Permeability Measurement of Organic-Rich Shale - Comparison of Various Unsteady-State Methods

Abstract

Accurate determination of organic-rich shale permeability is still a major challenge. Various methods have been proposed to measure the permeability on core plugs or crushed samples under various stress conditions using different fluids. Permeability obtained from core plugs and their crushed samples could differ by two orders of magnitude, potentially painting very different views of the reservoirs and resulting in differences in asset development workflows. This situation only reinforces the need for considerable additional focused work to quantify tight rock permeability and better understand the measurement method dependence. This paper presents the experimental comparison of three different unsteady-state transient methods for measuring the permeability of organic-rich shale plugs: pressure build-up, pulse-decay and oscillating pulse techniques. Permeability measurements are conducted isothermally using nitrogen gas on core plugs from the Barnett, Eagle Ford, Marcellus and Mancos formations at the same confining pressure and pore pressure. These plugs differ in mineralogy, total organic carbon (TOC), nuclear magnetic resonance (NMR) and helium porosity. Fractures are observed through the horizontal samples along the gas flow direction, while vertical samples do not have fractures. For each plug, the permeability tests begin with the pressure build-up measurement, and are followed sequentially by the pulse-decay and oscillating pulse methods whenever applicable. The plugs are then cut into smaller sizes for continuation of permeability tests and investigation of the permeability dependence on the plug size. For the samples analyzed, the permeability measured from the pulse-decay method is essentially identical to that from the oscillating pulse method. Compared to these two methods, the pressure build­up test generally gives a relatively higher value when requiring an independent porosity measurement to compute the permeability, while it gives a relatively lower value when no porosity is needed. However, the permeability difference among these methods is generally small. This indicates that the pressure build-up test can be used to perform permeability measurement on large core plugs that cannot be tested using the pulse-decay or oscillating pulse methods. There is no trend observed on the permeability dependence on the plug sizes used. Depending on fracture distribution and connectivity, the measured permeability of horizontal samples is randomly affected by the sample sizes, indicating multiple samples with various sizes may be required to obtain a representative permeability value for horizontal plugs. Vertical plugs show little permeability dependence on the sample sizes. Consequently, a small vertical plug can be used for very tight rocks enabling quicker matrix permeability measurements.

Experimental Investigation on Permeability and Porosity Hysteresis in Low-Permeability Formations

“…Transient permeability measurement approach can be performed on crashed cores, commonly known as Gas Research Institute (GRI) method (Luffel et al, 1993;API 1998;Cui et al, 2009;Passey et al, 2010;Profice et al, 2012;Tinni et al, 2012;Heller, et al, 2014;Civan and Devegowda, 2014), or on intact cores Lin, 1977;Haskett et al, 1988;Dicker and Smith 1988;Jones 1997;Akkutlu and Fathi, 2012;Mokhtari and Tutuncu, 2015;Jin et al, 2015;Zhou et al, 2016). Unsteady state (transient) methods are the alternatives to measure micro and nano-Darcy permeability formations at a reasonably short time.…”

From Mineral Surfaces and Coreflood Experiments to Reservoir Implementations: Comprehensive Review of Low-Salinity Water Flooding (LSWF)

“…In both cases, the ζ potential measurements have shown to be dependent on cation type. Also, it may be logical for ζ potential measurements on solid and crushed samples to differ because both states exhibit different permeabilities, but this is of less importance because the focus is on surface chemistry and not flow transmissibility. Nonetheless, ζ potential measurement is effective in studying COBR systems: reflecting multiple surface properties, examining the influence of pH and ionic strength, , examining the presence of specific functional groups, and investigating the adsorption and desorption behavior of crude oil components on rock surfaces.…”

Gas permeability measurements from pressure pulse decay laboratory data using pseudo-pressure and pseudo-time transformations

“…Third, pore pressure oscillations method was proposed in order to tackle the problem of getting noisy signal from the pulse decay technique. In this method, sinusoidal pore pressure pulse is sent from the upstream of the sample and based on the retardation of the signal and phase change at the downstream, permeability can be calculated (Fischer 1992;Jin et al 2015). However, recent pressure transducers do not cause noisy signals that require a new modification on enhancing the signal, especially when the signal is clear from a simpler measurement technique like the pulse decay.…”