calculating
**optimum**fracture design parameters:- Dimensionless productivity index,
**J**._{D} - Dimensionless fracture conductivity,
**C**._{fD} - Fracture half length,
**x**._{f} - Fracture width,
.**w**_{f} - Fracture penetration,
**I**._{x}

- Dimensionless productivity index,
- Understanding post-fracturing production performance
- Sensitivity studies

## Math & Physics

- - penetration ratio
^{[2]},

- - dimensionless fracture conductivity
^{[2]},

- - proppant numer
^{[2]},

- - pseudo-steady state equation for finite-conductivity fractured wells
^{[1]},

- - steady state equation for finite-conductivity fractured wells
^{[1]},

- - shape factor
^{[1]}.

## Type Curves

The Type Curves shows the dimensionless productivity index, **J _{D}**, at steady and pseudo-steady state as function of

**C**, using

_{fD}**I**as parameter (red curves) and overlapping with the type curve with

_{x}**N**as parameter (black curves).

_{p}The green curve along the maximum points for different **N _{p}** values is “Design Optimization Curve”

^{[1]}. This curve represents the target of the designs of the fracture treatments in a dimensionless form.

Type Curves were obtained, through seven hundred runs with a numerical simulator, modeling a fractured well in a closed square reservoir ^{[1]}. For infinite and finite fracture conductivities, the shape factors, **C _{A}**, can be calculated if the

**P**is known for a specific value of

_{D}**I**. The

_{x}**P**value obtained by numerical simulations. After knowing

_{D}**C**(which would be a function of

_{A}**I**), f-function values can be calculated if

_{x}**P**is known for a specific dimensionless fracture conductivity

_{D}**C**and fracture penetration

_{fD}**I**.

_{x}## Flow Diagram

## Workflow

1. Calculate the **N _{p}**:

- the volume of the reservoir

- the fracture permeability

- the proppant mass in the pay zone

- the fracture volume in the pay zone

- the proppant number

2. Read **C _{fD}^{opt}**,

**I**,

_{x}^{opt}**J**from the Design Optimization Curve of the Type Curve

_{D}^{opt}3. Calculate optimum fracture half-length and width:

## Physical Constraints

It is important to mention that the Design Optimization Curve could give unrealistic fracture geometry depending on the reservoir permeability, reservoir mechanical properties and target **N _{p}**. The two most common scenarios are

^{[1]}:

- The required net pressure for the fracture geometry is too high - “maximum net pressure curve”,
- Fracture width is too small (fracture too narrow) - “minimum width curve”.

The area between the “minimum width curve” and the “maximum net pressure curve” is the “working area” (highlighted in yellow) of the whole type curve for the specific rock mechanical properties, reservoir and proppant properties used. Any fracture design for this specific case should be located on the “optimum design curve” anywhere in this working area depending on the desired **N _{p}**

^{[1]}.

#### Maximum net pressure

The maximum net pressure during the fracturing treatment should provide a surface pressure less than a certain value (which is surface pressure operational limit) ^{[1]}.

#### Minimum fracture width

Fracture propped width should be greater than N times mean proppant diameter (to provide at least N proppant layers in the fracture after closure)^{[1]}. N=3 in the ** optiFrac**.

## Main features

- Fracture design Type Curves (Plot of
**J**as a function of_{D}**C**using_{fD}**I**and_{x}**N**as parameter)._{p} - Design Optimization Curve which corresponds to the maximum
**J**values for different_{D}**N**._{p} - Design Optimum Point at which
**J**is maximized for the given proppant, fracture and reservoir parameters._{D} - Physical constraints envelope.
- Hydraulic fracturing proppant catalog with predefined proppant properties.
- Users Data Worksheet for benchmarking vs actual.
- "Default values" button resets input values to the default values
- Switch between Metric and Field units
- Save/load models to the files and to the user’s cloud
- Share models to the public cloud or by using model’s link
- Export pdf report containing input parameters, calculated values and plots
- Continue your work from where you stopped: last saved model will be automatically opened
- Download the chart as an image or data and print (upper-right corner chart’s button)
- Export results table to Excel or other application

## Nomenclature

- = dimensionless fracture conductivity, dimensionless
- = shape factor, dimensionless
- = Young's Modulus, psia
- = f-function, dimensionless
- = proppant permeability reduction due to gel damage, %
- = height, ft
- = penetration ratio, dimensionless
- = dimensionless productivity index, dimensionless
- = permeability, md
- = mass, lbm
- = dimensionless proppant number, dimensionless
- = dimensionless pressure (based on average pressure), dimensionless
- = net pressure, psia
- = specific gravity, dimensionless
- = volume, ft
^{3} - = width, ft
- = drainage area, ft
^{2} - = fracture half-length, ft

### Greek symbols

- = dry to wet width ratio at the end of pumping, usually 0.5-0.7
- = geometric factor in vertical direction, 0.75 for PKN model, 1 for KGD model
- = Poisson's ratio, dimensionless
- = porosity, fraction
- = 3.1415

### Superscripts

- opt = optimal
- pss = pseudo-steady state
- ss = steady state

### Subscripts

- e = external
- f = fracture
- gross = gross
- max = maximum
- net = net
- prop = proppant
- r = reservoir

## References

- ↑
^{1.0}^{1.1}^{1.2}^{1.3}^{1.4}^{1.5}^{1.6}^{1.7}^{1.8}^{1.9}Rueda, J.I.; Mach, J.; Wolcott, D. (2004). "Pushing Fracturing Limits to Maximize Producibility in Turbidite Formations in Russia" (SPE-91760-MS). Society of Petroleum Engineers. - ↑
^{2.0}^{2.1}^{2.2}^{2.3}^{2.4}Economides, Michael J.; Oligney, Ronald; Valko, Peter (2002).*Unified Fracture Design: Bridging the Gap Between Theory and Practice.*Alvin, Texas: Orsa Press.

## Pages in category "OptiFrac"

The following 6 pages are in this category, out of 6 total.