Assessment of the Influence of Fault-Associated Fracture Corridors Through Integrated Geological-Engineering Sector Screening: A Game Changer for Optimizing Reservoir Management Practices in a Giant Carbonate Onshore, Abu Dhabi U.A.E.
Authors: Farnetano Ruben Pinto , Gutierrez Rodrigo , Freites Alfredo , Torres Kevin , Alnuaimi Eiman 
Published: January 2023

The sector screening review is a surveillance tool used to assess and find opportunities to increase the oil production and improve the performance of the reservoir. We developed a novel interdisciplinary workflow (geology-engineering) integrating dynamic and static data in order to generate opportunities at well and field level; this methodology was used to analyze the impact of fractures in the reservoir performance and management.

The complexity of the geology on areas near a graben system (structure at center of the field with biggest vertical displacement) was suspected to cause flow anomalies that ultimately affected the well productivity indexes. After an exhaustive evaluation, it was noticed that a well showed lower productivity index (PI), 2-3 times less than nearby producers in the area, same reservoir Unit Z2 (similar lengths, conditions). To understand the root cause of such performance, a geoengineering workflow was implemented, integrating pressure transient analyses (PTA), production logging (PLT), bottom hole image (BHI), seismic (exceptionally complete dataset) and extrapolated to other wells with similar behavior.

The PLT showed that 70% of the well contribution was concentrated in only a small interval of the horizontal section, this interval was correlated to a conductive fault through BHI, which was also detected by seismic (correlates with low velocity anomaly). The PTA showed unexpected pressure transient behavior suspected to be related to the dynamic effect of the fault and associated fractures.

Learnings from above analyses triggered actions in different scales/stages: at Well scale, 1st Stage: the well was selected to be completed using selective stimulation with abrasive jet, to remove damage of the first 400 ft. of the well (skin factor masked by fracture contribution) and unlock the potential of non-contributing zone (after fault, to toe); allowing the well to produce 25% additional oil and doubling the PI. 2nd Stage (planned): workover proposal to install lower completion (LC), to ensure even depletion, avoid by-passed oil and prevent early water/gas breakthrough. Field scale: new wells to be drilled in reservoir zones potentially affected by the graben will be equipped with LC. Finally, a geological well testing framework matching the PBU and PLT was implemented based on a high resolution geological model designed to capture the properties of the matrix and fractures. The results from this study were used as diagnostic tool for additional wells with similar conditions which lack PLT data.

Noticeably, the presence of flow controlling fractures was usually suspected but not properly assessed/quantified in this reservoir, mainly due to the fact that the dynamic impact of these fractures was masked by the overlapping of different geological phenomena. The implementation of our geological-engineering workflow allowed immediately triggering actions that could lead to major performance enhancements at field- and well-level, including field development, management and modelling practices in such complex geological arquitectures.