An important objective of a surveillance programme for a gas condensate reservoir is to accurately assess reservoir pressure depletion over time. However, partial-to-complete isolation of zones throughout such a reservoir complicates the collection and interpretation of reservoir pressures from pressure transient analyses alone. As a result, production logs are run to obtain zonal flow contributions to understand the status of zonal pressure depletion. Understanding these zonal contributions and their implications on zonal pressures requires an integrated knowledge of the geologic and operational controls on flow.Integrated Geologic and Engineering Modeling Studies (iGEMS) is a workflow designed to provide this integration and, thereby, increase the value of surveillance data. iGEMS focuses on identifying well-level geologic and operation controls on flow. iGEMS uses an efficient process to rapidly create, run, and analyze single-well simulations that include the effects of boundary pressures and compositions inherent in the parent model.A case study utilising the iGEMS workflow is covered in this paper. This case study provides a specific example of how iGEMS teams identify geologic and operational controls on reservoir performance and develop a better understanding of zonal pressure differences. iGEMS provides insights on these controls by using reservoir modeling as a tool to integrate surveillance data, well logs, core data and geologic observations. Understanding what is controlling flow in the reservoir helps engineers, geoscientists, and petrophysicists make better operating decisions to maximise reservoir performance.

Monitoring individual layer performance (in commingled completions) and integrating the results into an overall understanding of field performance has always been a challenge. Overcoming this challenge allows for a better, layer-by-layer, understanding of the reservoir, and therefore will have a significant impact on well and reservoir management. This paper presents a success case for the integration of a novel approach, and specific applications are highlighted. The Khuff Formation of the North Field is a multi-layered carbonate reservoir formed from four main reservoirs; K1, K2, K3 and K4. As most of the RasGas wells are completed commingled through the main Khuff reservoirs, a hybrid approach for integrating multi-layer pressure transient analysis (PTA) with production logging tools (PLT) analysis of flow and pressure profiles was developed. The process also accounts for the physics of carbonate matrix acidisation. The outcome of this technique has helped RasGas better assess the stimulation effectiveness in commingled wells, and establish baseline performance for individual layers. This work was used to build improved inputs for reservoir simulation models, thus providing more accurate predictions of reservoir performance. Additional benefits of this technique have been: 1) identification of wells with impaired productivity (candidates wells for re-stimulation), 2) a better understanding of the stim jobs (areas for improvement for future jobs), and 3) an improved understanding of log kh vs test kh variation (to understand specific questions on well performance). This paper discusses the outcomes, applications, and the added value of this integrated methodology. The paper will also demonstrate examples where the technology was applied and the value that was added to the ongoing surveillance and future development activities.

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