Accurate Simulation of Non-Darcy Flow in Stimulated Fractured Shale Reservoirs

Abstract

Unconventional shale gas reservoirs require stimulation via hydraulic fracturing of pre-existing fracture networks for practical exploitation, creating a stimulated reservoir volume (SRV). Within the SRV, gas flow from the nano-Darcy shale to the complex stimulated fracture network has been modeled in reservoir simulators using a variety of techniques which upscale/simplify the fracture network. The simulation techniques used in the past were normally not compared with reference solutions. This work investigates using finely-gridded single well reference solutions (approximately 6-14 million cells) for simulating Darcy and non-Darcy flow within an explicitly modeled SRV complex fracture network, in 2-D, with and without primary hydraulic fractures, as well as scenarios which model stress sensitive permeability and later re-stimulation of a horizontal well. The network fractures use cells which are only 0.001 ft. wide. The reference solutions are compared with standard dual permeability and MINC (multiple interacting continua) dual continua models as well as novel models which simulate flow inside of the SRV using coarse, logarithmically spaced, locally refined, dual permeability grids, and simulate flow outside of the SRV using unrefined dual permeability grids. These coarse models can be run in minutes on standard hardware, where as the reference models can take days to run on the same hardware. We will show that excellent matches to the reference solutions are possible using a modest number of refinements to simulate the flow within the SRV when the fracture permeability and the fracture Forchheimer number (for non-Darcy flow) are scaled as described in the paper. These techniques allow the use of 2.0 ft. wide fracture conduits to mimic non-Darcy flow in 0.001 ft. wide fractures. Good agreement between the reference and coarse models are observed even during the early flow period of the reservoir.

Development of an Efficient Embedded Discrete Fracture Model for 3D Compositional Reservoir Simulation in Fractured Reservoirs

“…Likewise, Fredd et al (2001) presented laboratory data showing the effect of closure stress on propped fracture conductivity for a rock with relatively high Young's modulus. Therefore, recent studies such as Rubin (2010) and Cipolla et al (2010) used specific closure-stressconductivity tables in the simulation of unconventional reservoirs to account for the dynamic behavior of hydraulic fractures. Closure stress acting on the hydraulic fracture is defined as the horizontal stress perpendicular to the fracture minus the pressure inside the fracture.…”

Effect of Fracture Design Parameters on the Well Performance in a Hydraulically Fractured Shale Gas Reservoir

“…To make the model of the hydraulically fractured shale reservoir, the number of grid blocks should be large enough. However, as it takes lots of time, the LS (logarithmically spaced) and LR (locally refined) model had been proposed (Rubin, 2010). The LS-LR model presented similar results with shorter simulation time compared to a fine gridding model.…”

The Optimization of Fracture System Conductivity in Tight Oil Reservoirs

“…Barry Rubin [11] compared the classical DK model, the MINC (multiple interacting continua) model and the DK-LS-LGR model in simulating network fracturing in shale gas reservoirs. The results demonstrate that the DK-LS-LGR model can best characterize the complex fracture system.…”

“…This paper combines the work of Cipolla in fracture performance evaluation in unconventional gas reservoirs, and the work of Barry Rubin in fracture network simulation [11]. By applying the proppant distribution hypothesis to horizontal well network fracturing, a typical simulation model is established.…”