An Innovative Carbonate Facies Modeling Workflow That Honors Geological Concept, Case Study of Thamama

Abstract

Abstract Objectives/Scope One of the main uncertainties of reservoir modelling is understanding the reservoir properties in the inter-well region. Capturing variation in reservoir facies related to relative sea-level changes together with diagenetic overprint provides key information for the lateral reservoir heterogeneity. These observations can eventually be used as input for facies modelling to populate facies throughout the field. The conventional facies modelling approach defines lateral facies trends by using proportion data (pie-charts) for each reservoir zone. This approach has limitations to interpret lateral extension of individual facies or trends as the pie-charts show that all facies exist in the zone and everywhere throughout the field. However, incorporating the sequence stratigraphic concept into facies modelling workflow allowed us to draw discrete facies boundaries on sequence stratigraphic surfaces, which are of chronostratigraphic significance. Methods, Procedures, Process Integrated working sessions between sedimentologists and reservoir modellers lead to a new improved workflow in modelling reservoir facies. This case study provides a step-by-step workflow of the innovative facies modelling which is composed of three steps: Create vertical proportion curve (VPC) to capture vertical 1D heterogeneity associated with higher order of sea-level cycles Construct pie-charts at important and critical sequence-stratigraphic surfaces, such as Sequence Boundaries and Maximum Flooding Surfaces. At this stage, a conceptual geological model is established that will serve to identify facies trends and heterogeneity in 2D. Defining probability maps to control the proportion of facies laterally to ensure facies ratios respect to each other. Results, Observations, Conclusions This workflow was applied to multiple stacked reservoirs of one of the UAE Onshore fields. Results started to show how the depositional environment controlled facies distribution over the field and helped to control reservoir properties of individual facies. With this workflow, the lateral facies predictability has increased. Sedimentological maps now help better to understand possible pathways for hydrocarbon flow from injector to producer wells. Incorporating higher resolution sequence stratigraphic cycles helped to understand the high-perm zones that are dynamically important to capture. The method was further tested in other multiple ADNOC Onshore fields where new geological facies maps also revealed reliable geological trends.