Fluid and lithology discrimination of Amangi hydrocarbon field of the Niger Delta using Lambda-Mu-Rho technique

Abstract

Lambda-Mu-Rho analysis was used to identify gas sands of two reservoirs (H1000 and H4000) in Amangi field of the Nigerian Delta. The main objective of this study was to provide a detailedprediction of the properties of these two Tertiary reservoirs using thistechnique of gas sand identification. This was possible because each lithology has a different rock properties response subject to fluid content and mineral properties. The basic impedances of both compressional and shear waves from the angle stacks were determined for the two reservoirs andLambda-Rho (λρ) and Mu-Rho (μρ) calculated. In the gas sand, the low incompressibility(λ) of gas combined with the high rigidity(μ) of sand resulted in a low λρ value, (1.0 x 10 13 kg 2 /m 4 s 2 - 2.0 x 10 13 kg 2 /m 4 s 2 ) and a high μρ response, (1.4 x 10 13 kg 2 /m 4 s 2 - 2.0 x 10 13 kg 2 /m 4 s 2 ). The Vp/Vs ratio ranges 1.6 to1.8 for gas sand and 1.8 to 2.4 for shale. Equipped with this understanding from petrophysics, a high degree of discriminationoflithologies and fluidswas achieved. The gas sands, brine sands and shaleswere characterized successfully by the λρ-μρ space.