Measurement of the Marcellus Shale Properties

Abstract

Abstract Even though the advances in horizontal drilling and hydraulic fracturing techniques have unlocked the gas contained in Marcellus shale, the quantification of the petrophysical properties remain challenging due to complex nature of the shale. Shale permeability is commonly measured by the unsteady state methods, such as pulse-decay or GRI methods, because the shale has a permeability in nano-Darcy range. The permeability values by determined by these techniques have been found often to have large margin of uncertainty as a result of inconsistent experimental protocols and the complex interpretations methods. In this study, petrophysical properties of the Marcellus shale core plugs were measured using an innovative laboratory setup, referred to as Precision Petrophysical Analysis Laboratory (PPAL). PPAL is designed to accurately measure the petrophysical properties of ultra-low permeability core plugs under the reservoir conditions. PPAL measurements are performed under steady-state isothermal conditions flow conditions and the analysis of the results do not require complicated interpretations. The key advantage of the PPAL is the capability to measure the permeability and porosity of the shale core plugs under a wide range of confining and pore pressures. In addition, the impact of gas adsorption (or desorption) on the measurements can be monitored. The core plugs used in this study were made available through the Marcellus Shale Energy and Environment Laboratory (MSEEL), a dedicated field laboratory in the Marcellus Shale. MSEEL has been established to undertake field and laboratory research to advance and demonstrate new subsurface technologies and to enable surface environmental studies related to unconventional energy development. The filed site is owned and operated by Northeast Natural Energy, LLC and contains several horizontal Marcellus Shale wells. In addition, a vertical well has been drilled specifically for obtaining core, log, and other data for scientific purposes (science well). The results of the core plug permeability measurements indicated that that the permeability values decline as the gas (pore) pressure increases. Reliable values of the absolute permeability can be obtained by the application of the double-slippage correction for all pore pressure ranges but more specifically for pore pressures below 900 psia. Klinkenberg correction on the other hand, can only provide reliable values for the absolute permeability when the pore pressures are above 900 psia. The determined absolute permeability values were found to be impacted by the net stress. The analysis stress data with the aid of Walsh plot provided the estimates of the fracture (fissure) closure pressure. The closure pressure was found to be dependent on the absolute permeability.