Numerical Investigation of Complex Hydraulic Fracture Development in Naturally Fractured Reservoirs
- Kan Wu (University of Texas At Austin) | Jon E. Olson (The University of Texas at Austin)
- Document ID
- Society of Petroleum Engineers
- SPE Hydraulic Fracturing Technology Conference, 3-5 February, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2015. Society of Petroleum Engineers
- stress shadow effects, multiple fracture propagation, displacement discontinuity method, Complex fracture networks
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Complex fracture networks have become more evident in shale gas reservoirs due to the interaction between pre-existing natural and hydraulic fractures. Accurate characterization of fracture complexity plays an important role in optimizing fracturing design, especially for shale reservoirs with high-density natural fractures. In this study, we simulate simultaneous multiple fracture propagation in a naturally fractured reservoir using a Simplified Three Dimensional Displacement Discontinuity Method (S3D DDM). This 3d model is implemented to more accurately calculate fracture displacements and fracture-induced dynamic stress changes than our previously developed pseudo-3d model. A stochastic realization method is used to generate different natural fracture patterns based on a power law probability distribution.
Complex fracture geometry is created when multiple fractures propagate in the naturally fractured reservoirs. Width distribution of fracture networks show that fracture width is restricted on natural fractures and dilates after coming out from the natural fractures, implying that the width restriction might stop proppant and decrease effective fracture length. The growth of multiple fractures is not even, which is a function of reservoir and fracture design properties. The effects of differential stress (SHmax - Shmin), perforation cluster spacing, fracture height, Young’s modulus of the formation, and natural fracture patterns on effective fracture surface contact area and fracture complexity are investigated.
The simulation results show that (1) high differential stress reduces the complexity of fracture geometry and increases injection pressure; (2) there is an optimal choice for the number of fractures per stage to maximize effective fracture surface area, beyond which increasing the number of fractures actually decreases effective fracture area; and (3) fracture complexity is a function of the length and spacing distributions of natural fractures (various regular pattern geometries are investigated). Longer natural fractures lead to wider stimulation regions, while effective fracture surface area decreases with closer natural fracture spacing. Net pressure histories are shown to be somewhat insensitive to resultant fracture geometry, illustrating to the difficulty in identifying fracture complexity based only on injection pressure. The overall sensitivity results presented should serve as guidelines for fracture complexity analysis.
|File Size||5 MB||Number of Pages||15|