English abstract
The Lower Shuaiba Formation is one of the complex carbonate reservoirs in the
Middle East that are characterized by extensive textural heterogeneity that corresponds
to highly variable reservoir properties. This heterogeneity is related to discrepant
depositional settings during the Shuaiba deposition and the digenesis, which had a
severe overprint on the original properties. Facies mapping is important to unlock the
uncertainties of facies distribution and characterization, highlighting the extent of good
quality facies within the reservoir. The key objectives of this study are to capture the
lateral distribution of reservoir properties within the Lower Shuaiba in the Musallim
Field by identifying facies types and mapping their spatial distribution.
The approach used in this study involved a specific workflow that implemented
many datasets to capture reservoir heterogeneity and develop a facies model for the
Lower Shuaiba in the field. Geological, seismic, petrophysical, well, dynamic, drilling
data, and microfacies analysis are all included in the dataset. This work contains a
detailed methodology of reservoir rock typing application that is used for predicting the
reservoir characteristics of uncored intervals by integrating petrophysics and
sedimentology. The final developed maps and models represent the reservoir's internal
architecture, highlighting the different expected facies types, their trends, and the
expected reservoir quality.
The abundance of the Algal-rich characterizes the reservoir in the field area and
represents the dominated facies, which cover most of the topmost 10-20 m of the
reservoir. The regional depositional setting for the field is a shallow lagoon with
restricted open marine input caused by penecontemporaneous buildups. Reservoir
quality is primarily governed by diagenesis, not only by facies types. The abundance and
arrangement of lithofacies rich in large skeletal allochems, such as the Algal-rich and
Rudist-rich dominated lithofacies, play a pivotal role. Dissolution enhancement in these
lithofacies fosters more effective connectivity among pores, distinctly surpassing the
pore network of the Wackestone-dominated lithofacies. Most connected pores are
interpreted as being created by the acidic, aqueous, unsaturated fluids that preceded/or
came with hydrocarbon charge time. Depositional heterogeneities, subsequent diagenetic
modifications, and structural adjustments have controlled the development and
distribution of lateral reservoir properties.
