This study used elastic impedance inversion and pre-stack attribute analysis on 3D seismic data with limited well control to identify productive zones in an offshore Iranian reservoir. Poisson dampening factor and Lame parameters extracted from pre-stack simultaneous inversion effectively delineated hydrocarbon-bearing areas, validated by crossplots of elastic impedance volumes. The attribute analysis results at well locations were generalized to the full seismic volume since the reservoir was considered laterally homogeneous.

1. 75th
EAGE Conference & Exhibition incorporating SPE EUROPEC 2013
London, UK, 10-13 June 2013
Tu P11 08
The Application of Elastic Impedance Inversion
and Pre-stack Attribute Analysis for Prospect
Identification - A Case Study
H. Karbalaali (Petroleum University of Technology), S.R. Shadizadeh
(Petroleum University of Technology), M.A. Riahi (University of Tehran) &
S.H. Karimi* (University of Newcastle)
SUMMARY
In this study, with limited well control and pre-Stack Time Migrated (PSTM) seismic data, the advantage
of performing Elastic Impedance Inversion is investigated for an offshore sandstone reservoir, south of
Iran. Pre-stack simultaneous inversion is also applied in order to extract several pre-stack seismic
attributes including: Lame parameters, Poisson Impedance and Poisson Dampening Factor. The attribute
analysis at the well location is studied to find the best fluid-sensitive factors for delineation of hydrocarbon
bearing zone of the reservoir. The result of the analysis at the well location is generalized to the volume of
study since the reservoir under study is considered as a homogenous layer without any complicating
factors of sealing faults, secondary porosity and lateral change of lithology.

2. 75th
EAGE Conference & Exhibition incorporating SPE EUROPEC 2013
London, UK, 10-13 June 2013
Introduction
Reservoir characterization plays an important role in different parts of an industrial project. The
results from a reservoir characterization study gives insight into rock and fluid properties which can
optimize the choice of drilling locations and reduce risk and uncertainty. Delineating hydrocarbon
bearing zones within the reservoir is the main objective of any seismic reservoir characterization
study. In the current study with PSTM seismic data and limited well control, an attempt was made to
predict the productive zone of the reservoir using Elastic Impedance Inversion, pre-stack simultaneous
inversion and attribute analysis. The focus of this paper is on the application of elastic impedance
inversion, Poisson Dampening Factor (PDF) and lame parameter of incompressibility to discriminate
productive zone of the reservoir. However, like all seismic derived approaches, this technique is not
one of a kind and needs to be validated with other types of data.
The current study is on a southern Iranian offshore oilfield. The field is a NW-SE trending anticline
dipping by 1-1.5 degrees. Hydrocarbon is produced from the Oligocene-Miocene formation having a
vertical closure of 62 meters. The reservoir consists of three units: Upper carbonate, target sandstone
and Lower carbonate. The target reservoir in this study consists dominantly of sandstone with
interbedded dolomite and shale.
Elastic Impedance Inversion
Connolly (1999) claimed that it is possible to process 3D data sets as partial offset/angle stacks. He
asserted that the amplitudes of far-offset stack data can be tied to well logs using synthetics based on a
function called elastic impedance (EI) which is similar in nature to acoustic impedance. EI is defined
as follows:
EI(θ)= VP
(1+tan2θ)
. Vs
(-8ksin2θ)
.ρ(1-4ksin2θ)
Figure 1, which is the crossplot of elastic impedance at 35 versus P-Impedance, confirms the
advantage of elastic impedance inversion respect to conventional post-stack inversion in the current
study for delineating hydrocarbon bearing zone of the reservoir. The analysis for obtaining proper
angle range for generating partial angle stacks of seismic data revealed two appropriate ranges one for
angles between 0-28 and the other for angle range of 28-42 degrees. Model-based post-stack seismic
inversion was performed on these partial stacks to obtain elastic impedance at near- and far-angles of
incidence.
Pre-stack simultaneous Inversion
Pre-stack simultaneous inversion introduced by Hampson et al. (2005) can be thought of as a
generalization of post-stack seismic inversion into pre-stack domain. P-Impedance, S-Impedance and
density can be simultaneously outputted from the inversion result. However, in the current study, the
angle range at the horizon of interest does not exceed 45 degrees, so density cannot be estimated
reliably. Lame parameter of incompressibility (λ) which is obtained from pre-stack seismic data is an
efficient attribute for discriminating fluid. Poisson Impedance (PI) is a new attribute which was
introduced by Quakenbush et al., (2006) as follows:
Mazumdar (2007) extended the work of Quakenbush et al. and introduced a new attribute called
Poisson Dampening Factor (PDF) which is related to Poisson Impedance and Poisson ratio ( ) as
follows:
PDF* PI.

3. 75th
EAGE Conference & Exhibition incorporating SPE EUROPEC 2013
London, UK, 10-13 June 2013
Sensitive attribute analysis
Crossplot analysis has been made in the well location to find the sensitive factors for delineating the
productive zone within the reservoir. Figure 2 illustrates the crossplot of PDF versus Poisson
Impedance at the well location. PI, inherently, has the advantage of discriminating hydrocarbon
bearing zone much stronger than AI and SI. As it is clear from the Figure 2, PDF is more robust in
distinguishing the productive zone of the reservoir respect to Poisson Impedance in this study. A
section of PDF derived from pre-stack seismic inversion is shown in Figure 3. Note the possible
productive zone is highlighted as a zone of high PDF. Figure 4 displays the section of
incompressibility which is consistent with the PDF result in delineating the hydrocarbon bearing zone
of the reservoir. Figure 5 illustrates the crossplot of elastic impedance at near angle of incidence, i.e.,
14 degrees versus elastic impedance at far angle of incidence, i.e., 35 degrees at the well location. The
colour key is water saturation. Figure 6 demonstrates a crossplot of Lambda-Rho versus Mu-Rho in
which the third dimension is water saturation. Note the Hydrocarbon bearing sandstones are
delineated as a zone of low incompressibility and rigidity. Figure 7 displays the crossplot of elastic
impedance of near-angle stack seismic volume versus elastic impedance of far-angle stack seismic
volume. The hydrocarbon bearing sandstones are defined as a square in the figure according to the
result at the well location. Figure 8 shows the cross section of seismic volume at inline 250 at which
the predicted hydrocarbon bearing sandstones are depicted. Figure 9 is a crossplot of Lambda-Rho
volume versus Mu-Rho volume in which hydrocarbon bearing sandstones are highlighted as a blue
square due to the analysis result at the well location. Figure 10 displays the predicted hydrocarbon
bearing sandstones at inline 250. Note the consistency of the attribute analysis outputs of elastic
impedance and pre-stack inversions.
Figure 1 Crossplot of EI_35 ͦ vs.P-Impedance Figure 2 Crossplot of PDF vs.PI at at the well
at the well location. location.
Figure 3 PDF attribute section. Figure 4 λρ attribute section.

4. 75th
EAGE Conference & Exhibition incorporating SPE EUROPEC 2013
London, UK, 10-13 June 2013
Figure 5 Crossplot of EI_14 ͦ vs. EI_35 ͦ at the Figure 6 Crossplot of λρ vs. µρ at the well
well location. location.
Figure 7 Crossplot of inverted EI_near vs. Figure 8The hydrocarbon bearing zone shown on
inverted EI_far. seismic section.
Figure 9 Crossplot of λρ volume vs. µρ Figure 10The hydrocarbon bearing zone shown on
volume. seismic section.

5. 75th
EAGE Conference & Exhibition incorporating SPE EUROPEC 2013
London, UK, 10-13 June 2013
Conclusion
1. Crossplot analysis of inverted elastic impedance volumes at near and far incidence angle
provided a means of discriminating productive zone of the reservoir.
2. Examining several pre-stack seismic attributes including LMR parameters, Poisson
Impedance and Poisson Dampening Factor revealed that PDF and incompressibility (λρ) are
the best fluid-sensitive attributes for delineating producing zone within the reservoir.
3. The result of LMR crossplot analysis for delineating hydrocarbon bearing zone of the
reservoir was consistent with the elastic impedance inversion result.
4. The attribute analysis at the well location was generalized to the whole seismic volume to
obtain a reconnaissance view to the whole volume of study for exploration and developing
plans. Although this procedure may accompany some level of uncertainty in heterogeneous
reservoirs, the reservoir under study is considered as a homogeneous reservoir without any
complicating factors of sealing faults, secondary porosity and lateral change of lithology.
Therefore, it is possible to apply the result at the well location to the whole volume of study
without any other geological control available.
Acknowledgment
The authors like to express gratitude to NIOC, Exploration Directorate, particularly Mr. Sokooti and
Mr. Khoshdel for providing the technical support for this study.
References
Connolly, P. [1999] Elastic Impedance. The Leading Edge, 438-452.
Goodway, B., Chen, T. and Downton, J. [1997] Improved AVO fluid detection and lithology
discrimination using Lame petrophysical parameters. 67th
SEG International Annual Meeting, Denver.
Hampson, D.P., Russell, B.H. and Bankhead, B. [2005] Simultaneous inversion of pre-stack seismic
data. Ann. Mtg. Abstracts, SEG, 1633-1637.
Mazumdar, P. [2007] Poisson Dampening Factor. TLE, July 2007, 850-852.
Quakenbush, M., Shang, B. and Tuttle, C. [2006] Poisson Impedance. TLE, spring 2006, 128-138.