- Quantitative Evaluation of Completion Techniques on Influencing Shale Fracture ‘Complexity’
- N. Nagel ; F. Zhang ; M. Sanchez-Nagel ; D. Walls
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 25
- Discrete Element ; Mining
- Keywords: hydraulic fracturing ; discrete element mode ; shale ; numerical simulation
- Description
- In many of the active shale plays, the extremely low permeability of the shale means simple,
bi-planar hydraulic fractures do not provide enough surface area to make an economic well.
In these cases, the optimal, economic completion requires stimulation of the natural fracture
system - often called increasing the ‘complexity’ of the stimulation. A number of different
multi-well completion techniques have been proposed to enhance shale complexity. The
‘simul-frac’ technique is where companion wells are stimulated at the same location at the
same time, whereas the ‘zipper-frac’ technique employs companion wells that are stimulated
in staggered locations at the same time. The intention with these techniques is to alter either
or both the stress field and the pore pressure field to enhance the shearing of natural fractures.
In this paper, we present the results of a numerical study to quantitatively evaluate the
effectiveness of multi-well completion techniques, particularly the ‘modified zipper-frac’
technique, to optimize shale completions. The study includes a parametric study of the effects
of in-situ stress conditions, natural fracture orientation and fracture friction, and hydraulic
fracture layout on changing near and far-field natural fracture shear (complexity). Changes in
the stress field, particularly shear stress, are considered the primary means of increasing
fracture complexity. The quantitative results of the study provide a means to optimize the
application and design of different multi-well completion techniques as a function of the
presented parameters. Optimized completion designs mean lower well costs, greater produc‐
tion and, ultimately, improved well economics.
PDF |
- Fracture Network Connectivity — A Key To Hydraulic Fracturing Effectiveness and Microseismicity Generation
- F. Zhang ; N. Nagel ; B. Lee ; M. Sanchez-Nagel
- Book Title / Journal: Effective and Sustainable Hydraulic Fracturing
- Year: 2013 , Series: Chapter 28
- Discrete Element
- Keywords: hydraulic fracturing ; microseismicity ; Discrete Element Method
- Description
- In this work, the effect of fracture network connectivity on hydraulic fracturing effectiveness
was investigated using a discrete element numerical model. The simulation results show that natural fracture density can significantly affect the hydraulic fracturing effectiveness, which was characterized by either the ratio of stimulated natural fracture area to hydraulic fracture area or the leakoff ratio. The sparse DFN cases showed a flat microseismic distribution zone with few events, while the dense DFN cases showed a complex microseismic map which
indicated significant interaction between the hydraulic fracture and natural fractures. Further,
it was found that the initial natural fracture aperture affected the hydraulic fracturing effectiveness more for the dense natural fracture case than for the sparse (less dense) case. Overall, this work shows that fracture network connectivity plays a critical role in hydraulic fracturing effectiveness, which, in-turn, affects treating pressures, the created microseismicity and corresponding stimulated volume, and well production.
PDF |
