Permeability of fracture filled or not with proppants under in situ effective stress condition is a key parameter for optimization of proppant recipe used in hydraulic fracturing job. Furthermore, fracture permeability impacts results of numerical modelling of Stimulated Rock Volume geometry and prediction of its evolution during gas or oil production. Total E&P has implemented recently an experimental set-up allowing creating shear fracture on a cylindrical plug of shale rock in a conventional triaxial and measuring permeability tests to water and to gas according a specific protocol simulating the change of in situ effective stress and pressure gradient in the near and far field of perforation. After creating shear fracture, we filled the fracture with proppants used in frac job, and we performed measurements of permeability to gas under various effective stress condition. The hydraulic aperture of fracture with different concentration of proppants is then determined.
When the fracture is filled with proppants, significant decrease (−20%) of the fracture hydraulic opening is clearly observed when confining pressure increases from 10 to 300 bars for the fracture filled with 1 layer of 30/50 mesh ceramic proppants. Compared to the fracture without proppants, the relative decrease of hydraulic opening (e/e0) is 5 times less for fracture with one layer of proppants. When the fracture was filled with 2 layers of same proppants, the amplitude of change of fracture opening is 3 times less compared to that with one layer of proppants. Embedment of proppants on fracture surface is observed. The fracture filled with natural sand is much more sensitive to confining pressure compared to the fracture filled with ceramic proppants 30/50 mesh.
We present in this paper the protocol, the calibration of the experimental set-up and the main results of fracture permeability to water and to gas obtained on a Vaca Muerta shale sample, filled with different quantities of proppants.
The potential of gas production is first and foremost determined by geochemical and petrophysical factors such as total organic carbon content, thermal maturity, porosity and permeability. However, the productivity is strongly dependent on the fracture network connectivity and permeability since the shale matrix has extremely low permeability, and acts as a seal to many conventional reservoirs. Many geomechanical parameters of shale control the hydraulic quality of stimulated reservoir volume (SRV) created by hydraulic fracturing.
