An excursion through water saturation methods from cased ... · An excursion through water saturation methods from cased hole logging Chiara Cavalleri Principal Petrophysicist, Schlumberger

Schlumberger-Private

An excursion through water saturation methods from

cased hole logging

Chiara Cavalleri

Principal Petrophysicist, Schlumberger

London, 13-Dec-2018

Schlumberger-Private2

▪ Introduction

▪ Formation evaluation behind casing

▪ Saturation methods and examples

▪ An integrated approach

▪ Summary

Outline


▪ Cased-hole formation evaluation has a primary role for the proper description of the existingreservoir systems; but also new players in particular conditions.

▪ Help finding that additional drop of oil

▪ Assisting completion design or intervention programs

▪ Characterization of new reserves managing costs and operational risks.

▪ Alternative saturation methods are available behind casing; with or without open hole logs

▪ Current technology is the enabler, even in tough logging conditions.

Introduction


▪ Logging behind casing…mostly with open hole logs….with its own value and limitations.

Petrophysics Logging Behind Casing

Sigma and Full Spectroscopy Large

Pulse neutron and Spectroscopy Slim

Pulse neutron, Inelastic GR, Full Spectroscopy Slim

0 5 10 15 20

CH res. slim

CH resistivity large

CH Density

Acoustic Wide Band Frequency

Acoustic Slim

Neutron Poro Thermal

Neutron Porosity Epithermal

Spectral Gamma Ray

Gamma Ray

Casing or hole size rangeCasing / Completions

Single Multiple

×× ×× ×××× ×× ××××× ×× ×


Needs to consider many diverse conditions

▪ Open hole log availability: yes/no

▪ Formation water salinity: fresh/saline, known/unknown

▪ Lithology: known/unknown, simple/complex

▪ Hydrocarbon type: oil, gas, mixed, kerogen?, bitumen?

▪ Other: CO2; dynamic conditions,…

Saturation

1. Sigma

2. Sigma + Resistivity

3. Carbon/Oxygen

4. TOC

5. FNXS

Petrophysics Logging Behind Casing


▪ Water saturation when formation water salinity has sufficient contrast with hydrocarbon and rock

▪ Lithology and porosity effects

Water Saturation from Sigma Log

Slog = Vmatrix * Smatrix + Vclay* Sclay + fSw Sw + f(1-Sw) Sh

MaterialSigma (c.u.)

TPHI

Quartz 4.55 –0.03

Calcite 7.08 0.00

Dolomite 4.70 0.03

Wet Illite 21.00 0.34

Kerogen (CH 1.3g/cm3) 20.18 0.98

Water 22.20 1.00

200ppk NaCl water 99.9 0.93

Diesel (CH1.8 0.89 g/cm3) 23.30 1.08

CH4 (0.15 g/cm3) 7.50 0.21

CO2 (0.6 g/cm3) 0.03 –0.12


Saturation from Sigma in Depleted Reservoirs; Complex Wellbore configuration

Raw Measurement Interpretation Saturations

Depleted zone

Saturation at original condition

Tubing, Casing (in) Borehole (in)

7 (casing) + 9-7/8 (Casing) 12.25

• Formation type: Clastic, 20% porosity; 50ppk salinity (found

to be variable)

• Borehole fluid CaBr2 and formation oil; chrome tubing

Formation salinity change; fresher

Tubing, Casing (in) Borehole (in)

4.5 (Tubing),

7 (casing) + 9-7/8 (Casing)

12.25


▪ Classical measurement for cased hole reservoir monitoring of oil content and fresh water conditions

▪ Rw independent

Dynamic range

function of porosity

and oil carbon density

Oil Saturation from Carbon/Oxygen Logging

FCOR vs NCOR

(Yields)

Carbon/Oxygen


Oil Saturation from Cased Hole Carbon/Oxygen Spectral Analysis

▪ Shaly sand formation; low unknown salinity

▪ Bypasses oil from Carbon/Oxygen logging in absence of complete open hole logs – standalone cased hole evaluation

Cased

hole FE

Far and Near C/O

Yields Ratio

Oil Volume and

Saturation from C/O


▪ Total Carbon (TC) is measured;

▪ Minerals are computed

▪ Inorganic carbon is calculated from mineralsTIC = 0.120*Calcite + 0.130*Dolomite + 0.104*Siderite + 0.116*Ankerite

Inorganic Carbon from Minerals

TOC

MineralsCarbon

TC TIC- = S(oil)

Shc =TOC · rma · (1-fT)

rhc · Xhc · fT

Oil Saturation from Spectroscopy (TOC)

▪ Organic Carbon (TOC) = TC - TIC

▪ S(oil) is computed from TOC and Porosity

Elements,

Matrix,

Minerology,

Full Closure Spectroscopy

SPE # 166297, 2013


Oil Saturation from Cased Hole In-Situ Total Organic Carbon Measurement

▪ Shaly sand formation; low unknown salinity

▪ Bypasses oil from Carbon/Oxygen logging in absence of complete open hole logs – standalone cased hole evaluation

Cased

hole FE

Far and Near C/O

Yields Ratio

Oil Volume and

Saturation from C/O

Shc =TOC · rma · (1-fT)

rhc · Xhc · fT

SPE # 186957-MS 2017


TOC Independent Oil Volume in variable Salinity and Porosity

8.75” BS; 7” Casing; 50 ft/hr

Neutron

Density

Spectroscopy,

C/O

CH Shc

0 1

Cased Hole

Open Hole

Volumetric

interpretation

N-D

Porosity

50 p.u. 0

Porosity

50 p.u. 0

Spectroscopy

Oil wt%

0 wt% 18

Spectroscopy

Dielectric

OH Shc

0 1

100 ft

• Heavy oil under steam-injection (EOR)

• N-D crossover

• Resistivity fails

• Oil Saturation from TOC in good

agreement with C/O analysis

• Solving for complex mineralogy


▪ Critical present day oil saturation from TOC

▪ FSAL estimate from Sigma, also shedding light on the complex reservoir environment

Petrophysics and well integrity logging behind 11.875in casing; in front of 14.5in bit size

High Def spectrosco

py

Well integrity

Formation testing

Cased Hole Spectroscopy in large hole – 9 Years After Drilling

XX600

XX500

XX400

XX300

XX200

XX100

XX000

XX700


▪ Probability of fast neutrons to interact with atoms; directly sensitive to gas filled porosity

▪ Quantify gas volume in low porosity rock together with Sigma and neutron porosity logs.

Gas Saturation from Fast Neutron Cross-section New Measurement

Detected

inelastic GR

0 0.2 0.4 0.6 0.8 15

5.5

6

6.5

7

7.5

8

8.5

HI

FN

XS

(1

/m)

fresh water

CH4 (0.1g/cc)

Sg 0%

Sg 100%


Saturation from Gas (FNXS) Inelastic hydrogen in Tight Gas Sand

Producing oil and gas field; shaly sand formation with low porosity gas-filled and very low porosity alternating.

8.75-in bit size, 4.5 in casing; 11.6 lbm/ft casing weight with cement thickness more than 2 in.

Mineral Solver

FNXS

TPHISIGM

claygaswaterquartz

clayclaygasgaswaterwaterquartzquartz



VVVV

FNXSVFNXSVFNXSVFNXSVFNXS

TPHIVTPHIVTPHIVTPHIVTPHI

SIGMAVSIGMAVSIGMAVSIGMAVSIGMA

+++=

+++=

+++=

+++=

1


o Shaly sand, variable rock quality;

o Casing and tubing, open perforations; crossflow conditions

o FNXS Fast Neutron Cross Section; environmental corrections applied to

account for different conditions than EECF.FNXS vs TPHI analysis value

Sg

0%

Sg 100%

Fast Neutron Cross Section Measurement Applied to Petrophysics


Three Phase Saturations Computation in Carbonate

Differentiate Gas Filled Porosity from oil filled rock; variable porosity

Mineral Solver

FNXS

TPHI

Elements Dry

Weights

SIGM

Standalone cased hole evaluation

calcitegaswaterquartz

quartzquartz

calcitecalcite

calcitecalcitegasgaswaterwaterquartzquartz



VVVV

DWSIVDWSI

DWCAVDWCA

FNXSVFNXSVFNXSVFNXSVFNXS

TPHIVTPHIVTPHIVTPHIVTPHI

SIGMAVSIGMAVSIGMAVSIGMAVSIGMA

+++=

=

=

+++=

+++=

+++=

1


ELAN Multi-mineral analysis integrating

Pulsar measurements

• Standalone evaluation of rock and fluids, through quantitative use of FNXS with Sigma, TOC, and full spectroscopy recorded behind

casing

• Multi-mineral solver plot with reconstructed curves and computed rock and fluid volumes:

Mineral Solver

FNXS

TPHI

Elements Dry

Weights

SIGM

Three Phase Saturations behind Casing and Another Complex scenario

SPWLA 58th, 2017 – Solving for reservoir saturations using multiple formation property measurements from a single PNL tool


Saturation Calculation and Monitoring Behind Casing - Summary

Condition SIGM RT C/O TOC FNXS Remarks

f<15% (low f) Limit on RT,max

15%<f, Csalt<20 ppk (fresh) Limit on RT,max

15%>f, Csalt>20 ppk (saline) Favorable contrast conditions

Mixed salinity Need Csalt profile

Flowing well Need Yo measurement

Fluid contact in hole Inaccurate near contact

Washed-out holes Shallow DOI on C/O

Near wellbore effect Shallow DOI on C/O

Acid effect Effect of high S acid element

Run in small tubing Slim measurement available

Multiple casing/tubing string with good calibration

Deviated/HZ well Conveyance dependent

Lithology Need matrix data

Ref.: after Aulia et al., 2001 (Schlumberger) - extended

State of art technology and Integrated approach help reducing Sw uncertainty in complex setting


• Alternative methods for saturation measurement from logs behind casing and within completion exist.

• The results can be obtained as a standalone measurement approach or data integration to open hole.

• The choice of the logging program and computational workflow depends on the logging environment and its complexity; and the particular evaluation objective.

Conclusions


Paper # • Paper Title • Presenter Name

Slide 26

An excursion through water saturation methods from cased ... · An excursion through water saturation methods from cased hole logging Chiara Cavalleri Principal Petrophysicist, Schlumberger

Documents