B - Search and Discovery

New NMR-Based Methodology for Inferring the Presence of Movable Heavy Oil in Reservoir Layers*
Pedro A. Romero1, Nestor Acosta2, and Hiran Serrano3
Search and Discovery Article #40519 (2010)
Posted March 18, 2010
*Adapted from expanded abstract and slides prepared for oral presentation at AAPG International Conference and Exhibition, Rio de Janeiro, Brazil, November
15-18, 2009
1
Baker Hughes Inc., Rio de Janeiro, Brazil ([email protected])
Baker Hughes Inc., Comodoro Rivadavia, Argentina
3
YPF S.A., Comodoro Rivadavia, Argentina
2
Abstract
The present contribution is the result of the authors’ several experiences in the NMR analysis of sandstone reservoirs with
argillaceous-tuffaceous matrix belonging to geological formations of Cretaceous age. It is intended to highlight the advantages and
synthetically show the main aspects of the use of NMR tools for characterization of movable heavy oil in continental clastic reservoirs
of the Gulf of San Jorge Basin in Argentina. The methodology presented is for inferring the presence of movable heavy oil in reservoir
layers of a fluvial environment. It is based on six main principal indicators:
 reservoir pressure
 development of spontaneous potential
 increase of the resistivity response of the layer
 the slope of the T2 log mean of the furthest right hand side lobe of the T2 distribution when plotted in depth
 the presence of water-based mud filtrate in the DT2 maps
 the NMR permeability
When these indicators are considered, the prediction of the layer can be forecast with high probability. This work specially describes
how NMR derived properties improve the fluid typing in these reservoirs. The present approach has been validated with measured
data from production tests.
Copyright © AAPG. Serial rights given by author. For all other rights contact author directly.
References
Acosta, N., 2008, Analysis of Nuclear Magnetic Resonance for characterization of continental clastic reservoirs, San Jorge Basin,
Argentina: Naturalia Patagonic Science Magazine.
Acosta, N., P. Romero, G. Magenta, G. Potas, C. Cabrera, C. Coccia, L. Di Benedetto, and L. Ferreira, 2007, Methodology for
characterization of a clastic reservoir based on correlations between electrofacies, NMR and image logs, A case study from San Jorge
Basin: 10th. International Congress of the Brazilian Geophysical Society and EXPOGEF, Rio de Janeiro, Brazil,
Acosta, N., E. Estrada, and B. Saavedra, 2007, Porosity variations by diagenesis in reservoirs of the Bajo Barreal Formation, San
Jorge Basin: Methodology of evaluation with logs: X Latin American and Caribbean Petroleum Engineering Conference, SPE #
108065, Buenos Aires, Argentina.
Breda, E., and M. Lucero (Repsol-YPF), 2005, Caracterización de los reservorios de la Formación Bajo Barreal Inferior Arenas y
Tobas (Sección Tobácea), VI Congreso de Exploración y Desarrollo de Hidrocarburos, 1, p. 197-214. Mar del Plata, Argentina.
Chen, S., G. Hursan, D. Beard, and D. Georgi, SPE 84481: G.TE Correction for Processing Multigradient, Multiple –TE NMR Log
Data. SPE, Texas, USA.
Domínguez, H., B. Saavedra, A. Corbelleri, and L. Sliwinsky, 2005, Uso de resonancia magnética nuclear para la caracterización de
reservorios y fluidos en yacimientos de la Cuenca del Golfo San Jorge, Patagonia, Argentina: VI Congreso de Exploración y
Desarrollo de Hidrocarburos, Mar del Plata, 1, p. 59-71.
Pedro A. Romero
Nestor Acosta
Hiran Serrano

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NMR Petrophysics
NMR Behavior Of Heavy Oil
Detection Of Heavy Oil – Field Example
Summary

NMR porosity measurement
◦ Calibrated to 100% water tank
◦ Amplitude of measured signal as % of calibrated signal
is NMR total porosity
100 pu ↔ Mcal
M log
Calibration
Tank
M cal

Mlog
NMR
Time

100
Echo Train
Amplitude
Amplitude
RF Pulses
90°x
180°y
180°y
Echo Signals
180°y
180°y
180°y
TE
Time
Echo Train
TW
Time
TE : inter-echo spacing time
TW : wait time ( ≥ 3 x T1 for full recovery)
NMR logging measures:
Amount of Magnetization of 1H present in the
rock sample independently of the lithology
Slow relaxation times
in large pores
Fast relaxation times
in small pores
Pore Geometry: Surface, Volume
1 / T2s = * S / V
Fluid typing: Viscosity
1 / T2b =  1200
Field Gradient: Diffusion
1 / T2d = [(* G * TE)2 ]*D / 12

NMR Porosity is defined by the equation
A = HI * T * (1 - e - TW / T1)
◦ HI - Hydrogen Index of fluid filling the pore space
Low hydrogen index of gas and light oil results in porosity
undercall
◦ T1 - Longitudinal relaxation time
◦ TW - Time between measurements at the same
frequency – TW ≥ 3*T1 for full recovery
MR Depth of Investigation
∆B0,A
∆ℓA
∆B0,A
= GA (Gauss/cm)
4
3
2
∆ℓA
f  B0
Depth of Investigation (inches)
5
1
0
1000
∆B0,B
fA, B0,A
∆ℓB
∆B0,B
fB, B0,B
900
800
700
600
Frequency (kHz)
= GB (Gauss/cm)
∆ℓB
fC, B0,C
∆B0,C
∆B0,C
∆ℓC
∆ℓC
ℓA ℓB ℓC
Efficiency….Data
accuracy….People-oriented
service
D.O.I.
= GC (Gauss/cm)
500
400
High Gradient
3
2
1
0
4
T2 cutoffs
Partial Porosity
Partial Porosity
4
Low Gradient
0.1
1
100
10
T2 (ms)
Diffusion Effect
Efficiency….Data
accuracy….People-oriented
service
1000
T2 cutoffs
3
2
1
0
0.1
1
100
10
1000
T2 (ms)
No Diffusion Effect
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

NMR Petrophysics
NMR Behavior Of Heavy Oil
Detection Of Heavy Oil – Field Example
Summary
Tar
Clay Bound
Water
Heavy Oil
Capillary Bound
Water
Moveable Water
Water-based
Mud-Filtrate
Incremental Porosity (pu)
T2 Cut-off
0.01
0.1
1
10
100
1000
0.01
0.1
1
10
100
1000
Detected NMR Spectrum
0.01
0.1
1
10
100
1000
T2 (ms)
• What do we know about the model independently
of any NMR data?
Gas
Light oil
Heavy oil
Free water
Capillary-bound
water
Clay-bound
water
◦ T1>=T2,i -> T1/T2,i is used
instead of T1
◦ T1/T2,i < 10 In most cases it
remains under 3.
◦ 0.3 <= T2,i <= 10000 ms
◦ 10-12 <= D <= 10-7 m2/s”
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
NMR Petrophysics
NMR Behavior Of Heavy Oil
Detection Of Heavy Oil – Field Example
Summary
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Located in the heart of
Patagonia, and extending
from the Atlantic Ocean to
the Andean foothills
Accounts for around one
third of the hydrocarbon
production in Argentina.
The origin and subsequent
geological evolution of the
basin are caused by the rift
process responsible for the
opening of the Atlantic
Ocean in early Jurassic
times.
Accumulation of
terrigeneous sediments
continued well into early
Cretaceous times
Lab
Log
Permeability : Timur-Coates
K =  ·  · (BVM/BVI)χ
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

NMR Petrophysics
NMR Behavior Of Heavy Oil
Detection Of Heavy Oil – Field Example
Summary
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In oil-wet reservoirs, T2 intrinsic from water-based
mud filtrate is a very significant indicator of the
presence of movable heavy oil.
The relaxation time of the water-based mud filtrate is
around 1024 ms -a Bulk relaxation phenomenon.
The T2 apparent spectra, when displayed for different
GTE values, reflect mostly the enhanced relaxation of
water-based mud filtrate displacing oil.
The negative slope in depth of the log mean value of
the higher T2 apparent spectral window may also
indicate the presence of heavy oil.
From
Isolated to
Integrated
Data
Analysis
26
Thank you
Obrigado
Gracias

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