Fracture treatment design requires accurate input data to perform calculations and build reliable models. Although complete data is preferred, it is often not available. In practice, engineers use the best available data and may rely on correlations or ranges of values due to uncertainty. Validation of input data is important to ensure reliable results.
- Mechanical and Elastic Properties
Poisson’s ratio and Young’s modulus are key mechanical properties used in fracture design. These properties are commonly obtained from well logs, using correlations based on compressional (P-wave) and shear (S-wave) travel times. They can also be measured directly from core samples.
Hydraulic fracturing involves rock deformation. Therefore, dynamic Young’s modulus obtained from logs is typically converted to static Young’s modulus for fracture calculations. This conversion is done using correlations based on laboratory measurements or previous studies. Conversion of Poisson’s ratio is generally not required because the dynamic and static values are similar.
- Stress Data
Stress profiles are required to model fracture growth. These profiles can be obtained directly from well logs. If log data are unavailable or unreliable, stresses can be estimated using correlations based on other log measurements such as gamma ray, density, neutron porosity, and resistivity. These correlations are usually specific to a given formation and may introduce additional uncertainty.
- Reservoir Pressure and Transmissibility
Reservoir pore pressure is a critical input for fracture design. It can be determined using drillstem testing, repeat formation testing, or pressure buildup analysis after shut-in periods.
If pressure buildup data are not reliable, injection falloff testing can be used. This includes diagnostic fracture injection tests (DFIT). Perforation inflow testing can also be used to estimate reservoir pressure and transmissibility by analyzing pressure behavior.
Reservoir transmissibility () can be derived from these tests and is important for evaluating fluid flow in the reservoir.
- Additional Reservoir and Formation Data
Additional parameters are required to fully characterize the reservoir and design the treatment. These include bottomhole temperature, permeability, fluid saturation and properties, porosity, rock density, and net pay thickness.
Overall, due to uncertainty in available data, fracture treatment design often relies on ranges of values rather than single values. Input data must be validated and calibrated using field measurements whenever possible.
