An integrated sedimentological, rock typing, image logs, and artificial neural networks analysis for reservoir quality assessment of the heterogeneous fluvial-deltaic Messinian Abu Madi reservoirs, Salma field, onshore East Nile Delta, Egypt

Abstract

This study introduces an integrated evaluation of geological and geophysical data, including sedimentology, diagenetic alteration, image log analysis, core measurements, formation evaluation, and a neural analysis technique (K-mode algorithm) to characterize the upper Messinian heterogeneous reservoirs of the Salma Field, Nile Delta, Egypt. It links observed reservoir permeability and flow zone indicators (FZI) to predict reservoir quality and distribution within un-cored parts of the field. Core and image log analysis show that the Abu Madi sandstone reservoir is composed of seven clastic litho-facies deposited within fluvial to deltaic environments. The reservoir is controlled by four hydraulic flow units (HFU's) and five flow units (FU). Fluvial channel facies, tidally influenced fluvial channel facies, and uppermost parts of bayhead delta facies are dominated by clean sandstone with a low clay content (avg. 20%). These facies are characterized by the high pore-throat sizes (R35 and FZI values), indicating a pore system dominated by mega-to macro-pores. The estuarine facies is composed of mudstone, siltstone, and argillaceous sandstone, with 25% average clay content and moderate R35 and FZI values, indicating a pore system dominated by macro-to meso-pores. The heterolithic estuarine and bayhead delta facies contain abundant argillaceous-rich sandstones, with 29% average clay content and low R35 and FZI values, indicating a pore system dominated by micro-pores. A neural log technique was applied to predict FZIs and permeability in un-cored intervals. Paleocurrent analysis was conducted using image log data to guide sweet spot and reservoir quality tracking across the field. Reservoir quality is controlled by both diagenetic and depositional processes, chiefly an abundance of detrital clays, grain size, and sorting. In the Salama Field reservoirs, mineral dissolution, cement dissolution, and micro-fractures enhance the pore system, while pore-filling and grain-coating detrital clays reduce reservoir quality. These results are important as they improve the wider understanding of the Messinian Abu Madi reservoir in the wider Mediterranean region.