A method of proppant pack permeability assessment

Hydraulic fracturing methods used for low permeability reservoirs such as shale gas or tight gas require the use of proppants. The current standard used for proppant assessment does not take into account its interaction with the rock and the embedment effect. In this paper a new method of proppant pack permeability assessment is proposed where proppant is placed into a rock sample with induced fracture. Three types of proppant were assessed to verify the method i.e. offshore sand, onshore sand and ceramic proppant. The rock sample was a Tumlin sandstone. As the flowing medium supercritical carbon dioxide was used. Tests were performed with 300-500 μm size proppants at flowing pressure of 3 MPa and confining pressure of 5 MPa. Additional test was conducted with 1–2 mm sand proppant at two confining pressure, i.e. 5 MPa and 16 MPa. Proppant were characterized in accordance with the Krumbein/Sloss diagram. Similar values of permeability for the proppant concentration of 0.5 kg/m2 were obtained ranging from 2.3 to 3.3 D although the highest permeability was achieved with Baltic sand proppant and ceramic proppant. For the larger size of proppant (1 – 2 mm) the initial permeability with confining pressure of 5 MPa was initially larger but when the confining pressure was increased it declined by 37%. This proves that in the proposed method we can observe changes in the permeability of the fracture with change in confining pressure apply subjected to the sample.