AFES Seminar

“Basic FormationEvaluation –

So what’s so Special aboutCore Analysis?”

Presented byRichard Arnold

CORE LABORATORIES (U.K.) LIMITED

AFES Seminar

•Cores are the only representative element ofthe reservoir rock that are physicallyavailable for examination and modelling forbasic flow processes.

•Special Core Analysis reduces uncertaintyand reduces risk

Why Core Analysis?

AFES Seminar

Why Core Analysis?

• Reservoir Geological Model –defines volumetrics• Total hydrocarbons in place (= total assets)

• Productivity Index (= cash flow)

• Recovery, STOIP - STOresidual (= bankable assets)

t

n

o

b

hh

BSwV

STOIP .)1.(.

noo

hB

KPI .

.

AFES Seminar

Where? - Data Sources

SEISMIC &GEOLOGICAL DATA

Reservoir StorageCapacity

Fluid SaturationsHydrocarbons in place

Fluid Flow

FIELD DATALABORATORY

DATA

Reservoir Engineering Model

Hydrocarbon Recovery Predictions

PorosityCompressibility

Capillary PressureResistivities

Single & MultiphasePermeabilities, PVT

Porosity Tools

Resistivity Tools

Well Flow Tests

AFES Seminar

How?- Methods

CORING PROCESS

CORE

ROUTINE

Porosity, Permeability,Log, Grain Density,

Fluid Saturations

OVERBURDEN

ADVANCED

Air/BrineAir/Mercury

Oil/Brine

FRF m + aRI n

Shale effects

CompressibilityPermeability

Rock Mechanics

RelativePermeability

CAPILLARY PRESS. ELECTRICAL WETTABILITY FLUID FLOW

SinglePhase

FormationDamage,

Stimulation

Gas/Oil/BrineDrainage/Imbibition

Unsteady/Steady StateRoom/Reservoir Conditions

GEOLOGICAL

Core DescriptionThin Section, XRD, SEM

AFES Seminar

Sample Preparation

•How do we select representative samples?•How do we prepare suitable samples for

testing?

AFES Seminar

CT Images

Preserved Whole Sample Plug Sample

AFES Seminar

Directional Plugging

BeddingPlane

Direction

‘Horizontal’Plug

Unsuitable Plug

‘Vertical’Plug

AFES Seminar

Petrographic Analysis

AFES Seminar

Clay Minerals

General clay effects on petrophysical properties:

• Reduce permeability and porosity

• Increased retention of water–Microporosity –capillary bound water; localized or

continuous–Water of Hydration –“Clay Bound Water”(CBW)

• Suppression of resistivity

• Over-estimation of porosity by Neutron log

• Increased potential to reduce productivity–Pore plugging by fines migration and/or swelling

AFES Seminar

Clay Types

Main clay types:

KaoliniteKaolinite

ChloriteChlorite

IlliteIllite

SmectiteSmectite

Mixed layerMixed layer

AFES Seminar

Kaolinite

• Non-expanding• Low cation exchange

capacity• Platelets or booklets

• May migrate

AluminaAlumina

SilicaSilica

7.27.2 ÅÅ

AFES Seminar

Chlorite

• Non-expanding• Low cation exchange capacity• Platelets or honeycomb

aggregates• May migrate• Contact with HCl Acid releases

iron (Ferric Hydroxide)

AluminaAlumina

SilicaSilica

SometimesSometimesIronIron

1414 ÅÅ

AFES Seminar

Illite

• Non-expanding• Moderate to low cation

exchange capacity• Fibrous or thin irregular

platelets• May migrate• May be susceptible to

damage on drying in cores

AluminaAlumina

SilicaSilicaKK

1010 ÅÅ

AFES Seminar

Smectite

• Expanding• High cation exchange

capacity• Honeycomb or cornflake

texture

• May swell and migrate

SilicaSilica

H2O, Na, Ca, Mg

AluminaAlumina

1010 -- 1717 ÅÅ

AFES Seminar

Illite-Smectite Mixed Layer

• Moderately high cationexchange capacity

• Platey or fibrous

• May swell and migrate

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Sample Cleaning

••Hot SoxhletHot Soxhlet

••Cool SoxhletCool Soxhlet

••Dean and StarkDean and Stark

•• ImmersionImmersion

••FlowFlow--throughthroughcleaningcleaning

Flow (cold) solvent

400 psi

FLOW-THROUGH

Condensed solvent (hot) liquid

SOXHLETSolventVapour

Methanol

Toluene

Toluene

Methanol

Methanol

AFES Seminar

Sample Drying

••Convection oven dryingConvection oven drying ~ 100C

••Humidity oven dryingHumidity oven drying 60C & 40% RH (or similar)

••Vacuum oven dryingVacuum oven drying ~ 60C

••Critical point drying using liquid COCritical point drying using liquid CO22

••Brine saturationBrine saturation

AFES Seminar

Porosity

AFES Seminar

Porosity

Porosity Precision ± 0.005 (or better)Grain Density Precision ± 0.01g.cm-3

•Vb, Bulk Volume•Vg, Grain Volume•Vp, Pore Volume, Porosity

Vb = Vg + Vp

= Vp/Vb

GD = Wt/Vg

VpVp

VgVg

Vb

AFES Seminar

Orthorhombic PackOne Grain Size

= 0.395Tetragonal-Sphenoidal Pack

One Grain Size

= 0.312

Rhombohedral PackOne Grain Size

= 0.26Cubic PackTwo Grain Sizes

= 0.25

Effect of Packing and Sorting

AFES Seminar

Porosity Definitions

Total Porosity, Neutron log

Total Porosity, Density log

Absolute or Total Porosity

Humidity-dried Core Porosity

Capillarywater

Quartz Claylayers

Smallpores Large pores Isolated

poresClay surfaces& interlayers

Vshale

Oven-dried Core PorosityMatrix

Hydrocarbonpore volume

Structuralwater

Hydration orclay-bound

water

Irreducible orimmobile water

**

**

(after(after EslingerEslinger && PevearPevear, 1988), 1988)

Relative volumes ofcapillary water and

hydrocarbons varieswith height above FWL

* if sample completely disaggregated

Volume dependent onQv of rock and

salinity of pore water

Neglible inmost rocks

AFES Seminar

Grain Volume Measurement

Boyle’s Law - Shared Volume

VrVr

He

Vc

Vg

PressureRegulator

valvevalve

ReferenceVolume

transducer

P1P2

SampleChamberSample

Chamber

P1Vr = P2 ( Vr + Vc - Vg )

g = Wd / Vg

AFES Seminar

Porosity - SUMMARY

• Variations exist for definition of effective porosity

• Logs and cores can almost always provide similar total porosity

• Porosity is

–Independent of grain size

–Dependent on sorting, packing, shape, cementation• Fracture porosity contributes little, generally

• Accurate methods available for determining Porosity

AFES Seminar

Permeability

AFES Seminar

Permeability

LAPK

Q.

..

Assumes:Assumes:••laminar flowlaminar flow••no reaction between fluid and rockno reaction between fluid and rock••one phase flowingone phase flowing••incompressible fluidincompressible fluid

AFES Seminar

Liquid vs. Gas Permeabilities

Liquid Gas

Finite velocity at wallVwall = 0

Vmax

AFES Seminar

Gas Slippage

Pressure Effect Conduit Size Effect Molecular Weight Effect

Lower pressure= greater slippage

Smaller conduit= greater slippage

Lower weight= greater slippage

AFES Seminar

Klinkenberg Plot

k

k

Air

CO2

1 / Pm

bHe . k

mPb

kk 1

Helium

0

AFES Seminar

Gas Permeability - Steady State

Hassler Cell

Gas permeability, 5% to 20%,dependent on permeability range

To Vacuum

Sleeve Pressure

Calibrated Orifice

P upstream P downstream

Core Plug

PressureRegulator

Kair =Permeability, millidarcies

Qa =Flow rate, cm3/sec, at Pa

=Viscosity of air, cpL = Length of sample, cmA = Cross sectional area of sample, cm2

P1 = Upstream pressure, atm

P2 = Downstream pressure, atm

Pa = Atmospheric pressure, atm

A)P-(PLQP2000

K 22

21

aaair

AFES Seminar

Gas Permeability - Unsteady StatePressure Transducer

Helium/Nitrogen Tank(manifold)

HydrostaticConfiningPressure

Carousel

AxialLoad

Core Samples

Computer

Gas escapesthrough core toatmosphere

Open valve forpressure drawdown

P1

P2

t1 t210

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50

Time, seconds

Pre

ssu

re,p

sig

21 PPP

Instantaneous Flow ratedetermined from slope at P

P1

P2

t1 t210

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50

Time, seconds

Pre

ssu

re,p

sig

21 PPP 21 PPP

Instantaneous Flow ratedetermined from slope at P

CMS-300

AFES Seminar

Forchheimer's Equation

2

kdLdP

dLdP

0

Inertial

Viscous

0

Acceleration in pore throatAcceleration in pore throat

Deceleration in pore bodyDeceleration in pore body

kdL

dP

AFES Seminar

Overburden Porosity & Permeability

1.0

0.8

0.6

0.4

0.2

2000 4000Sleeve Pressure (psi)

Fra

ctio

nof

base

poro

sity

Porosity

Well cemented Friable Unconsolidated

1.0

0.8

0.6

0.4

0.2

2000 4000400Sleeve Pressure (psi)

Fra

ctio

nof

base

perm

eabi

lity Permeability

AFES Seminar

Permeability vs. Porosity

1

10

100

1000

0 5 10 15 20 25 30 35

Porosity, %

Per

mea

bilit

y,m

d

Fine GrainedFriable Sand

ChalkyLimestone

IntercrystallineLimestone andDolomite

Well CementedSand

Sucrosic Dolomite

Reef Limestone

Oolitic Limestone

AFES Seminar

Core Analysis Objectives

•Reservoir QualityPore geometry, mineralogy, cements, clays, depositional environments

•Petrophysical PropertiesPorosity, permeability, effects of stress, effective porosity

•Water SaturationElectrical properties, capillary pressure, Dean Stark if OBM

•Saturation ChangeRelative permeability, gas or water injection, recoverable hydrocarbon

•Rock MechanicsCompressibility, sanding, fracture design, stimulation

CUT CORE!

AFES Seminar

CORE LABORATORIES (U.K.) LIMITED