PLUNGING ANTICLINE IN THE KIMMERIDGE CLAY : Multibeam bathymetry image

Relationship of shale pore diameters to the molecular diameters of petroleum, with increasing depth of burial. At moderate depths of burial, shale pore diameters typically

become very small in relation to the larger petroleum molecules such as the asphaltenes.

• Micelles : molecules behaveing like soap, attach to a hydrocarbon molecule on one end and to an OH- at the other end.

• Can increase the amount of hydrocarbons transported by water.

• However, micelles are not found in rocks in sufficiently large quantities to explain most hydrocarbon accumulations.

A picture is worth a thousand words

Plane polarized transmitted light photomicrograph

Fluorescent microscopy showing well-connected horizontal microfracture network with submicroporous porosity

Bubble point line

Dew point line

Bulk volume of the cell Vbulk = L3

Number of spheres in the cell

n =(L/2r)3

Volume of the matrix Vmatrix = (4nπ r3)/3 = (L/2r)3 (4πr3)/3

= (π L3)/6 Porosity

DUAL POROSITY IN SANDSTONE

MATRIX

FRAMEWORK (QUARTZ)

FRAMEWORK (FELDSPAR)

CEMENT

PORE

Note different use of “matrix” by geologists and engineers

0.25 mm

Sandstone Comp. • Framework • Matrix • Cement • Pores

DISSOLUTION PORE

FRACTURE

1. Primary and secondary “matrix” porosity system 2. Fracture porosity system

SANDSTONE COMPOSITION, Framework Grains

Norphlet Sandstone, Offshore Alabama, USA Grains ~0.25 mm in Diameter/Length

PRF KF

P

KF = Potassium Feldspar PRF = Plutonic Rock Fragment

P = Pore Potassium Feldspar is Stained Yellow With a Chemical Dye

Pores are Impregnated With Blue-Dyed Epoxy

Q

Q = Quartz

Photo by R. Kugler

SECONDARY POROSITY: INTRAGRANULAR INEFFECTIVE

Scanning Electron Micrograph Tordillo Formation, Neuquen Basin, Argentina

Partially Dissolved Feldspar

Dissolution Pores may be Isolated and not contribute to the effective pore system

POROSITY IN SANDSTONE

Quartz Grain

Pore

Scanning Electron Micrograph Norphlet Sandstone, Offshore Alabama, USA

Porosity in Sandstone Typically is Lower Than That of Idealized Packed Spheres Owing to:

Variation in Grain Size Variation in Grain Shape Cementation Mechanical and Chemical Compaction

Photomicrograph by R.L. Kugler

POROSITY IN SANDSTONE

Scanning Electron Micrograph Tordillo Sandstone, Neuquen Basin, Argentina

Pore Throats in Sandstone May Be Lined With A Variety of Cement Minerals That Affect Petrophysical Properties

Photomicrograph by R.L. Kugler

POROSITY IN SANDSTONE

Scanning Electron Micrograph Norphlet Formation, Offshore Alabama, USA

Pores Provide the Volume to Store Hydrocarbons Pore Throats Restrict Flow through pores

Pore Throat

Secondary Electron Micrograph

Clay Minerals in Sandstone Reservoirs, Authigenic Chlorite

Jurassic Norphlet Sandstone Offshore Alabama, USA (Photograph by R.L. Kugler)

Occurs as Thin Coats on Detrital Grain Surfaces

Occurs in Several Deeply Buried Sandstones With High Reservoir Quality

Iron-Rich Varieties React With Acid

~ 10 µ m

Electron Photomicrograph

Clay Minerals in Sandstone Reservoirs, Fibrous Authigenic Illite

Jurassic Norphlet Sandstone Hatters Pond Field, Alabama, USA (Photograph by R.L. Kugler)

Illite

Significant Permeability Reduction

Negligible Porosity Reduction

Migration of Fines Problem

High Irreducible Water Saturation

INTERGRANULAR PORE AND MICROPOROSITY

Intergranular Pore

Microporosity

Kaolinite Quartz Detrital Grain

Intergranular Pores Contain Hydrocarbon Fluids

Micropores Contain Irreducible Water

Backscattered Electron Micrograph Carter Sandstone, Black Warrior Basin, Alabama, USA (Photograph by R.L. Kugler)

Clay Minerals in Sandstone Reservoirs, Authigenic Kaolinite

Secondary Electron Micrograph

Carter Sandstone North Blowhorn Creek Oil Unit Black Warrior Basin, Alabama, USA

Significant Permeability Reduction

High Irreducible Water Saturation

Migration of Fines Problem

(Photograph by R.L. Kugler)

PORE-SPACE CLASSIFICATION • Total porosity, φt =

• Effective porosity, φe =

VolumeBulkPore VolumeTotal

VolumeBulkPore SpacectedInterconne

• Effective porosity – of great importance;

contains the mobile fluid

COMPARISON OF TOTAL AND EFFECTIVE POROSITIES

• Very clean sandstones : φe → φt

• Poorly to moderately well -cemented intergranular materials: φt ≈ φe

• Highly cemented materials and most carbonates: φe < φt

Quartz(Framework) SmallPores IsolatedPoresLarge, InterconnectedPoresClay Surfaces& InterlayersClayLayers

Irreducible orImmobile WaterHydration orBound Water HydrocarbonPore VolumeStructural(OH ) Water

RockMatrix

Total Porosity - Neutron LogTotal Porosity - Density LogAbsolute or Total PorosityOven-Dried Core Analysis PorosityHumidity-DriedCore Analysis PorosityCapillaryWater

VShale

Sandstone Porosity Measuredby Various Techniques

(modified from Eslinger and Pevear, 1988)

Quartz(Framework) SmallPores IsolatedPoresLarge, InterconnectedPoresClay Surfaces& InterlayersClayLayers

Irreducible orImmobile WaterHydration orBound Water HydrocarbonPore VolumeStructural(OH ) Water

RockMatrix

Total Porosity - Neutron LogTotal Porosity - Density LogAbsolute or Total PorosityOven-Dried Core Analysis PorosityHumidity-DriedCore Analysis PorosityCapillaryWater

VShale

Sandstone Porosity Measuredby Various Techniques

(modified from Eslinger and Pevear, 1988)

SANDSTONE POROSITY MEASURED BY VARIOUS TECHNIQUES

Quartz (Framework)

Small Pores

Isolated Pores

Large, Interconnected Pores

Clay Surfaces & Interlayers

Clay Layers

Irreducible or Immobile Water

Hydration or Bound Water

Hydrocarbon Pore Volume

Structural (OH - ) Water

Rock Matrix

Total Porosity - Neutron Log Total Porosity - Density Log

Absolute or Total Porosity

Oven-Dried Core Analysis Porosity Humidity-Dried

Core Analysis Porosity

Capillary Water

V Shale

(modified from Eslinger and Pevear, 1988)

Carbonate porosity

Crystalline dolomite m = 1.95, φ = 47%, k = 3160 mD

Terrible uncertainty

K also Inverse of τ : Tortuosity (Total length/Mean path length)2

SV : Specific Surface Are (Area/ Rock volume)

Typical Specific Surface Areas

Material SV (cm-1)

Sand 80

Kaolinite (clay) 500

Smectite (clay) 1300

Illite (clay) 2800

Fundamental of CK eqn.:

Increased Surface area causes

increased flow resistance & Flow

Seperataion

• Permeability correlates inversely with

the clay content of sands.

• Sand > 35% clay Not Productive to oil

• Gamma ray log as good indicator of k

Reservoir Sandstone in 2-D Navajo Sandstone, porosity 13%, permeability ~200 mD

Real Rocks Are Three-Dimensional Pathways in 3-D are different from 2-D !

Pore Network of a Sandstone in 3-D Synchrotron tomography of sandstone.

Volume is one cubic millimeter and resolution 1 micrometer

Major Factors Affecting k

Typical occurrences of clay minerals in sandstones

Plot of decimal fraction of illite in I/S from shales in a typical well.

Individual points are sample measurements

The line is calculated from a burial history

Thermal history schematic showing integration of paleothermometers

Illite data constrain the burial or heating phase of a basin’s thermal history,

%R records maximum temperature, and apatite fission track analysis constrains timing of uplift and cooling

Illite and hydrocarbon exploration DAVID R. PEVEAR, Exxon Production Research, Proc. Natl. Acad. Sci. USA Vol. 96, pp. 3440–3446, March 1999

Laser fluorination is a specialised technique utilising a custom online preparation, extraction and purification system for the extraction of oxygen from silicate, oxide and clay minerals.

The technique is essential to release oxygen from these minerals and requires samples to be combusted in an atmosphere of either BrF5, ClF3 or F2

Zach Sharp all stainless steel line utilising BrF5 (Image courtesy of Dr. Zach Sharp)

Zach Sharp modified stainless steel and glass line utilising ClF3 (Image courtesy of Dr. Craig Barrie)

3-D Reservoir Architecture

Reservoir Connectivity

3-D Reservoir Shapes Map showing the initial production of wells in an oil Field. The contours follow almost precisely the isopach map of the net reservoir sands. What is the nature of this Reservoir: Way to avoid the dry wells (single dots outside the contoured areas)

F

γ Ө

r R

h Water

Oil

F = Upward force along contact γ = Surface tension cos Ө = F/γ Grav./Bouyancy force Total F = 2πr. γcos Ө = πr2 hρg Capillary force h= 2γcos Ө /rρg ρw – ρo Important

calcite

Quartz

University of Georgia Department of Geology GEOL 4320 Petroleum Geology

Shepherd 2009

σ1>σ2>σ3