Net-To-Gross Ratios: Implications in Integrated Reservoir Management Studies

Abstract

fax 01-972-952-9435. AbstractGeoscientists and reservoir engineers are very well acquainted with the terms "net-to-gross (NTG)" and "petrophysical cut-offs" or just "cut-offs". The significance of these terms is ultimately to define productive zones in the reservoir for hydrocarbon exploitation. However, there has been marked misunderstanding surrounding the usage of the term, net-to-gross and implicitly, the derivation of cut-offs which are limiting values used in expressing the netto-gross ratio. While the geologist may be concerned with the pay for evaluating hydrocarbon-in-place and the ultimately the estimation of economically producible reserves, the simulation engineer is more concerned with fluid flow for pressure support in the reservoir 1 . The significance of this paper is to consider the different cut-offs selection methods, the varying interpretation of net-to-gross ratios and the implications inherent in such methods. A case study from a field in the NigerDelta is also carried out to reveal the impact of such selection criteria especially in rocks with congenital weak hydraulic properties which cannot be excluded at geologic correlation stage 2 . The effect of cut-off parameters on oilinitially-in-place (OIIP) calculation was also investigated and a sensitivity analysis carried out on the petrophysical parameters to reveal the impact of the dynamically conditioned cut-offs selection on the petrofacies. Multiple Monte Carlo realizations were also employed to obtain probabilistic OIIP estimates rather than a single deterministic result.

Stochastic modelling of spatial variability of petrophysical properties in parts of the Niger Delta Basin, southern Nigeria

“…The risk in this technique lies in the changes in recoverability during the life of the field and recovery technique employed (Worthington and Cosentino 2003). Hence, NTG can change during field life, which can be misleading (Egbele et al 2005). NTG was estimated using Eq.…”

Reservoir Characterization of Lower Qamchuqa (Shu'aiba) Formation from the Well BH-86, Bai- Hassan Oil field, Northern Iraq

“…In the same manner and for gas production the permeability cutoff of 0.1 mD considers l. Net to Gross Reservoir and Pay Ratios The significance of the terms "net-to-gross" (NTG) and "cut-offs" is ultimately to define productive zones in the reservoir for hydrocarbon exploitation. The geologist may be concerned with the pay for evaluating hydrocarbon in-place and the ultimate estimation of economically producible reserves [40].…”

Utilização de perfil geofísico de densidade e de imagem de densidade associada a algoritmos de aumento de contraste para estimativa de Net Pay em poços horizontais

“…Autores comoWorthington e Consentino (2003);Egbele et al (2005) eWorthington (2009), entre outros, formularam diferentes rotinas de utilização de perfis para gerar uma classificação de espessuras de intervalo avaliado, associada à real contribuição e ao fluxo de hidrocarbonetos. Em síntese, grande parte dos autores utiliza o V sh para delimitar a espessura de rocha reservatório(Net Reservoir, Net Sand, Gross Sandstone ou Net-to-Gross Sand).…”