The exceedingly fine-grained and fracture-prone nature of shale/mudrock reservoir core challenges efficient provision
of fundamental core data sets that include porosity, permeability, grain density, and core saturations. To do
so typically requires special sampling, analytical, and measurement techniques. Core Laboratories worked with
investigators representing the Gas Research Institute in development of the core analysis method referred to as
"GRI" (GRI final report: GRI-95/0496). The method involves determination of intact-sample as-received bulk density.
Then, by reducing the sample to a quantity of small particles, 0.5 to 0.85mm diameter, coring- and sampling-induced
fractures are eliminated and pore pathways are greatly shortened so that efficient processing for pore liquid
removal and quantification by distillation-extraction can be accomplished. Subsequent dry grain volume determinations
conclude the sequence providing porosity, grain density, and core saturations.
GRI-method permeability is an unsteady state gas pressure-decay technique and may be determined using particles
containing as-received pore liquids, yielding an effective kg or using clean-dry particles, yielding an absolute
kg. In some cases, both permeabilities are determined. The effects of coring- or sampling-induced fractures
and cracks are eliminated by use of small-particle samples and because of this the results are often referred
to as matrix permeability or km.
GRI "crushed" core analysis method provides:
Particles in the 20-35 US mesh size range (0.85 to 0.5mm), above, are used in the GRI core analysis method. In
typical shale or mudrock, each particle will contain many thousands of individual grains and the associated pore
bodies and pore throats.
Core Laboratories has developed the SMP-200, a new, built-for-purpose, particle permeameter. It incorporates
a modified helium pycnometer and proprietary algorithms for derivation of km from sample parameters and test data.