Late Pliocene Sapphire Sand Reservoirs Characterization Using Nuclear Magnetic Resonance: Sapphire-1 well, Case Study, WDDM, Egypt

Abstract

This paper documents first deployment of new Magnetic Resonance (NMR) approach for characterizing late-Pliocene complex shaly sandstone reservoirs Sapphire field. Use of conventional logs like Gamma ray, Density, Neutron and Sonic for the reservoir characterization in these reservoirs pose challenges due to its lithological complexity and hetrogenity. The Pliocene delta slope-channel play (Sapphire Field) reservoirs are a shaly sandstone reservoir with vertical and lateral heterogeneous properties. The clay content in such reservoirs causes overestimation of the shale volume and overestimation of the formation porosity leading to inaccurate identification of lithology and estimation of the formation fluids using the conventional logs. Therefore, the porosity independent lithology Magnetic Resonance logging measurement was acquired in dual-wait time enabled T2 polarization mode to differentiate between moveable water and hydrocarbons. After acquisition, standard deliverables were porosity and permeability index with the porosity divided into clay-bound water (CBW), bulk-volume irreducible (BVI) and bulk-volume moveable (BVM) components. The rock quality was interpreted based using permeability index and effective porosity ratio, and classified based on its gradients, to identify the high, medium to low, and tight flow unit zones. The steeper ratio gradient was interpreted as high flow, gentle gradient as medium to low flow and flat gradient as tight flow zones. Based on the NMR flow units and fluid types (CBW, BVI and BVM), the drilled interval was classified into ten compartments of high flow, eleven compartment of medium to low flow along with three tight compartments. The relationship between storage and flow capacities for these compartment intervals revealed that, whereas the high flow units only have 19 % of the total storage capacity, they contribute over 70% of the total flow capacity, while the medium to low flow units containing 71% of the total storage deliver 29% of the total flow capacity, finally the tight flow units have 10 % of the total storage and 1 % of the total flow.