Technical Presentations

The controls on the reservoir quality variations of the Habshan Formation located in the north-west of onshore Abu Dhabi, are addressed in this study through an integrated sedimentological, petrographical and reservoir quality assessment. This evaluation is based on core analysis combined with thin-section, SEM, CCA, MICP and wireline log data across 6 wells.

The studied wells are characterized by a wide range of facies deposited within an intertidal environment. These present a wide range of porosity and permeability values, which vary across the reservoir zones. Overall, porosity and permeability increase when passing from mud-supported to grain-supported textures, whereas they decrease with increasing macropore-occluding cementation. The best porosity and permeability values are hosted within floatstones, rudstones and grainstones, as well as dolomitised, micrite-dominated facies. Lateral changes in reservoir quality are observed across the field, with the highest and lowest reservoir potential recorded in the northern and southern wells respectively.

The wide spread of porosity and permeability values is related to the presence of different pore system types, which are the product of the combined action of depositional texture and diagenetic overprint. Well-connected, macropore-dominated networks within grain-supported textures result in high permeability and porosity values, whilst poorly connected, micropore-dominated pore networks within matrix-supported textures produce the lowest. The mixed pore systems comprise a wide range of porosity and permeability values. Mapping these pore types provided an enhanced understanding of the vertical and lateral reservoir quality variability.

This study refines the understanding of the strong link between depositional facies, diagenetic overprint, and reservoir quality distribution in the Habshan Formation, which is poorly detailed in literature. In the field of interest, the southern areas are likely to host reduced reservoir quality due to the intense cementation of the grain-dominated facies, reducing both the macropore volume and pore connectivity. In contrast, enhanced reservoir quality is observed in central and northern areas, where a thicker section of micrite-dominated, more proximal facies are dolomitised, and macropores are less cemented. The established reservoir architecture is a powerful tool to improve reservoir modelling and prediction of sweet spot distribution.

Breislin, C, Galluccio, L, Syofyan, S. and Shabibi, T. A. (2022) Lateral Variability in Reservoir Quality of the Habshan Formation, Onshore Abu Dhabi, UAE. Paper presented at the AAPG Carbonate Sequences and Reservoirs Conference, Naples, 22-23rd Jun, 2022.