222-3 Integrated Lithofacies, Grain Size, and Diagenetic Controls on Reservoir Quality in a Tidally Influenced Coastal Plain System: A Case Study from Tumu5 interval (11790.00-11821.50 ft) in the X-4 well, Niger Delta, Nigeria.

Session: Delta Evolution from Rivers to the Shelf: Past, Present and Future Perspectives for Society (Posters)

Presenting Author:

Authors:

Abstract:

A proper understanding of the interplay between sedimentary facies, grain size distribution, and diagenesis is critical for accurate reservoir characterization in complex marginal marine systems. This study presents an integrated sedimentological and detailed core analysis from the Tumu5 interval (11790.00 - 11821.50 ft) in the X-4 well, Niger Delta, Nigeria, located within a tidally influenced coastal plain setting. A detailed description of the cores identified three principal lithofacies: Planar/Parallel Laminated Sandstone, Bioturbated Sandstone, and Massive-Laminated Mudstone. These were further characterized into two distinct genetic reservoir units, the Mouthbar Sandstone and Coastal Plain Shale, based on depositional processes and stacking patterns.

Grain size analysis using both sieve and laser particle size analysis methods revealed significant methodological differences, particularly in the quantification of fine versus coarse fractions. Conventional sieve analysis accurately indicated the sand-dominated nature of Planar/Parallel Laminated Sandstone facies, confirming their reservoir potential, while laser particle size analysis was more effective in resolving the fine-grained properties of the non-reservoir Massive-Laminated Mudstone facies. The Bioturbated Sandstone facies exhibited mixed signatures, reflecting bioturbation-related mud infiltration, and this significantly impacts permeability.

Further depositional interpretation, supported by studied sedimentary structures, ichnology (including the Palaeochycus, Ophiomorpha and Planolites), and electrofacies trends, indicates alternating tidal and fluvial dominance within a dynamic coastal plain. Diagenetic features such as localized carbonate cementation, pressure solution, and kaolinite and chlorite authigenesis, further influenced reservoir heterogeneity, primarily through reduction in porosity.

This multi-disciplinary approach underscores the importance of integrating core sedimentology, integrated grain size techniques, and diagenetic data to interprete reservoir heterogeneity in tide-dominated system. The findings from this study have direct implications for facies-based petrophysical modeling and reservoir quality prediction in analogous depositional settings.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5393

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.