Abstract
Abstract: In recent years, multi-stage hydraulic fracturing technologies have greatly facilitated the development of unconventional oil and gas resources. However, a quantitative description of the “complexity” of the fracture network created by the hydraulic fracturing is confronted with many unsolved challenges. Given the multiple scales and heterogeneity of the fracture system, this study proposes a “bifurcated fractal” model to quantitatively describe the distribution of induced hydraulic fracture networks. The construction theory is employed to generate hierarchical fracture patterns as a scaled numerical model. With the implementation of discrete fractal-fracture network modeling (DFFN), fluid flow characteristics in bifurcated fractal fracture networks are characterized. The effects of bifurcated fracture length, bifurcated tendency, and number of bifurcation stages are examined. A field example of the fractured horizontal well is introduced to calibrate the accuracy of the flow model. The proposed model can provide a more realistic representation of complex fracture networks around a fractured horizontal well, and offer the way to quantify the “complexity” of the fracture network in shale reservoirs. The simulation results indicate that the geometry of the bifurcated fractal fracture network model has a significant impact on production performance in the tight reservoir, and enhancing connectivity of each bifurcate fracture is the key to improve the stimulation performance. In practice, this work provides a novel and efficient workflow for complex fracture characterization and production prediction in naturally-fractured reservoirs of multi-stage fractured horizontal wells.
Highlights
It has been commonly recognized that significant spatial heterogeneity, characterized by the multi-scale nature, extensively exists in shale reservoirs
It is defined that the stimulated reservoir volume (SRV) of the secondary branching fractures and fracture network gradually decrease with the fracture propagation and, we introduced the concept of the stimulated fracture volume (SFV)
The numerical model built for the representative element volume of the fracture is applied to estimate the performance following every iteration stage, which assumes that the homogeneous reservoir and each staged fractal fracture are open, and the existing natural fractures are not modeled
Summary
It has been commonly recognized that significant spatial heterogeneity, characterized by the multi-scale nature, extensively exists in shale reservoirs. The wetting properties and flow behavior of oil and gas change dramatically in different types of porous media. Cross-scale nano-micro porosity plays a dominant role in fluid storage, and micro-scale pore-throat morphology and connectivity strongly affected fluid transport phenomena. The fracture growth and the occurrence of natural fractures are extremely complex. Macro-scale favored flow areas are, derived from the multi-scale
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