--> Insights on Characterization of a Shallow, Restricted Carbonate Setting, Saudi Arabia

AAPG Middle East Region Geoscience Technology Workshop:
3rd Edition Carbonate Reservoirs of the Middle East

Datapages, Inc.Print this page

Insights on Characterization of a Shallow, Restricted Carbonate Setting, Saudi Arabia

Abstract

Identifying and characterizing the various lithofacies assemblages of mixed evaporate-carbonate succession within the Late Jurassic Arab Formation in the study area is an essential precursor to build the conceptual depositional model and it is the first step towards the aim of this study, which is generating the sequence stratigraphic framework of the targeted zone. This will aid in better understanding the lateral distribution of the depositional facies, hence building a robust geological 3D model. The cores have been described in detail to record the mineral composition, a modified Dunham texture, sedimentary structures, carbonate grain types, fossil assemblages, grain size, visual estimated porosity percentages, and porosity types. Different stratigraphic contacts have also been identified to define cycles and cycle sets. The studied section has eight major lithofacies deposited in a shallow restricted setting. Arranged from distal to proximal, 1) Intraclast floatstone/rudstone hosting anhydrite nodules along with distorted mud indicating possible dissolution or transgressive lag, 2) Peloidal mud/grain-dominated packstone deposited in a relative moderate energy environment either within the middle ramp or as intertidal beds where it hosted single anhydrite laths, 3) Peloidal skeletal grain-dominated packstone/grainstone with a diverse fossil content along with high angle cross bedding suggesting a moderate to high energy within a more open depositional environment although thin beds of this lithofacies can be found within the intertidal zone as transgression beds, 4) Thrombolitic wackestone/packstone indicating a restricted subtidal environment with a slight drop in salinity levels allowing the thrombolites to build up, 5) Pelletal packstone with reworked cerithic gastropods, coated grains, and microbial coated intraclasts along with occasional displacive anhydrite nodules and anhydrite laths indicating a shallow intertidal depositional environment, 6) Microbial/Stromatolitic wackestone to grainstone which was usually found to be cemented with anhydrite and host anhydrite nodules suggesting the deposition within the shallow subtidal zone close to the anhydrite, 7) Anhydrite, and 8) Fabric destructive hydrothermal dolomite. The third step is to generate cross sections with gamma ray, bulk density, and neutron porosity logs posted beside facies description, this will help better understand the facies behavior and further enhance the interpretation of the depositional cycles and facies lateral changes. Through this study, a total of six sequences have been identified. Three NW-SE cross sections indicate that the sediments were deposited under open marine conditions and tend to be thicker in a northern direction, whereas, the lithofacies deposited to the south indicate sedimentation under more restricted conditions, this is also supported by the overall variation in thickness of the evaporates. The hydrothermal dolomite seems to be a localized event concentrated on a small area to the North/West part of the field.