Petrological Analysis (1)-- Applications for Reservoir Geology

S ummary
The mineralogical and chemical compositions and pore characteristics of reservoir rocks exert fundamental controls over a petroleum system. The
application of petrological analytical techniques to reservoir geology has proved so fruitful that modern petroleum and geothermal geology cannot be
conducted effectively without it. The JAPEX Research Center has successfully employed a variety of petrological techniques in petroleum andgeothermal exploration.

XRD (X-ray Powder Diffraction)

Resin-Impregnated Thin Sections

0.5 mmX ray diffraction goniometerThin section observation is an important first step that should be carriedout in petrological analysis. Lithofacies, the progression of diagenesis andthe development of porosity can be identified through these observations.
At our research center, blue resin-impregnated thin sections are preparedto more easily identify pores.

X-ray diffraction (XRD) analysis is a basic technique for mineral
identification. The diffraction peak specific to a mineral present isgenerated when a fixed powdery sample is irradiated with X-rays. The
mineral composition and crystal structures are analyzed based on theresulting data. The diagenesis and hydrothermal alteration of the rockare thus evaluated.

XRF (X-ray Fluorescence Spectrometry)

Scanning Electron Microscopy with EDS

X-ray fluorescence (XRF) analysis is a method used to analyze a constituent
element and the amount of that element in the material based on thefluorescent X-ray energy generated, and its strength, when a sample isirradiated with X-rays. The emitted fluorescent X-rays are characteristic
for each element, and the strength of those characteristic X-rays is related
to the quantity of the corresponding element in the sample. Furthermore,
the ability of X-rays to penetrate a material is high, and this method issuitable for nondestructively analyzing solid, liquid and powder samples.

Fluid Inclusion Microthermometry

Scanning electron microscopy enables observation of the shape of aVDPSOH·V surface by squeezing an electron beam and scanning theVDPSOH·V surface and detecting secondary electrons and backscatteredelectrons emitted by the surface. In addition, we can perform thechemical analysis based on characteristic X-ray emission withsecondary and backscattered electrons and attached energy dispersive
X-ray spectrometry (EDS).

Cathode Luminescence Analysis

Number means homogenization temperature (Th, deg.C)

Fluid inclusion is a generic name for liquid and gas taken up inside amineral; these inclusions can be used to estimate the physicochemical
conditions under which they were trapped within the mineral. The
homogenization temperature (Th) and ice melting temperature (Tm)
are checked at times of heating and cooling under a microscope. The
temperature and salinity (NaCl wt% equivalent) when a fluid was taken
up are thus estimated.

The cathodoluminescence (CL) technique involves detecting the lightreleased when a sample is irradiated with an electron beam. This
WHFKQLTXHLVXVHGIRUDQDO\VLVRIDVDPSOH·VFU\VWDOVWUXFWXUHYHU\small amounts of impurities, lattice defects and crystal distortions.
The range applications of this method in geology is wide; examples
include the stage division of authigenic minerals and tectonic stressanalysis.

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Petrological Analysis (2)-- Applications for Reservoir Geology

Carbon and Oxygen Stable Isotope Analysis

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CO2 gas from reactions between carbonates and phosphoric acid ismeasured. The isotopic ratios of carbon ĵ13C) and oxygen ĵ18O) vary
between depositional/diagenetic environments.
 ĵ18O ‫؟‬water temperature and salinity of the formation fluid ĵ13C ‫؟‬mixing of carbon sources (biogenic/thermogenic/volcanic)

Grain size distribution analysis includes various technique, but thesieve method is used here because of the number of samples that canbe analyzed and the wide range of adaptations to grain fabric ofsandstone reservoir available. The results of this analysis areexpressed as an accumulation frequency curve or weight histogram, andmay require calculations of sorting, skewness and kurtosis. These data
are used in evaluation of the depositional environment.

Thermal Conductivity Measurement

Magnetic Susceptibility Measurement

Thermal conductivity is an index used to evaluate heat movement
phenomena according to )RXULHU·V law. For an object close to two heatsources with the different temperatures, a temperature incline reaches asteady state (flat) within several minutes. The constant Ǉ here called thethermal conductivity, by the heat capacity (quantity of heat flux) to flowat this time in proportion to a temperature incline is shown in expression(1).
J = -ǇgradT - - - (1)What Can Petrological Analysis Tell Us ?

RevisedWaples (1980) andTissot and Welte (1984)

In the exploration and evaluation of oil, gas and geothermal resources,
petrological and mineralogical analyses are essential to understandreservoir rock properties. These properties vary in terms of grain size,
sorting, burial depth, lithofacies and rock type. In addition, althoughinitial interparticle porosity is important, the property of porosity
change considerably through diagenesis and/or hydrothermal alteration.
For carbonate rocks, reservoir rock properties are particularlytransformed by diagenesis. These conclusions are based on petrologicalanalysis.

Magnetic susceptibility refers to magnetization, which indicates thestrength of the magnetic field. This value depends on whether therock includes magnetic minerals such as the magnetite. This value
can be used for identification and comparison of the rock, and as anindex of the degree of hydrothermal alteration.

Key Points
The JAPEX Research Center conducts the following petrologicalanalyses to explore and evaluate oil and gas reservoirs andgeothermal fields:(1) Resin-impregnated thin sectioning and observation(2) XRD (X-ray powder diffraction)(3) XRF (X-ray fluorescence spectrometry)(4) Scanning electron microscopy with EDS(5) Fluid inclusion microthermometry(6) Cathodoluminescence analysis(7) Carbon and oxygen stable isotope analysis(8) Grain size distribution analysis(9) Thermal conductivity analysis(10) Magnetic susceptibility analysis
The most frequently applied analyses are resin-impregnated thinsectioning and observation, XRD, XRF, and fluid inclusion
microthermometry. Pore size distribution measurements are also
important for evaluating the pore systems in a rock.
We hope that you will find this brochure useful, particularly theabove key points. We look forward to your feedback and futurecooperation.

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