AVO analysis & rock physics based AVO inversion Stud. MSc
Asger Johansen Supervisors: Thomas Mejer Hansen, IMM DTU Ida Lykke
Fabricius, BYG DTU 1/46Thesis defence 14/5-2012
Slide 2
Presenting Objectives of the thesis Part I-III Method Results
Conclusions Thesis: Discussion Thesis: Conclusion 2/46Thesis
defence 14/5-2012
Slide 3
3/46 (picture: Schiler et. al) Nini-1 Area of seismic data
Thesis defence 14/5-2012
Slide 4
Objectives 4/46 Investigate and assess the AVO response of
North Sea oil and brine saturated greensand from the Hermod
formation Investigate the possibility of identifying oil reservoirs
from seismic data Investigate the prospects of predicting the
physical properties of greensand from seismic data by a rock
physics based non-linear AVO waveform inversion AVO response AVO
analysis AVO inversion Thesis defence 14/5-2012
Slide 5
Workflow 5/46 AVO response Prospects of inverting seismic data
AVO analysis Where to invert AVO inversion Predicting physical
properties Thesis defence 14/5-2012
Slide 6
Part I: AVO response of greensand Forward model the AVO
response Estimate elastic properties Oil and brine sat. greensand
Of an upper and lower reflecting layer Observe the AVO response
from seismic data 6/46Thesis defence 14/5-2012
Slide 7
7/46 (picture: Kearey, P. (2002) AVO (Amplitude variation with
offset) Thesis defence 14/5-2012
AVO response 11/46 Observed from the seismic data at the
Nini-1a well location Thesis defence 14/5-2012
Slide 12
AVO response From seismic data 12/46Thesis defence
14/5-2012
Slide 13
Conclusion - Part I: AVO response of oil sat. greensand AVO
response of oil sat. greensand different from brine sat. greensand
Oil saturated characterized by: a top reflector which amplitude
increases negatively with offset A bottom reflector which amplitude
increases positively with offset 13/46Thesis defence 14/5-2012
Slide 14
Part II: Identifying possible oil reservoirs Method of
identifying the seismic attribute of oil Visualize the possible oil
reservoirs 14/46Thesis defence 14/5-2012
Slide 15
15/46 B (slope) 0 B (slope)= big negative A A Thesis defence
14/5-2012
Conclusions from part II Method of identifying possible oil
reservoirs verified The oil reservoir around Nini-1a and Nini-4
identified Another known oil reservoir identified A third possible
oil reservoir identified 26/46Thesis defence 14/5-2012
Slide 27
Part III: AVO inversion Predicting physical properties of
greensand from seismic data non-linear AVO waveform inversion
Metropolis inversion 27/46Thesis defence 14/5-2012
Slide 28
Principle of the algorithm Iteratively Sampling a realization
of the posterior distribution 28/46 Propose model Forward model
Misfit to data Accept / reject model Thesis defence 14/5-2012
Slide 29
Forward model Non-linear rock physics model Non-linear
reflectivity model Convolution model 29/46Thesis defence
14/5-2012
Slide 30
The rock physics model Hertz-Mindlin grain contact model
Modelling: K dry and Estimating: Poisson ratio Glauconite bulk and
shear moduli Gassmann fluid substitution Estimating: Mineral
modulus 30/46Thesis defence 14/5-2012
Slide 31
Illustrate forward model 31/46Thesis defence 14/5-2012
Slide 32
Sampling a posterior distribution Accept model by: Likelihood
of a proposed model Accept: If: L(m_propose) >= L(m_current)
Else if: L(m_proposed) / L(m_current) > rand([0:1]) m_current =
m_propose Measure of how well the accepted models fits data
relative to each other Number of iterations between accepted models
SPE meeting 28/2-201232/46
Synthetic reference model Different prior scenarios The
waveform inversion requires the elastic properties of the 1. and /
or 3. layer to be known Inversion using the Hertz-Mindlin rock
physics model is found to require the P eff, C and glauconite to be
known 34/46Thesis defence 14/5-2012
Slide 35
Inverting seismic data 35/46 = 0.25 glau = 0.4 F glau = 0.3
C=15 P eff = 22 MPa Oil sat = 0.9 Thesis defence 14/5-2012
Modeling greensand Estimating the: Mineral modulus Poisson
ratio Glauconite bulk and shear moduli Investigating these
estimates by inversion of seismic data The estimates proposed by
Zakir Hossain are verified from seismic data 41/46Thesis defence
14/5-2012
Slide 42
Inverting seismic data Nini-1a A discrepancy observed Seismic
data Forward model Elastic properties above the greensand Inversion
by a 3-layer model 42/46Thesis defence 14/5-2012
Slide 43
Conclusion part III Feasible to invert the physical properties
of greensand from seismic data Requires prior information on both
the greensand and the elastic properties above and/ or below
Challenge describing the seismic data by a 3- layer model
43/46Thesis defence 14/5-2012
Slide 44
Discussion Thesis: The assessed AVO response depends on the
geological setting The method of identifying possible oil
reservoirs only indicates a possible seismic anomaly Challenge of
inverting seismic data at locations without information from a well
log Describing the seismic data by a 3-layer model 44/46Thesis
defence 14/5-2012
Slide 45
Conclusion Thesis: The results of part I supported: the
possibility of identifying possible oil reservoirs from seismic
data by AVO analysis An the possibility of inverting physical
properties of greensand by AVO inversion Two possible oil
reservoirs identified Inversion of physical properties are feasible
however a challenge is encountered Thesis defence
14/5-201245/46
Slide 46
Conclusion Thesis: Elastic properties and the physical
properties of greensand are required to be known Inverting the
physical properties at the two unknown possible reservoirs was not
possible 46/46Thesis defence 14/5-2012