Reservoir Characterization and Geological Modeling of a Lower Cretaceous Reservoir, Offshore Abu Dhabi. Integrating Multiscale Data From Seismic Reservoir Studies and Sedimentological Core Descriptions

Abstract

Reservoir characterization plays a fundamental part in the development and/or appraisal of any hydrocarbon field. Understanding and quantifying the characteristics and distribution of the reservoir rock properties is an evaluation step that needs to be performed before starting any reservoir model. An accurate description of the reservoir is vital to help appropriately manage and optimize oil recovery. From core to seismic scale, any relevant piece of information should be integrated in order to reduce uncertainties, and optimize the understanding of the final flow behaviour and fluid distribution inside the reservoir. This paper presents a detailed and integrated methodology and case study for building a 3D geological model to characterize a Lower Cretaceous reservoir for a field located offshore Abu Dhabi. During this study, data sets from two cored and seven uncored wells were utilized for sedimentological interpretations and sequence stratigraphic analysis to establish a consistent high-resolution sequence stratigraphic framework. The detailed descriptions were linked to the petrophysical properties derived from the conventional core analysis (CCAL) and mercury injection capillary pressure (MICP), developing a new reservoir rock type classification (RRT). Several hydraulic flow units (HFU) were identified and used to evaluate which intervals are the major flow contributors. The identification of these HFUs offers a link between the fluid flow, geological framework and RRTs. From achieving a deep understanding of the depositional facies, their stacking relationships and the reservoir properties in core, these interpretations have been extrapolated into the uncored wells based on specific log responses and following a stratigraphically developed geological conceptual model. Several depositional environment maps were generated for each high-resolution stratigraphic sequence and were used as a guideline for the depositional facies modelling. The objective is to reproduce, within the modelling grid, the depositional and diagenetic characteristics of the sediments, including the petrophysical behaviour, as captured by the integrated rock-type classification. Good-quality 3D seismic data was used to enhance the characterization of the reservoir in the interwell areas by improving the spatial prediction of petrophysical properties achieved during the stochastic seismic inversion. Seismically derived 3D porosity realizations were generated using a geostatistical approach and then used as a secondary variable to guide porosity distribution on the final 3D geological model.

AAPG Datapages/Search and Discovery Article #90370 ©2020 AAPG Middle East Region Geoscience Technology Workshop, 3rd Edition Carbonate Reservoirs of the Middle East, Abu Dhabi, UAE, January 28-29, 2020