ONGC A Bharadwaj

R C P Saxena

S Uppal

CiteSeerX

 
 
 
 
 
 
 
A & AA Basin, ONGC, Jorhat 
Roopesh_saxena2001@yahoo.co.in 
 
 
 P-282 
 
Simultaneous analysis for Dry well and Future prospective location with the 
use of calibrated seismic attributes and newly generated rock property 
volumes – A Case Study 
 
R.C.P.Saxena*, S.Uppal & A.Bharadwaj, ONGC 
 
Summary 
 
The  analysis  of  complex  trace  attributes  with  the  incorporation  of  petrophysical  rock  properties  provide  a 
meaningful explanation  for the lithology prediction.  Moreover, it may also help to identify hydrocarbon bearing sands in 
the clastic environment.  The current paper presents a unique combination of the seismic attributes along with generation of 
the rock property volumes and their blending, which helps us to justify dry well, oil bearing wells and new exploratory 
locations for the oil bearing sands.  The  attributes  discussed  in this  paper  are the outcome  of the work relating  to t he 
combined  use of several  attributes  for lithology  prediction  and reservoir characterization. 
 
 
Introduction 
 
The calibrated seismic attributes with the known 
petro physical properties provides more precise 
information about the lithology and reservoir 
(Cynthiaetal1997). The current study is carried out in  
Panidihing   area   of  Assam   &Assam   Arakan 
Basin,  which falls in the north eastern  part of the 
india   (Fig.1a).The   work   is  carried   out  for   the 
PreBarail  formations  (Sylhet  ,Tura,  Barail ),which 
have   the   proven   oil  wells   in  the  area,   where 
tectonic  plays an important  for the oil entrapment. 
Coherence & sweetness    seismic attributes, along 
with the P impedance & Porosity (using available 
Log data) volumes are generated from 3D seismic. 
Pertinent    combination  of  different  attributes  and 
their  blending  provides  a  meaningful  justification 
for the producing,  dry and prospective  (New) well 
locations. 
 
 
Fig.1 Location map of the area (a) and Geology of upper Assam for 
Pre Barail formations (b). 
 
Brief of Geology of the Area 
 
The basin is primarily a south east dipping  shelf 
over  thrust  by Naga  hills  on  the  south  east    and 
Himalayan mountain range to the north. The 
petroleum system in the Pre Barail are found in the 
rocks of Kopilli/Sylhet and Barails of Eocene – 
Oligocene of Age.   Sylhet represents the platform 
carbonates and Tura represents the clastic rocks of 
shallow marine shales and sandstones (Fig.1b). The 
Reservoir rocks are carbonates of the sylhet 
formation, interbeded sand stones of kopilli 
formation   and   sanstones   of Barail,   Surma   and 
Tipam Groups.  The trapes are primarily anticlines 
and faulted anticlines along with few subtle 
stratigraphic traps. There is also a likelihood of 
 
 
 
 
 
 
 
 
2 
 
 
Simultaneous analysis for Dry well and Future prospective 
location   with the use of calibrated seismic attributes and newly 
generated rock property volumes – A Case Study 
anticlinal traps in the sub thrust.  The area is well 
known for the oil bearing pockets both in Sylhet and 
in Tura. In general the Tura thickness is about 80 to 
100 m and has two sand packs deposited in two 
different environments   (Fig1 (b)).   Moreover, only 
the upper part of Tura sand contains hydrocarbons. 
The accumulation is governed by structural   play   
with   superposition of   different tectonic regime.  It 
is found that curvilinear fault plays an important role 
in the oil entrapment. However,  the  younger  
formations  in the  area  are devoid  of hydrocarbons  
in spite  of the good  fault closures. 
 
Methodology 
 
The synthetic seismogram generation and their 
correlation for few wells in PreBarails formations are   
carried out in the area. Accordingly,   The Horizons 
correlations at Sylhet top, Tura Top and Basement 
top are tracked in the PSTM 3D Seismic volume 
(Fig.2).  All  the  PreBarails  formations  i.e Zone  of  
interest  are  falling  in  Time  window  of 3100 to 
3400 msec of the seismic volume . 
 
Table 1: STATUS OF DIFFERENT WELLS 
 
 
 
The seismic attributes  volumes  for Coherency  and 
Sweetness   are generated from the  seismic volume in the  
time  window  of  3100  to 3400msec.(Fig.3, 4&5).Model  
based seismic data inversion is carried out in the same 
window for the generation of P Impedance volume and 
there after generation of the Porosity volume using Probable 
Neural Network (PNN)  algorithms.(Fig  6  &7).Using  all  
the generated  volumes,  the reservoir  analysis has been 
carried   out   mainly   at   the   pay   sands   and   its 
extension  both in Tura  and Sylhet formations. The results 
are calibrated with the known findings in the Tura and 
Sylhet formations.  Analysis in different combinations of 
attributes has been carried out. 
 
 
Fig.2 An arbitrary  seismic   line passing through different wells and 
new probable locations. 
 
Discussion 
 
Complex Seismic Trace Attributes have gained 
considerable    popularity,    first   as   a   convenient display  
form,  and  later, as they are incorporated with other seismic 
and well log derived measurements,  they became a valid 
analytical tool for lithology prediction and reservoir 
characterization (M. T.Taner2001etal.). 
 
The   coherence   cube   offers   a   high   resolution 
unbiased image of the variations within the volume, 
wherein geologic features and faults are enhanced (Fig.4).It 
helps to identify the zones for 
 
 
Fig.3   An   arbitrary line from   sweetness attribute volume passing   
through   different wells and new probable locations. Dotted circles 
shows the oil producing zones for PD-D&B. Relatively, higher  the 
value shows the distribution of the sand body.  Producing wells fall in 
it, except PD-C, where structure does not support, so found to be dry. 
 
 
 
 
 
 
 
 
3 
 
 
Simultaneous analysis for Dry well and Future prospective 
location   with the use of calibrated seismic attributes and newly 
generated rock property volumes – A Case Study 
 
Fig.4 Arbitrary lines from Coherency attribute volume passing 
through RPD-A,PDA& C(a) and PD-B,D &A(b). It explains the 
pattern of faults e,g curvilinear etc. existing in the zone of interest. 
 
The hydrocarbon entrapment. Sweetness is instantaneous 
amplitude divided by the square root of instantaneous 
frequency (Bruce S. Hart1,Qubec,Canada). It is usually a 
sand shale indicator for siliciclastic environments. Presence 
of hydrocarbon increases the amplitude strength and 
decreases frequency content. Hence, sweetness attribute 
helps to identify the sand body This attribute often helps to 
locate not only successful exploratory wells but also gives 
an idea about the extent of the pool(Fig.3),as marked in the 
dotted circles. An arbitrary line from sweetness with 
coherence volume shows(Fig.5a) , that wells PDB & D are 
producing oil from marked (dotted cirle) yellow colour 
attributes, while the well PDA is dry, does not fall in the 
same colour ,however the  RPD-A  ,falls  in  the  colour  of  
the  producing zones  for  PD  B  &  D,  so  it  could  be  
prospective location  for  the  hydrocarbon  point  of  view,  
since the  structural  and  stratigraphic  features  are  
favourable.  Similarly  well  PD-A  (Fig.5b)  does  not  fall  
in  the  colour  attributes(dotted  circle)  of  the producing  
wells  as  in  PD-B  &D(Fig.5a).So,  Well PD  A  is  found  
to  be  dry.  It  justifies  and  calibrates the  attributes.  
Moreover,  again  well  RPD-A  is found  to  be  favourable  
for  new  location.  Another arbitrary  line  (Fig.5c)  shows  
that  the  well  PD-B &D  falls  in  the  colour(dotted  circle)  
of  the producing  wells,  while  PD-A  does  not  fall  in  the  
colour  of  the  producing  well  i,e    a  dry  well.  The other  
arbitrary  line  (Fig.5d)  passing  through  wells namely  
PD-E  &  C  are  dry  and    not  supported  by the 
attributes(dotted circle) and The other  location i,e  RPD–B  
,which  is  identified  on  the  basis  of  the structural 
location  does not support the attribute of the producing 
well. So, the location RPD-B may be ignored on the basis of 
the attributes analysis.   
 
The inverted seismic volume exhibits an improved image of 
the P-impedance variations, which can be used for 
lithologic and stratigraphic interpretations. (Brian P.  West  
etal.2002)  The  RMS  time slice(Fig.6a)  of  the  P  
impedance  volume  for  Tura top  with    10ms  above  and  
10  ms  below,  i,e  the producing  zone  window  from  the  
Tura  formation shows that the producing wells PD –D(falls 
in fault plane  thus  shows  high  porosity  and  high  P-
Impedance)  &  B  falls  in  same  colours  of impedance  
values  than  those  of  the  dry  wells  ,i,e PD-A & C. 
However, the new prospective location namely  RPD-A  &  
B  do  falls  in  the  impedance values  of  the  producing  
wells.  The  same  P impedance  volume  has  been  taken  
as  input  for  the calculation of Porosity volume in the same 
zone of interest.  The  RMS  time  slice  of  the  porosity 
volume  in  the  same  windows(Fig.6b),justifies  the 
producing  wells  PD-D  &  B  and  one  new  location 
RPD-A,  at  the  same  time  also  justify  the  dry  well 
locations  namely  PD  –A  &C  on  the  basis  of  the values 
of(Low) porosity distribution in the volume. The arbitrary 
line passing through different wells in porosity and 
impedance volumes (Fig.7),shows that producing  wells  are  
having  more  porosity  values (Fig.7a)  and  less  
 
 
 
 
 
 
 
 
4 
 
 
Simultaneous analysis for Dry well and Future prospective 
location   with the use of calibrated seismic attributes and newly 
generated rock property volumes – A Case Study 
impedance  values,for  Tura formation,(Fig.7b).The  well  
log  correlation  (Fig.8) interpret  the  oil  bearing  lithology  
for  Tura formation.It provides a clue for producing and  
non producing  lithology,  as  marked.  The  blending  of the  
Sweetness and  porosity  volume  with  the known 
producing  zones   (in range) values  (i,e  well  locations,  
PD-B,D  and  F)  are  attempted (Fig.9).The  blended    
output attributes  in  map  view shows  that  the  calibrated  
values  at  the  wells  PD-B,D &F, spreads justify the dry 
wells (does not fall on    attributes  cloud)  and  also  justify  
one exploratory  location  RPD-A,  while  discarding  the 
other  RPD-B.  in  the  known  producing   zone  of 
interest,i,e 3100 to 3400ms . 
 
Results 
 
The integration of the coherence and sweetness attribute 
volumes depicts the changes that can be  
 
 
 
 
 
Fig. 5 Arbitrary    lines  from Sweetness attribute overlaid with 
coherency volume passing through PD-B,D&A,RPD-A(a),PD-F 
&A,RPD-A(b), PD- B,D&A(c),PD-E  &C,RPD-B(d).  The marks 
area shows the producing zones. 
 
readily identified  within  sedimentary  systems  for Pre   
Barail   formations   of   the   Panidihing   Area, resulting  in 
unparalleled detail  of subtle sedimentary depositional 
features.   Moreover, Seismic inversion for acoustic 
impedance provides an   easy   and   accurate interpretation    
for the lithologic and stratigraphic identification. The 
generation  of the porosity  volume  using  Probable Neural  
network  (PNN)  alogorithim  with  P impedance volume 
further enhance the quantitative interpretation  confidence.  
As discussed  above,  the convergence  of  all  these  studies  
provides  a more confident    Geological    interpretation  of  
the  area. Which may be simultaneously used   for Dry Well 
analysis and prospective exploratory locations with  
justification.   
 
 
 
 
 
 
 
 
 
5 
 
 
Simultaneous analysis for Dry well and Future prospective 
location   with the use of calibrated seismic attributes and newly 
generated rock property volumes – A Case Study 
 
Fig. 6   RMS   Time   slice   extracted   from  P- Impedance    volume  
(a)   and   from   porosity volume  (b).   
 
 
Fig.7 Arbitrary lines from porosity attribute volume(a)  and (b) P 
Impedance volume passing through different wells in the zone of 
interest. Dotted circles shows the producing zones. 
 
The study can further be used for the calculation of 
reservoir properties like fluid fill and net pay. 
 
Conclusion 
 
The   power   of   the   combined   use   of   multiple 
attributes    has   been recognized    and   a   newtechnique   
has   been introduced   that   produces reliable, quantitative 
results. The conventional seismic  attributes  such  as  
coherence, sweetness, along  with  derived  rock  properties  
like  P impedance and porosity  provides enhanced  ability 
to quantify   and   predict   reservoir   properties between   
sparse well data of Panidihing area. Blended plots of 
derived attributes were used to define precise reservoir and 
 
Fig.  8  Well  Log  correlation  for  the  Tura formation   for the well 
PD-B,D,F,C & A. 
 
 
Fig.  9  Blending  of  attributes  namely  Sweetness and  porosity  
volume  in  the  zone  of  interest  i,e  3100 to 3400 ms with known 
range of producing zones  for  the  well  PD-B,D  &F.  It  justify  dry 
wells  PD-A  &  C  and  prospective  location  RPD-A. 
 
non-reservoir facies boundaries and reservoir   
compartments. This guides in making a logical analysis for 
new exploratory location along with the   reason for the dry 
wells in the zone of interest. It may also help in 
understanding of the sub-surface and may be instrumental 
in reducing risk and uncertainty. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
6 
 
 
Simultaneous analysis for Dry well and Future prospective 
location   with the use of calibrated seismic attributes and newly 
generated rock property volumes – A Case Study 
References 
 
Potential risks when using seismic attributes as predictors of 
reservoir properties,CYNTHIA T. KALKOMEY,  Mobil 
E&P Technical Center, Dallas, Texas, MARCH 1997 THE 
LEADING EDGE 
 
Seismic attributes,their  use in petrophysical classification. 
M. T. TANER, J. WALLS and G. TAYLOR, EAGE 63rd 
Conference  & Technical Exhibition – Amsterdam,  The 
Netherlands,  11 - 15 June 2001 
 
Interactive seismic facies classification using textural 
attributes and neural networks   
 
BRIAN P. WEST, STEVE R. MAY, JOHN E. 
EASTWOOD, and CHRISTINE ROSSEN, ExxonMobil 
Upstream Research Company, Houston, Texas, U.S.,, THE 
LEADING EDGE OCTOBER 2002 
 
Channel detection in 3-D seismic data using sweetness 
attributes Bruce S. Hart1,1 Earth and Planetary Sciences 
Department, McGill University, Montreal, Quebec H3A 
2A7, Canada. 
 
Acknowledgement 
 
The authors sincerely thank the Director (E) & Basin   
Manager, A & A A Basin, ONGC India, for permission   to 
publish   this paper.  The views expressed in   this   paper are 
exclusively those of the authors and need not necessarily   
match with official views of ONGC. 


Simultaneous analysis for Dry well and Future prospective location with the use of calibrated seismic attributes and newly generated rock property volumes -A Case Study

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Simultaneous analysis for Dry well and Future prospective location with the use of calibrated seismic attributes and newly generated rock property volumes -A Case Study

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