Lithology and fluid prediction from simultaneous seismic inversion over Sandfish field, Niger Delta, Nigeria
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Date
2017
Authors
Adeoti, L
Adesanya, O.Y
Oyedele, K.F
Afinotan, I.P
Adekanle, A
Journal Title
Journal ISSN
Volume Title
Publisher
Geosciences Journal
Abstract
Seismic inversion has been widely practiced in the oil and gas industry because it generates broad bandwidth of
impedance data which maximizes vertical resolution and minimizes tuning effects. The lack of accurate prediction of lithology and
fluid content of subtle features identified in seismic data acquired over the Sandfish field, Niger Delta, Nigeria necessitated the use of
seismic inversion. In this paper, simultaneous seismic inversion is adopted to integrate seismic and well data for quantitative
interpretation and uncertainty assessment of the subsurface reservoirs in the Sandfish field. Three Sandfish (Sfn) wells with the
required petrophysical logs, check-shot data, high quality 3D seismic data of five angle stacks (6–12°, 12–18°, 18–26°, 26–32°, and 32–
42°) were used for the analysis. A feasibility study including cross-plots of petrophysical and elastic properties from well data was first
carried out to establish rock property relationships in the interval of interest. Biot-Gassmann fluid substitution analysis was also used
to reveal sensitivity of rock properties to pore-fill type. Low frequency (0–2 Hz) models were generated from interpolation of highcut-filtered
P-sonic, S-sonic, and density logs guided by interpreted seismic horizons. The low frequency models were used to broaden
the spectrum to estimate elastic volumes. The five partial angle stacks were simultaneously inverted using Jason’s Rock-Trace® inversion
software which iterated trial inversions until the model sufficiently matched the seismic data. The inverted P-impedance (ZP), Simpedance
(ZS), and density (ρ) were used to derive Poisson’s ratio (σ), volume of sand (Vsand), lambda-rho (λρ), and mu-rho (μρ).
The cross-plot of λρ with μρ from well data looks similar to that from inverted results. Sands and shales are discriminated on the basis
of sands having low values of μρ. Hydrocarbon-bearing sands are differentiated from water-bearing sands and shales on the basis of
having lowest values of λρ. The Biot-Gassmann fluid substitution analysis at reservoir N-01 reveals typical class III amplitude variation
with angle (AVA) responses for low-impedance hydrocarbon sands. The lithology and fluid prediction maps extracted from Vsand and σ at the
N-01 seismic horizon show variation in lithology and fluid types for the entire volume. The inversion products reveal heterogeneities in the
reservoirs away from well control validated by a blind well test. Hence, the study shows that rock-property model from a simultaneous
inversion is an effective predictive tool for lithology and fluid types which in turn can guide well placement and predict reservoir development
in the field of study.
Description
Keywords
elastic properties , simultaneous inversion , low frequency models , reservoir development , lambda-rho , mu-rho
Citation
Adeoti, L., Adesanya, O. Y., Oyedele, K. F., Afinotan, I. P., & Adekanle, A. (2017). Lithology and fluid prediction from simultaneous seismic inversion over Sandfish field, Niger Delta, Nigeria. Geosciences Journal, 10, 1-15.