Measuring anisotropic permeability using a cubic shale sample in a triaxial cell

• A new experimental setup for anisotropic permeability measurement in triaxial rigs.
• Cubic rock sample with 3D printing membrane to simulate a standard core sample.
• The Silurian longmaxi shale sample has a vertical and horizontal permeability ratio of 0.04.
• Reservoir simulation indicates anisotropic permeability should be measured and used for gas production prediction.

Reservoir rocks for water, oil and natural gas, as well as for CO2 storage are often anisotropic in permeability, due to different pore or layering structures in different directions. Therefore, anisotropic permeability is an important parameter to measure when analysing fluid flow performance in reservoirs. Permeability is commonly measured using a triaxial cell, and anisotropic permeability is often traditionally measured using subcored cylindrical samples from a recovered core. However, the sample's heterogeneity can significantly affect the test results. Cubic samples can eliminate the effect of heterogeneity when measuring anisotropic permeability, but sealing is a major challenge that limits the use of this technique. In this work, a 3D-printed membrane was made to hold cubic shale sample. The cubic sample and 3D-printed membrane assembly which simulate a normal cylindrical core was then installed in a rubber sleeve for permeability measurement in a triaxial cell. Re-orienting the sample in the triaxial cell enabled permeability measurements along each directional axis. Using helium gas to demonstrate the technique, our results show that the shale sample taken from the Longmaxi Formation in Sichuan Basin, China has strong permeability anisotropy, with permeability perpendicular to bedding about 4% of that parallel to bedding. Through reservoir simulation using different permeabilities, we demonstrate that anisotropic permeability has a large impact on modelling gas production, suggesting that anisotropic permeability should be routinely measured and applied to the modelling of fluid flow in reservoir rocks with high permeability anisotropy, such as shales. Our measurement technique can be readily applied to any existing triaxial rigs and will benefit future reservoir evaluation and characterisation.