CORE ANALYSIS BASICS
This page is an overview of most of the laboratory procedures available to describe rock samples taken from wellbores. More detailed descriptions of the techniques are presented in other Section sof this Chapter -- see links at the right.

CONVENTIONAL CORE ANALYSIS
Routine, or conventional,  core analysis provides geologists and engineers with "hard data" related to the downhole environment. Generally considered to be the "ground truth", Conventional core data is used to calibrate log analysis results, reservoir simulations, and stratigraphic correlations.

Core Plugging and Slabbing
Core sample physical properties are usually determined from 1.5" diameter plug samples cut from bulk subsurface core. For whole-core analysis, the cylindrical core material is cut lengthwise into two slabs using a specially designed saw. The slabbed cores can be displayed for description, viewing, or documentation.

Core Gamma Ray
A spectral gamma ray log of the core is essential for depth control to well logs. It is helpful in understanding radioactive sands and carbonate reservoirs.

Basic Properties
Basic properties are measured on cleaned, dry samples drilled from the whole core by diamond bit core drills. Standard basic property measurements are helium porosity and permeability (Klinkenberg corrected), grain and bulk density, residual oil and water saturation, and visual lithology descriptions.

Sidewall Core Analysis
Analysis of both rotary and percussion sidewall cores include bulk volume, porosity, fluid content, laser grain size analysis, air permeability (empirical estimate), and photography (colour and UV).

Core Photography Digital Imagery provides an easily accessible visual record of a core, core plugs, well cuttings, and thin sections. Imagery is digitized at either microscopic or near-microscopic resolution. It also serves as a source of petrologic and petrophysical data. Under ultra-violet light, oil fluoresces, so photos in both natural and UV light need to be taken.

X-Ray Computed Tomography (CT) ANALYSIS
X-ray computed tomography is now the industry-wide technology for whole-core inspection at the macro level, core-log correlation, and plug sample characterization. Standard output includes CT radiograph plus axial CT scans. Plug scans may also include both longitudinal and axial CT scans.

X-Ray CT Scan Images

Digital Rock Physics from Macro, Micro, and Nano CT Analysis
Digital Rock Physics is a term used to describe more detailed analysis of CT Scan images. First, higher resolution images than conventional CT scans are made. Then the pore size and shape are quantified in three dimensional space, and a series of well defined equations are used to generate computed rock properties, such as porosity, permeability, capillary pressure, relative permeability, electrical properties, mineralogy, elastic properties, and so on. Some of these can be defined in the three primary directions (X, Y, and Z directions). Total, effective, connected, unconnected, and fracture porosity can be derived. Permeability as low as a few nanoDarcies can be detected. Samples can be taken from cores, core plugs, or drill cuttings. The latter allows measurement of quantitative rock properties without coring - a significant cost saving on current wells and an invaluable source of new information on older wells.

Digital Rock Physics

The list above shows the breadth of quantitative data that can be developed from digital rock physics CT scans. Considerable super-computer power is required to manipulate the 3-D data set through the numerous heavy-duty equations. One day, the technique will be turned inside-out, as was done for the NMR method, and micro CT scans will become a borehole well log. In the meantime, grap your sample chips and start re-logging those critical unconventional reservoirs..

Macro Level Properties =

Micro Level Properties

Nano Level Properties in Shale
White = Porosity

X- Ray Fluoroscopy
High-resolution fluoroscopy provides the ability to perform quantitative image analysis, including a high resolution density log of the entire core. Each scan contains X-Ray density standards. The log provides an important record of variations in lithology and porosity throughout the length of the core. This provides approximate porosity and lithology estimates before the core is even slabbed.

SPECIAL CORE ANALYSIS MEASUREMENTS
Special Core Analysis (SCAL) provides specific information to characterize a particular rock property, or through a selection of specialized tests, provides a more complete understanding of a reservoir rock. 

Capillary Pressure
Capillary pressure measurements are available using porous plate, high-speed centrifuge, or mercury injection techniques. Porous plate measurements can be performed at ambient and/or elevated temperatures. Centrifuge data is currently limited to ambient or moderate temperatures. PTS is equipped with 2 automated Micromeritics mercury injection porosimeters for testing at pressures up to 60,000 psi.

Relative Permeability
We encourage early consultation with our clients in an effort to design relative permeability test programs that are consistent with processes in the field. PTS offers a full complement of relative permeability tests including:

Wettability Testing
Knowledge of the wettability of a reservoir rock is a key factor for determining oil recovery mechanisms and making estimates of recovery efficiency. PTS offers industry-standard Amott and Modified USBM wettability tests, including the USBM test at elevated temperatures. For samples that have been subjected to weathering, PTS offers sample restoration in crude oil at reservoir temperature.

Pore Volume Compressibility
Hydrostatic pore volume compressibility testing is a routine offering for 1-in., 1.5-in. and 2-in. diameter samples and pressures up to 10,000 psi. Cyclic compression and decompression tests, as well as failure point determination tests, are also available. PTS has in-house capabilities to perform uniaxial or triaxial stress testing. Advanced geomechanical determinations are also available.

NMR Analysis
PTS Labs is equipped with a state-of-the-art Maran Ultra NMR core analyzer, and flow-through core holders capable of testing at both ambient and reservoir conditions. For calibration with downhole logging tools, the instrument can match pulsed NMR tool magnetic strength and T2 echo spacing. NMR determinations include:

PETROGRAPHIC ANALYSIS
Petrographical analyses is an essential service providing estimates of pore size distribution, grain size, sorting, porosity and mineral abundances, fabric, rock classification, porosity varieties and abundances.

Thin Section Petrography Detailed thin section analysis includes measurement of mean grain size, sorting, and point count determination of mineral abundances and porosity (minimum 300 points per thin section). Results include a determination of Vshale, shale distribution, porosity varieties and abundances with a discussion of diagenesis, diagenetic sequence, porosity origins and development, controls on porosity and permeability. Point count data is presented in tabular form with color photomicrographs accompanied by detailed descriptions. X-Ray Diffraction Analysis XRD analysis provides semi-quantitative determination of sample mineralogy. Bulk and clay X-ray diffraction analysis is performed to aide in reservoir description and evaluation of reservoir diagenesis. The data provided in tabular format. Scanning Electron Microscopy Analysis The data output includes two (2) photographs at varying magnification documenting significant rock properties, pores, pore throats, clays, framework grains and cements. Deliverables include a complete written description, and elemental abundance from EDS analysis. Back-scatter SEM allows for the development of petrophysical properties on cutting and percussion sidewall cores where other measurements cannot be accurately made. Analysis requires BSI on ultra polished billet and SEM photomicrograph on fresh surface. Data results are presented in both tabular and graphical formats and includes: Porosity Porosity distribution (percent primary intergranular and micro porosity) Permeability Pore size distribution Mean pore body diameter (ferret diameter) Mean pore throat diameter Mean aspect ratio Average coordination number Pore shape factor Capillary pressure curves Formation factor ("m") T-2 distribution plot