New Experimental Approach to Measure Petrophysical Properties of Organic-Rich Shales

Production from hydrocarbon reservoirs is strongly dependent on the permeability of the formation. For decades, the permeability of conventional reservoirs, which are typically in milli-Darcy range, has been measured by the steady-state laboratory technique which provides accurate and fast results. In contrast, unsteady state techniques such as GRI or pulse decay have been used to measure the permeability of unconventional formations such as shales due to their ultra-low permeability. GRI technique is carried on crushed samples and is considered a fast technique for matrix permeability measurement. However, recent studies have found that reported GRI measurements results by different commercial laboratories are often inconsistent. This may be related to the sample crushing method. Moreover, GRI technique cannot measure the permeability of the sample under reservoir stress conditions. Pulse decay is a different technique for measuring permeability of the core plugs. Pulse decay measurement results are also found often to be inconsistent.;This study introduces a new, fast and robust technique for measurement of the shale core plug sample permeability under steady-state condition. A laboratory set-up has been designed and assembled which has a resolution of one millionth standard cubic centimeters per second for gas flow rate and one hundredth cubic centimeters for pore volume measurement. This resolution allows permeability measurements in nano-Darcy range. Extremely accurate differential transducers are used to measure the pressure drop as gas flows through the core plugs under confining pressure. The application of confining pressure and maintaining isothermal conditions allows replication of the in-situ conditions. The laboratory set-up is fully automated to eliminate any human error and more importantly to maintain the temperature stable within the enclosed unit. The permeability can be measured under wide range of pore and confining pressures. Gas slippage corrections can be applied to the results to evaluate the absolute permeability. When adsorbate gases such as CO2 and CH4 are used in this laboratory setup, the measurements can provide the permeability hysteresis due to adsorption or desorption. Moreover, the ability to test the sample under different stress conditions can be used for the matrix-fracture characterization of the shale sample. Finally, the experimental results can be interpreted for sorption and pore size characterization