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Hydraulic Fracturing Modeling in Conventional and Unconventional Reservoirs

Javid Shiran, Behrouz | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48126 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Badakhshan, Amir; Ghotbi, Siroos; Taghikhani, Vahid
  7. Abstract:
  8. Unconventional fracturing applications such as long-term waterflooding at fracturing pressure, produced water re-injection and waterfracs, etc., are characterized by very high fluid leakoff velocity, long operation time and significant changes in stress, pore pressure, and/or permeability and porosity, affecting possibly large regions around the wellbore and/or fracture. These special characteristics make fracturing modeling methods developed for conventional fracturing applications inadequate. Some of the problems encountered include grid effects resulting in oscillation of fracture growth with time (limiting the stability of conventional fracture modeling models), singularity of material balance constraint on injected fluid and geomechanical effects caused by the changes in reservoir pressure and temperature and caused in turn by the existence and propagation of fracture. Therefore proper representation of dynamic (propagating) fractures which requires modeling the propagation in a manner coupled with reservoir response is the central issues for simulation of these unconventional fracturing processes. This work focuses on improving fracturing modeling techniques by coupling fracture propagation with reservoir simulation. The coupled models developed here intentionally use only one common stationary grid system for fracturing modeling, reservoir simulation, treat fracture as a highly-permeable part of reservoir matrix for flow simulation (using the concept of transmissibility multipliers). This research developed a transmissibility modification model to couple a static hydraulic fracture with reservoir simulation, which averages fracture and matrix transmissibility based on fracture size and permeability. This method was validated by comparing it with analytical production model of a well with infinite and finite fracture conductivity. Then, as the first step in developing a fracturing model fully coupled with reservoir, the method of coupling the static hydraulic fracture with reservoir simulation was extended to model propagating fracture by coupling reservoir model, which are computed based on length and width of a 2-D GDK-shaped fracture. Fracture length is calculated based on minimum net pressure criteria, instead of the conventional material balance constraints of injected fluid directly while fracture width is calculated according to the 2-D analytical GDK formula. Four different mathematical approaches are derived to calculate transmissibility multiplier for the fractured grids by averaging fracture and matrix transmissibility based on fracture and grid sizes. This method was extended to model propagating fracture by pressure-dependent or stress-dependent dynamic transmissibility multiplier and was further implemented into a modular coupled (finite difference) reservoir simulator
  9. Keywords:
  10. Modeling ; Hydraulic Fracturing ; Conventional Reservoirs ; Uncomventional Reservoirs

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