Using lame’s petrophysical parameters for fluid detection and lithology determination in parts of Niger delta

CC Ezeh

doi:10.4314/gjgs.v13i1.4

Abstract

This study analyzed seismic and well log data in an attempt to interpret relationship between rock properties and acoustic impedance and to construct amplitude versus offset (AVO) models. The objective was to study sand properties and predict potential AVO classification. Logs of Briga 84 well provided compressional and shear velocities. AVO synthetic gather models were created using various gas/brine/oil substitutions. The Fluid Replacement Modeling predicted Class 3 AVO responses from gas sands. Log calibrated Lambda Mu Rho (LMR) inversion provided a quantitative extraction of rock properties to clearly determine lithology and fluids. Beyond the standard LMR cross-plotting that isolated gas sand clusters in the log, an improved separation of high porosity sands from shale was also achieved using λρ - µρ vs. AI. When applied to the calibrated AVO/LMR attributes inverted from 3D seismic, the λρ analysis permitted a better isolation of prospective hydrocarbon zones than standard AI inversion Thus, as an exploration tool for hydrocarbon accumulation, the Lambda Mu Rho (λµρ) technique is a good indicator of the presence of low impedance sands encased in shales which are good gas reservoirs. KEYWORDS : Impedance, synthetic gather, cross-plotting, porosity, inversion

Highlights

The study area is situated in the eastern coastal swamp region of the Niger Delta in Nigeria (Fig.1)
The motivation for Lambda Mu Rho (LMR) (λ μ ρ) analysis in the study area stems from the failure of the conventional logs to discriminate fluids in the highly porous reservoir sands at depths below 3350m
Levels B1, B2, and B3 Relatively low LambdaRho values were observed in porous gas sands

Summary

Introduction

The study area is situated in the eastern coastal swamp region of the Niger Delta in Nigeria (Fig.). The regional field structure comprises of large collapsed crest rollover anticline trending east – west and bounded to the north by the central swamp II depobelt. The motivation for LMR (λ μ ρ) analysis in the study area stems from the failure of the conventional logs to discriminate fluids in the highly porous reservoir sands at depths below 3350m. The conversion of velocity measurements to Lamé’s moduli parameters of rigidity (μ) and “incompressibility” (λ) offers new understanding into the original rock properties. The Lamé’sparameters μ, λ, and ρ, which represent “incompressibility”, rigidity, and density respectively, allow for enhanced identification of reservoir zones

Methods

Results

Conclusion