Mechanical Properties of Unconsolidated Sands and their Impact on Frac-Pack Design

by
Edouard Wang, MSE

University of Texas at Austin, 1996
Supervisor: Mukul M. Sharma

The practice of hydraulic fracturing has recently been applied to unconsolidated sands. Pre-existing models for fracture design are based on the assumption that the rock behaves elastically, which is true for hard and tight rocks. However, there is evidence that unconsolidated sands exhibit non-elastic behavior to a very significant degree. This can have a significant impact on fracture design in unconsolidated sand reservoirs.

The static mechanical properties of unconsolidated sands were measured by biaxial testing of a variety of samples under different conditions. The elasto-plastic behavior of the sands was studied. The Young's modulus and Poisson's ratio inferred from the data show systematic trends with stress, fluid saturation, grain size and grain shape.

A preliminary study of the geometry of fractures in unconsolidated media was conducted. Some unique aspects of fracture growth in unconsolidated sands such as their elasto-plastic nature and the possibility of shear failure can significantly affect the geometry of the fracture.

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