Fluid prediction using AVO analysis and forward modelling of deep reservoirs in Faith Field, Niger Delta, Nigeria
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Date
2015
Authors
Adeoti, L
Adeleye, K.O
Itsemode, A
Bello, M.A
Journal Title
Journal ISSN
Volume Title
Publisher
Arabian Journal of Geosciences
Abstract
Amplitude versus offset AVO analysis and forward
modelling were used to predict the fluid type and seismic
signature in a deep gas reservoir in faith field, Niger Delta.
Well A, which identified the major deeper gas bearing reservoir
in this field, was used in the modelling to predict what the
seismic response would be away from this well at varying
thickness and porosity ranges. The entire well was blocked
into alternate layers of sand and shale lithotypes; the sands
were fluid substituted from its initial in situ condition to 100 %
brine saturation, and from the brine case, fluid substituted to
100 % oil and 100 % gas saturations. The elastic properties of
these fluid substituted sands were estimated using the
Gassmann equations and Batzle and Wang. The results were
used in AVO analysis. Seismic forward modelling to determine
the seismic wiggle signatures of these sands were also
conducted. The variations of pertinent rock properties with
depth of burial were also investigated. The results show that
sand alpha (interval 10,400–10,650 ft) exhibited a typical
class 3 AVO signature. Seismic wiggle response from top of
this sand shows a distinct negative trough on the near angle
stack and a much larger trough on the far stack. Sand beta
(interval 11,700–12,050 ft) exhibited a typical class 2n AVO
signature. Sand wedge model response shows increasing amplitudes
from tops and bases of these sands as a function of
thickness with the limits of seismic resolution shown by the
tuning thickness. The gradient-stack plots, Hiltermann’s
acoustic impedance (HAI) versus Poisson’s ratio (PR) plots
and the AVO models suggest that the hydrocarbon-bearing
sands will be distinguishable from sands with 100 % brine
saturations. There is significant overlap between oil and gas
plots because the oil was modelled as having a high gas oil
ratio (GOR) of 3,586. The reservoirs at this level in Faith Field
are either condensate or gas bearing. Seismic direct hydrocarbon
indicator (DHI) and lithologic delineation are better defined
in the shallower sand alpha than the deeper sand beta.
These models have shown that any good quality seismic
acquired over this prospect would be useful in deriving reservoir
properties from seismic (RPFS) for these reservoirs and
would be effective in lithologic differentiation or hydrocarbon
identification.
Description
Keywords
AVO analysis , Forward modelling , Sand alpha , Sand beta
Citation
Itsemode, A., & Bello, M. A. Lukumon Adeoti, Kolade O. Adeleye (2015). Fluid prediction using AVO analysis and forward modelling of deep reservoirs in Faith Field, Niger Delta, Nigeria. Arabian Journal of Geosciences, 8, 4057–4074