Super ComboThe previous generation

CNT, LDT, NGT

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– The primary purpose of running basic open hole logs is to provide petrophysical evaluation of subsurface formations.

– Our clients want to know how much oil and/or gas is down hole. We cannot do this directly BUT provide the

information necessary to determine the volume of water downhole, from which the volume of hydrocarbons can be inferred.

Sw + Shc = 1

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SR

Rww

t

22

SaR

Rwn w

mt

Simplified to :

Archie’s equation :

So what do we have :CNL/LDL give us porosity & density of formationMSFL/ Laterlog + Induction tools give us resistivityBV Sww

BVhc Shc

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Intro

LDT CNT NGT

Am I going back in time ????Why would I want to discuss these tools????

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A slide we often see in PEX presentations

Compares the length of the HILT with

The old super combo.

But true to SLB ways never put down the

Old for the new.

A slide you will see less often

Supercombo PEX

90 ft

38 ft

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The Ratings for the Super combo (as well as the cheaper pricing) has kept it in the market.

TEMP. PRESS.

DESCRIPTION TOOL (F) (kpsi)

Micro Spherically Focussed SRT - C 350 20 Litho Density Tool LDT - D 350 20 Compensated Neutron Tool CNT - G 400 20 Compensated Neutron Tool CNT - H 400 20 Spectroscopy Tool NGT - D 300 20 Platform Express PEX* 250 10 (* not including resistivity sensors)

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Let’s start with the LDT…

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Principal Applications

• Determining the formation density

• Determining the formation lithology

• Determining the formation porosity.

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Gamma Ray Interactions - Review• High Energy GR emitted from chemical source• Reacts with matter in formation• Type of interaction dependent on GR energy level• Source used is Cesium-137, 662 Kev• Hence Compton Scattering and P.E. Absorption occur

Photoelectric Absorption

Compton Scattering

Pair Production

GR < 100 Kev GR > 100 Kev

GR > 1.02 Mev

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Density Physics - Compton Scattering

Ne = Rhob * Z * Na / A

Rhoe = Rhob * ( 2 Z / A)

## ( 2 Z / A) ~ 1

Rhoe Rhob

Electron density index and Bulk Density

(Ne) Number of electrons in one gram-atom(A) Atomic weight - the mass of an atom (grams/gram-atom).(Z) Atomic number (Z) - the number of electrons in a neutral atom (electrons/atom).(Na) Avogadro's number (Na ) - the number of atoms in a gram-atom

(6.02 x 1023 ).(Rhob) Bulk density(Rhoe) Electron density index

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Density Physics - Photoelectric Absorption

• Reaction occurs at Low Energy GR < 100 Kev

• GR interacts with shell electrons Absorption

• Shell electrons related to Z Atomic number

• Higher Z means higher PE absorption

• Count the GR reaching tool after the interactions

measure PEF (PEF = (z/10)3.6

)Knowing ... PEF (Z) LITHOLOGY

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Density and PEF - common minerals

and liquids

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So what’s the difference …

2 detectors…

Spine and Ribs…

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Increasing hmc

@ hmc=infinityTool reads mud density

Actual Formationdensity

nls

nss

When Ln (nLs), Ln (nss) is plotted we obtain the straight

line called the Spine.

In the logging environment the points do not fall on the Spine

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Enough Density!!!

CNL….

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Principal Applications

Porosity Analysis Lithology Identification Clay Analysis Gas detection

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Formation Interaction

NeutronSource

Short SpacedDetector

Long SpacedDetector

BoreholeFormation

ThermalPhase

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Neutrons

• Fast Neutrons with energy in excess of 0.1 MeV.

• Epithermal Neutrons with energy between 10 eV and 0.4 eV.

• Thermal Neutrons in thermal equilibrium with their surroundings with an average kinetic energy of 0.025 eV .

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Life cycle of a Neutron….NEUTRONSOURCE

TIME ( µ s)

CAPTUREAVERAGETHERMALENERGY.

025 EV

.4 eV

10 eV

100

ENERGY LEAVING SOURCE

1 10

01

1

102

104

106

APPROX. EPITHERMAL

ENERGY REGION

NE

UT

RO

N E

NE

RG

Y (

e V

)

Diffusion & Capture

Slowing down

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Element Atomic No.

Element Symbol

Capture Cross Section

(Barns)

Scattering Cross Section

(Barns)

Average No. of Collisions to reduce Neutron energy from

2MeV to 0.025eV

1 H 0.3 20 186 C 0.0032 4.8 1158 O 0.0002 4.1 150

14 Si 0.13 1.7 26117 Cl 31.6 10 32948 Cd 2500 5.3 1028

3 significant elements …

HYDROGEN very effective in slowing down Neutrons

CHLORINE is a good absorber (Capture)CADMIUM - excellent as a shield

Hydrogen Index = grams of H/cc in the formation

grams of H/cc in H20 at 75C

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but….

GAS EFFECT : In gas-filled pore space, the hydrogen density is much less than if the same pore-space is liquid-filled. CNT reads much less than if the same pore space is liquid-filled.  

SHALE EFFECT :Shales contain a high concentration of hydrogen in the form of hydroxils associated with the shale matrix. CNT will read a high apparent porosity in shale.

EFFECT OF NEUTRON ABSORBERS :If the formation contains neutron absorbers like Chlorine or Gadolinium, then the number of thermal neutrons reaching the detectors shall be reduced. C NT will read less porosity

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CNT LQC…

SST 0 -20 p.u. +/ - 1p.u. TALP < 1 +/ - 0.2

LST 30 p.u. +/ - 2p.u.

DST >45 p.u. +/ - 6p.u.

AHY

SALT

COAL

SHALE

CNL

n poor in high porosity b/ c low count rates

high HI = low count rate = high stat fl ucuations

-0.2 p.u.

-0 p.u.

38-70 p.u.

30-60 p.u.

NPHI

-1.7 p.u.

0 p.u.

2.4 p.u.

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NGT – Natural GR Spectrometry

Uses of GR:

• -  Definition of shale beds

• -  Indicator of shale content

• - Detection of radioactive and non-RA

minerals

• -Identification of formation tops

NGS Applications

• -Identification of radioactive sands

that may be misinterpreted as shales

• - Identification of different types of

shales/clays

• - Complex lithology analysis.

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Measures :

# gamma rays

the energy level of each (i.e. Spectrum)

=> permits the determination of the concentrations of

RA K, Th & U

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The tool it self

• Cartridge below the sonde.• 12” long, 1 ¾” diameter NaI optically

couple with a photomultiplier.• Uses ref GR source Am 241 – for

continuous energy  calibration of the tool behavior of the detector vs temp is

unpredictable so stabilization is essential.

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NGT LQC…

SST APLW 900 - 1100 cps

LST APUW 900 - 1100 cps

DST DHVF +/ - 5 V around the mean

AHY LQCL +/ - 1

SALT LQCU +/ - 1

COAL CHI < 6

SHALE

VBAR = 1 in heavy muds value will

decrease. Change CBAR value to the

correct reading.

detection of tool response

f rom theorectical value

Repeatabilty depends on a # of

variables:

logging speed

conc. WRT each otherNGS

10 to 20

8 to 15

8 to 15

< 30

> 75

15 to 30

8 to 15

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Carbonate Reservoirs

• Thorium and Potassium shale or marls• Uranium organic material (bituminous rock,

source rocks), stylolites, ( with insolubles) or phosphates.

=> Here the thorium, potassium and CGR curve is a more accurate indication of shaliness

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Sandstones• Thorium clay content • Potassium Mica, Potassium Feldspars, Ilite

Uranium organic matter

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So why the Super Combo …. • PRICE:

The super combo is at least 30% cheaper than the PEX.

Cheap Rig time – big buyers• HI-temp deep wells – over PEX ratings

– Super combo usually the best alternative

• Winner of market share where client is resistant to change