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Integration of Well and 3D Seismic data for Prospect Evaluation
A case studyR J Singh* H L Kharoo*, P. Saha* S.N.Singh* & M. Chandra*
Introduction
Following the discovery of oil during
1958 in Cambay Basin, India the exploration
activities were intensified with major thrust to
tap structural prospects. Later, in the early 80s
the potential of subtle traps was realized in search
of finding more hydrocarbons in this basin. As a
consequence, a number of stratigraphic prospects
were discovered . The prospect discussed here is
one of them. Multiple pay reservoirs were found
in Kalol Formation ,but at the same time the geo-
logical complexities of facies development and
hydrocarbon entrapment mode ftrere also under-
stood. 3D survey was carried out to solve such a
problem of the X prospect in Cambay Basin over
which a number of wells were drilled but delin-
eation/development schemes to tap hydrocarbons
of the area are yet to be Finalised. The authors
evaluated 3D seismic data and found that the in-
tegration of geological data with 3D seismic may
lead to solve some of the problems of identify-ing facies and structural details.
Geology
The study area approximately seventy sq.
kms. is a prospect in north Cambay Basin. The
tectonics of Cambay Basin is very well docu-
mented dividing the basin into Mehsana,
Ahmedabad, Tarapur, Broach &Narmada blocks
separated by discrete cross trends (Fig. 1). Theclastic reservoirs within Middle Eocene account
for the major accumulation of hydrocarbons. The
entrapment established is structural, stratigraphic,
and of a combination type. The Eocene sequence
is characterised by three significant rapid trans-
gressive cycles during early Middle Eocene,
Middle Eocene, and Late Eocene with interven-
ing regressive cycles During regression, the ba-
sin fills are characterised by deltaic,backshore-
marshy lagoonal, and fluvial deposits.Lithostratigraphy of the area is shown in Fig.2.
Fig 1: Tectonic Map of Cambay Basin
Data Analysis
Methodology
Fortyeight fold 3D seismic data(bin size 15X75mts.) was acquired over the prospect in 1995 and
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unitwise brief discussion is given below.
K-X unit
K-X silt/sand reservoirs are developed with lim-
ited areal extent and smaller thickness below K-
X coal unit. A NW-SE channel is envisaged (Fig.
13b) based on the effective sand isolith and am-
plitude attribute map derived from seismic data.
K-IX unit
K-IX reservoir with sands or silty facies under-
lying the thick continuous coal unit is better de-
veloped in the area. These reservoirs are also oflenticular nature having limited areal extent and
preferred orientation. Seismic attributes were
analysed to identify the areas of facies develop
ment. For identification of facies both amplitude
and frequency attributes (Fig. 10 & II) were used
and the alignments brought out from these at-tributes were integrated with well data,especially
the effective sand isolith (Fig.l3a). A NW-SE
channel configuration is envisaged. The three
inlets of channels flowing from NW-SE are coa-
lescing around the well X-17 where the thick-
ness of sand is found to be more.
K-VI+VII unit
K-VI+VII reservoir facies is locally developed.
A channel(Fig.l4) is interpreted clubbing botheffective sand isolith map and seismic
data(Fig.l2)
Fig 4: Seismic calibration with Synthetic Seismograph (X-12)
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Fig 10. Sum of Negative amplitude within the time
window where K-IX reservoir is likely to be
present(Thich Horizon seiscrop)
Fig 11. Frequency attribute within a time window where
K-IX reservoir islikely to be present(Thick horizon
seiscrop)
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Fig 12: Sum of Negative amplitudes within atime window where K-VI+VII reservoir is
likely to be present(Thick horizon seiscorp)
Conclusions
Time and depth structure maps bring out
the structural details corresponding to the hydro-
carbon bearing stratigraphic units. K-X and K-
IX top units are represented by coals. K-IX coal
is thick and widely present whereas K-X coal is
Fig 14: Envisaged Geological model for K-VI
+ VII reservoir
Fig 13: Envisaged Geological model for (a) K-IX and (b) K-X reservoir
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relatively thin and pinches out. The pinch out boundary is identified from seismic data. Based on
seismic attributes and well data, different channels are mapped which are the likely areas for delin-
eation/development drilling in the area.
Acknowledgement
The authors are thankful to Mr.A.G Pramanik; Head, GEOPIC and Mr. S.N.Badola, HeadINTEG for their constant guidance and encouragement during the course of work and preparation
of this paper. The authors are also thankful to ONGG for giving permission to publish this paper.