Proactive Surveillance Enhances Reservoir Characterization in Mature ACG Field

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 230423, “Proactive Surveillance Enhancing Reservoir Characterization in a Mature ACG Field,” by Rizvan Ramazanov, SPE, Mardan Tahmazli, and Fidan Selim-Zade, BP, et al. The paper has not been peer-reviewed. _ Effective management of mature fields relies on a deep understanding of their complex dynamics. This challenge is intensified by the heterogeneous nature of reservoirs under production and water and gas injection. Successful reservoir management comes from proactive and continuous integrated analysis of surveillance data and multidisciplinary collaboration. The complete paper showcases examples of how integrated analysis of surveillance data in the Azeri-Chirag-Gunashli (ACG) field has improved reservoir understanding and informed reservoir-management decisions. ACG Field Surveillance Proactive surveillance plays a critical role in effective reservoir management in mature oil and gas fields. Achieving understanding of both static and dynamic reservoir characteristics and ensuring well integrity depends on timely surveillance programs and the integrated interpretation of data by a highly qualified multidisciplinary team of specialists. This approach provides the foundation for optimizing reservoir performance and enabling timely interventions, well work, and infill-well drilling. Eventually, such practices not only protect production from the existing well stock but also create opportunities for enhancing recovery and sustaining long-term field performance. The ACG field off the coast of Azerbaijan is one of the most mature offshore oil assets in the Caspian Sea, with sustained production for more than 25 years. Its reservoirs belong to the Pliocene-aged Productive Series and are composed of alternating sand and mudstone sequences. Within this stratigraphic interval, the Fasila formation is dominated by laterally extensive, well-connected sand bodies, while the Balakhany formation presents a more geologically complex setting with significant heterogeneity. Field development began by targeting the Fasila sands; however, over time, production from the Balakhany interval also was introduced. At present, both formations contribute to field production, with some wells developing from individual horizons and others designed for commingled production. The majority of the ACG well stock was drilled with high deviation and completed with openhole gravel packs (OHGP) to provide effective downhole sand control. ACG reservoir pressure is maintained through peripheral water injection, supplemented by crestal gas injection in the Azeri sector. Heterogeneity, structural features such as faults and fractures, and well-integrity concerns can cause injected fluids to migrate into unintended zones, posing risks to future infill targets. To address these uncertainties, a high-definition ocean-bottom-node 4D seismic program has been launched, with surveys scheduled annually over a 5-year period. The seismic results provide critical insights into contact movement and the ACG reservoir’s complex architecture but require integration with production and injection history, formation petrophysical parameters, and other surveillance data. Integration of these diverse inputs, coupled with detailed risk assessment and readiness for unexpected formation fluids, is fundamental for the successful delivery of new wells.