Proppants are essential to the success of most hydraulic fractures and often account for the overwhelming cost of the treatment. Both the mass of proppant and the selection of the right type of proppant are important elements in gaining the highest Net Present Value (NPV).

It has been generally believed that in the lower closure stress environment (below 6,000 psi, i.e., shallow reservoirs), natural sands such as Brady and Ottawa are appropriate as proppants and, for the same mesh size, they provide essentially the same permeability. A commonly accepted notion is that manmade proppants (such as ceramics) should be applied at higher closure stress environments, invariably, deeper reservoirs.

The characteristics of most shale plays are very different, mainly as regards to the rock stiffness, exemplified by the Young’s Modulus, stress anisotropy/isotropy and the existence of natural fracture network. Fracture strategies in shale formations are very different. This study presents fracture designs based on three types of proppants for shale formations: Brady sand, Ottawa sand and ceramic. Permeability tests and crush tests under certain pressure range are done to determine experimentally the dimensioned fracture conductivity. A fracture optimization p-3D model is used to maximize well performance by optimizing fracture geometry, including fracture half length, width and height. Reduced proppant pack permeability is compensated by larger width. Non-Darcy effects in the fracture are also considered for gas reservoirs. Post-treatment well performance is then estimated, using the optimized well geometry, leading to cumulative production over the well life. NPV analysis is employed as the criterion to select the best proppant for the job. Finally, the completion and production data from example wells will be analyzed for comparison purpose.

In this work, we try to correct the prejudice that natural sand proppants cannot be applied to deeper reservoirs by showing NPV study results that are superior to those of manmade proppants. Keeping stimulation costs down, natural sands proppants have a much larger range of applicability than previously thought.

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