Data acquisition and Log Evaluation in a High-Density Cesium Formate Fluid

KvB production wells
Data acquisition and log evaluation in
a high density Cesium formate fluid
Part 2 ofPart 2 of SPE/IADC 105733SPE/IADC 105733
Erik S. Pedersen, Statoil ASA

2
Log evaluation in high density Cs formate mud
• Outline
– Properties of formate mud in a logging/formation evaluation perspective
– Challenges wrt. to log evaluation when drilling wells using low particle Cs
formate mud.
– Examples of typical LWD and wire-line log responses
– Improve the understanding of the Cs logging environment
– Understanding the density tool
– Present a novel solution on how to correct the density log
– How calculate the invaded zone saturation (Sxo) and
the formations density-porosity (PhiD)
– Summary/Conclusions
SPE/IADC 105733SPE/IADC 105733

3
The Kvitebjørn Field
• Kvitebjørn is a HPHT
gas/condensate field in block
34/11, located in the South-
Eastern part of the Tampen Spur
area in the North Sea.
• Water depth: 190 m
• Reservoir: Brent Group
• Reservoir thickness: 160-190 m
• The reservoir depth: 4100 mTVD
• Reservoir temperature: 150-155°C
• Reservoir pressure: 770 bar
• Gas: 2-3% CO2 ,<10 ppm H2S.

4
Physical and nuclear properties of high
density formate brines
Saturated RhoFL Veloc. Res. Pe HI Sigma RhoE
Formate brines:_ [g/ccm] [m/s] [ohmm] [barns/e] [-] [c.u.] [g/ccm]
NaCOOH brine 1.351 1880 0.104 0.5 0.82 21.1 -
KCOOH brine 1.59 1960 0.087 3.6 0.51 29.5 -
CsCOOH brine 2.34 1550 0.070 259 0.50 201.5 2.15
KvB Cs/K brine 2.03 - 0.062 163 0.62 122.0 1.95
(27% KCOOH brine & 73% CsCOOH brine + 40 kg CaC/m3 and polymers, @ 25 degC).
KvB @150 degC 1.96 - 0.014 157 0.60 118.0 1.89
__________________________________________________________________
Formate brines are high density particle free mud systems i.e.
the density of the invading mud filtrate is ~identical to the density of the mud it self.

5
The engagement in understanding logging tool
responses in this ‘new’ logging environment
•Halliburton and Saudi Aramco performed laboratory measurements
and numerical modeling on low-density sodium/potassium formate
fluids (2005).
•Baker Atlas and BP carried out a similar work on medium-density
cesium/potassium formate brines (2002).
•Schlumberger and Statoil conducted an extensive calibration study on
high-density cesium/potassium formate brines (2004).
•The focus of the published works have been on laboratory
measurements, borehole effect, and the influence of formate fluids on
the response of the electrical wire-line tools.

6
Challenges with high density formate muds
• Like water-based mud filtrate; will invade water-wet permeable intervals
• High concentration of ions causes abnormal conductivity behaviour
• Large density contrast between invading fluid and reservoir fluid
(For the Kvitebjørn field; 1.96 g/cc versus 0.38 g/cc.)
• Low electron density of Cesium
• Cesium high photoelectric cross section will cause an elevated density response
• Potassium content about 30% higher than in ordinary KCl mud
• Both Cesium and Potassium have low Hydrogen Index
• Cs high capture cross section (sigma) will reduce neutron response
• Invasion profile varies with time
• The logging tools transformation of the electron density to apparent density are
designed for water and oil.

7
How do we “transform” these challenging log
responses to useful and quantitative logs ?

8
How do we “transform” these challenging log
responses to useful and quantitative logs ?

9
Solutions to the challenges
•Consider invasion of filtrate as a benefit – not as a problem.
•Utilize the unique nuclear properties of Cesium.
•Dealing with invasion in general requires close attention to the mud
filtrate properties and the logging environment:
– The elemental compositions of the mud
– Resistivity and density characteristics of the mud
as function of temperature and dissolution
– Good knowledge of the applied logging tools
– Awareness of “time lapse” effect on the log responses

10
What makes formate fluids different from other
drilling fluids with respect to log responses ?
• 1. Filtrate invasion effects
Any formate filtrate invasion in
water wetting sand and gas filled
reservoirs will create an invaded
zone containing a fluid that is up to
twice as dense as the native
reservoir water.
The calculation of the average fluid-
density in the invaded zone is very
sensitive to the calculation of the
filtrate saturation Sxo
Red; drill data, Black; ream data

11
• 2. Effect of gravity segregation of
filtrate; “Time Lapse”
The high density contrast between the
filtrate and the fluids present in the
formation results in gravity segregation
taking place.
The combined effect of seepage loss
and gravity segregation are controlled
by many factors; mud design/seal
horizontal permeability vs. vertical
permeability, capillary conditions,
porosity, overbalance, depletion, time
after drilling, etc.
Red; drill data, Black; wire line data

12
• 3. Effect of conductivity
The total amount of ions in
formate are very high.
At high formate concentrations
the resistivity of the fluid
actually increases with
increasing fraction of formate.
However, at high temperatures
the resistivity of the filtrate can
be treated as a constant value
over a wide range of
concentrations.
Synthetic formation water blended with
1.96 sg. Csk mud filtrate (RO1469)
Resistivity at different temperatures
0.000
0.010
0.020
0.030
0.040
0.050
0.060
0.070
0.080
0.090
0.100
0.110
0.120
0 10 20 30 40 50 60 70 80 90 100
Volum% CsK filtrate
Resisitivity(Ohm*m)
25 °C
50 °C
75 °C
100 °C
125 °C
150 °C

13
• 3. Effect of conductivity cont.
In the range of 30-80% vol%
formate, often the mixtures of
formate and formation water
results in resistivity values
lower than the two original
fluids.
Resistivity of KvB MDT water samples compared to
Arp's applied on synthtic formation water
and wellsite mudfiltrate sample
0.000
0.010
0.020
0.030
0.040
0.050
0.060
0.070
0.080
0.090
0.100
0 25 50 75 100 125 150 175
Temperature [°C]
Resistivity[Ohmm]
MPSR929 ~22 vol% CsK
Valemon formation water
Wellsite Rmf by Arp's
MPSR786 ~59 vol% CsK
100% CsK mud filtrate

14
• 4. Unusual nuclear properties
The presence of “heavy” elements as Cs (also Ba and partly K) changes
several nuclear properties of the drilling mud dramatically. Especially the
photoelectric cross-section, the electron density, the thermal neutron cross-
section and the hydrogen index.
1220.621631.9532.032.03 s.g. Cs/K formate
2020.502592.152.342.34 s.g CsCOOH
1480.551991.9822.092.09 s.g. Cs/K formate
-0.791201.5101.501.50 s.g. Cs/K formate
210.781351.641.74Fresh water barite mud
1270.891.301.171.18NaCl saturated water
Σ
c.u.
HIPe
b/e
ρe
g/cc
ρbulk
g/cc
Fluid
The photoelectric
cross-section of mud-
filtrate from NaCl
WBM or high s.g.
Barite OBW/WBM are
typically 1-2 b/e,
while Cs formate
filtrate has values of
100-200 b/e.

15
• 4. Unusual nuclear properties cont.
Also the nuclear properties of the formate muds differ significantly from the
nuclear properties of the different common lithologies.
The photoelectric cross-
section of typical
lithologies are 2-5 b/e.,
while Cs formate filtrate
has values of 100-200
b/e.
Also the electron density
of Cs
differs significantly from
the physical density.
1.9531632.032.03 s.g Cs/K formate
2.653.422.65Shale
2.412.702.39Shaly sandstone
2.331.752.31Clean Sandstone
0.9480.1190.85Oil
1.1850.8071.09Salt water
RhoE
[g/cc]
Pe
[barns/e]
RhoB
[g/cc]
« Lithology »

16
Understanding the density log
The various density logs actually
measure the electron density, RhoE,
of the medium by measuring the
gamma spectrum in the areas where
the compton scattering dominates.
With increasing density the gamma
ray intensity will be reduced in the
entire spectrum.
True bulk density, RHOB, is given
by:
RhoB = RhoE*A/(2*Z)
Where Z is the proton (electron)
number, and A is the atomic weight.
For most atoms relevant to logging;
A=2*Z
thus: RhoB = RhoE

17
Understanding the density log cont.
• For heavy elements the assumption
N=Z no longer yields. Due to
coulomb forces, heavy nucleus need
an increasing number of neutrons to
be stable.
• This causes the measured “electron
density” to under-estimate the
density of the element by approx.
20%.
• However, the high number of
electrons in heavy atoms increases
the number of absorbable photon
energies exponentially:
Pe=(Z/10)3.6
A=55+77=132
while
A=2*Z=2*55=110

18
Understanding the density log cont.
– Extreme density contrasts of the fluids; gas vs. formate filtrate
– The presence of Cs do totally dominate any pef response
– Several nuclear effects affecting each other:
Compton scattering, photoelectric effect, large nucleus effect
– The transformation from electron density to apparent bulk density
is designed for water and oil cases; RhoB=1.074*RhoE-0.1883
– Rib & spine corrections being applied to the apparent bulk density
Confused ?
A need for a novel method based on the logging tools
“answer-products”: ROBB and PEB from Schlumberger ADN6 tool.

19
Correcting the density log
• Several numerical calculations and
experiments have verified a volume-
linear response from 0-70 b/e for the
applied LWD density tool.
Thus (equ.1):
PhiT =porosity of the porous media
Sxo = saturation of the invading filtrate
C = Concentration parameter for Cs
Pe_Lith=The combined Pe effect from
matrix, formation fluids and standoff.
LithPeCSxoPhiTPe _+⋅⋅=
Logged PEB/PEFvs. calculated photoelectric
cross section index
0
10
20
30
40
50
60
70
80
0 10 20 30 40 50 60 70 80
Calculated photoelectric factor
PEB/PEF
Tool X
ADN calc
ADN snupar

20
Correcting the density log cont.
• Extremely good linearity observed
between the required correction of
the density (ROBB) and the logged
PEB.
Thus (equ.2):
ROBB=Density from the ADN tool
PEB=Photoelectric factor from the
ADN tool.
Pe_Lith=Photoelectric “base line”
ADN6 ROBB vs. PEB responce in 8" bore hole
y = 0.1714x + 1.0578
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
0 10 20 30 40 50 60 70 80
ADN measured PEB responce
Necessaryreductioninmeasuredbulk
density
RHOB Expt 4 inch invasion
Linear (RHOB Expt 4 inch
invasion)





 −⋅
−⋅=
100
)_(1714.0
1_
lithPePEB
ROBBcorrRhoB

21
Correcting the density log cont.
Substituting the standard density
porosity equation (equ. 3):
into equ.1:
and solving for Sxo, results in
(equ.4):
ADN6 RHOB corrected by PEF
2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8
Theoretical physical bulk density
MeasuredbulkdensityRHOB
PEF-correctedRHOB Measured RHOB
PEF corrected RHOB
Cs 1.50 33 p.u.
Cs 1.50 17 p.u.
Cs 2.09 33 p.u.
Cs 2.09 17 p.u.
( )[ ]RhoGgpSxoRhoMFSxoRhoMA
RhoBRhoMA
PhiT
⋅−+⋅−
−
=
1
LithPeCSxoPhiTPe _+⋅⋅=
)_(
)_(
LithPePEB
corrRhoBRhoMA
CRhoGASgpRhoMF
RhoGASgpRhoMA
Sxo
−
−
⋅+−
−
=

22
Estimating density porosity
Finally, applying the expression for
Sxo with the corrected density log
and solving for porosity gives the
final density porosity (equ.5):
(equ. 2):





 −⋅
−⋅=
100
)_(1714.0
1_
lithPePEB
ROBBcorrRhoB
[ ]RhoGASSxoRhoMFSxoRhoMA
corrRhoBRhoMA
CsPhiD
⋅−+⋅−
−
=
)1(
_
_

23
Estimating porosity cont.
• This novel method do produce a
final bulk formation density and a
log derived density-porosity which
matches the core porosity in
different formation in three different
wells.

24
Net reservoir definition
• Combining the drilled resistivity
with the reamed resistivity and
reamed photoelectric factor results
in a robust and consistent Net
reservoir definition.
• High resolution image logs reveals
sedimentary features on cm scale.
high quality image logs provides the
geo-modelers with detailed
information regarding structural dip,
sedimentary features for
depositional environment
interpretations and orientation of
sand-bodies.

25
Dip and depositional interpretation
Bioturbated mudstoneLaminated mudstone with
drill induced fractures

26
Conclusions
•Full open-hole formation evaluation of the Kvitebjørn reservoir has
been carried out with LWD tools.
•The evaluation has been aided by the development of a novel logging
interpretation solution for a LWD density tool, which makes unique use
of the extremely high photoelectric effect of cesium-rich filtrate.
•Using PEB and ROBB data, combined with resistivity measurements
from both the LWD drill pass and the ream pass, produces a very
reliable and consistent net reservoir definition.
•The final interpretation results matches the core porosity from different
lithologies in 3 different wells.

Data acquisition and Log Evaluation in a High-Density Cesium Formate Fluid

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

Similaire à Data acquisition and Log Evaluation in a High-Density Cesium Formate Fluid

Similaire à Data acquisition and Log Evaluation in a High-Density Cesium Formate Fluid (20)

Plus de John Downs

Plus de John Downs (20)

Dernier

Dernier (20)

Data acquisition and Log Evaluation in a High-Density Cesium Formate Fluid