Diagenesis Study of the Thamama Zone-A, Asab Field, UAE

Abstract

This study aims to investigate the diagenetic processes and their products of the Asab Field Lower Cretaceous Thamama Zone A. The thesis It discusses the main diagenetic processes and their impact on reservoir quality, and it analyzes the evolution of the diagenetic fluids that participated in these diagenetic processes. The study pays special attention to the existence of fractures and their involvement in the diagenesis process and therefore their effect on the reservoir quality. The study is conducted based on the analysis of four cored wells from different locations (crest, mid-flank and flank) using petrography, SEM, cathodoluminecsnce, fluorescence, fluid inclusions, stable isotopes, strontium isotopes and major, trace and rare-earth element geochemistry. Cementation is the main diagenetic event observed and calcite cement occludes fractures and fossils molds. Other diagenetic processes are microbial micritization, recrystallization, dissolution, compaction and—to lesser extent—fracturing. Fracturing did not enhance the porosity and permeability of the reservoir zones. The same situation applies for dissolution, while cementation has negatively affected the reservoir porosity and permeability. Isotopic and geochemical analyses demonstrated that the fluids that formed the cement were evolved in reducing environment; as demonstrated by high iron concentrations, bright luminescent sparry calcite cement, the formation of Framboidal pyrite, and the negative Ce anomaly. The porosity and permeability values vary in Asab field depending on the sample locations; where the best porosity and permeability values (the best reservoir quality) lay in the crest of the field and their values decrease as we move to the flanks. The diagenetic processes show certain trends; where the dissolution is trending NE and the sparite cementation is trending SN. Good understanding of these trends can help in applying improved reservoir development plan.

Date of Award	Jan 2013
Original language	American English
Supervisor	Ihsan Shakir Al Aasm (Supervisor)