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An embedded fracture modeling framework for simulation of hydraulic fracturing and shear stimulation

A numerical modeling framework is described that is able to calculate the coupled processes of fluid flow, geomechanics, and rock failure for application to general engineering problems related to reservoir stimulation, including hydraulic fracturing and shear stimulation.

7 Discussion and concluding remarks

In this work, we developed a novel numerical modeling framework based on the embedded fracture modeling (EFM) approach as an effective technique to model reservoir stimulation processes such as hydraulic fracturing and shear stimulation. The EFM approach was implemented in a reservoir model that couples fluid flow, mechanical deformation, and rock failure processes. In order to verify the accuracy of the embedded fracture model, the present model was compared to a more traditional discrete fracture model (DFM) in three separate numerical examples. In each example, the EFM performed rermarkably well and yielded results that matched the DFM to within an acceptable margin of error.

In this paper, we demonstrated that the EFM is extremely well-suited for fracture propagation problems. In the EFM framework, newly formed fracture control volumes can be integrated into the numerical model with relative ease. The ability to discretize the fracture and matrix rock domains separately ensures that fractures are able to propagate without the numerical constraints associated with traditional approaches that employ conforming meshes. We showed that it is possible to coarsen the matrix discretization and still obtain a reasonable degree of accuracy using the EFM approach. Once a fracture discretization has been defined for a DFM, however, it is very difficult to arbitrarily coarsen the matrix discretization in the same fashion that is possible with EFM. This has important implications when moving towards increased problem complexity, for instance, when considering interaction between propagating fractures and natural fractures, branching and curving fractures, or three dimensions. Issues associated with numerical discretization in these complex scenarios can set practical limitations on the utility of reservoir modeling, and are largely overcome in the EFM framework.

Two approximate models were also developed and compared to both EFM and DFM. These models are referred to as the one-dimensional leakoff and zero leakoff approximation models, and were observed to provide useful constraints on reservoir stimulation behavior at significantly reduced computational effort. For very low matrix permeabilities, all models were observed to provide similar results. As matrix permeability increased, the two approximate models diverged from the EFM and DFM models. Further investigation must be performed in order to better classify the range of geologic and operational parameters over which each of the models retain a high level of accuracy.

It has become clear that geomechanics can play an important role in many different facets of reservoir engineering practice. For example, mechanisms that enable permeability creation during hydraulic fracturing are controlled largely by mechanical effects. Shear slip events commonly observed during microseismic monitoring operations of fluid injection treatments help reservoir engineers define the stimulated region. The reservoir model described in this paper can be applied in practical settings to help design and optimize reservoir management strategies or in research settings to better understand fundamental reservoir processes.

Acknowledgments We thank the industrial affiliates of the Stan- ford Center for Induced and Triggered Seismicity for partial financial support of this work. The financial support of the Cockrell School of Engineering at The University of Texas at Austin is also gratefully acknowledged. The numerical simulations were performed at the Stanford Center for Computational Earth and Environmental Science (CEES) using their high performance computing (HPC) resources.


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Jack H. Norbeck
[email protected]

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Emanuel Martin
Emanuel Martin is a Petroleum Engineer graduate from the Faculty of Engineering and a musician educate in the Arts Faculty at National University of Cuyo. In an independent way he’s researching about shale gas & tight oil and building this website to spread the scientist knowledge of the shale industry.

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