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A Novel Approach for Predicting Sand Stringers: A Case Study of the Baka Field Offshore Nigeria

Authors
Obinna Chudi (Shell Nigeria) | Magnus Kanu (Shell Nigeria) | Austin Anaevune (Shell Nigeria) | Idris Yamusa (Shell Nigeria) | James Iwegbu (Shell Nigeria) | Oloniboko Sesan (Shell Nigeria) | Joel Musa (Shell Nigeria)
DOI
https://doi.org/10.2118/198766-MS
Document ID
SPE-198766-MS
Publisher
Society of Petroleum Engineers
Source
SPE Nigeria Annual International Conference and Exhibition, 5-7 August, Lagos, Nigeria
Publication Date
2019
Document Type
Conference Paper
Language
English
ISBN
978-1-61399-691-1
Copyright
2019. Society of Petroleum Engineers
Downloads
4 in the last 30 days
60 since 2007
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This paper details the seismic reservoir characterization study, aimed at predicting isolated sand lenses or stringers. Sand stringers or lenses are laterally discontinuous bodies that are encased in a different lithological body, they appear isolated and variable in lateral extent and thickness but mostly occur as thin beds. The thickness of these stringers makes it difficult for pre-drill predictions. One complicating factor of sand stringer is its potential of being isolated overpressured ramps which if unexpectedly encountered during drilling can cause kicks and if severe a blow-out is inevitable.

The Baka field is located some 120km off the coast of Nigeria in water depths of 2600ft (800m) to 3900ft (1200 m) with several wells drilled to date. Two of these wells have encountered unpredicted sand bodies that range in thickness from 15-25ft. These sand bodies were encountered within the Baka reservoir play interval of 5000 to 10000ft and were not predicted from conventional seismic reflectivity data, inverted seismic and offset well correlation. To obtain a better prediction of this stringers, alternative solutions are required. For this reason, a novel methodology - Geo-body constrained inversion approach was developed in 2017 to enable accurate prediction of stringer sands. Using this technique, a high-resolution acoustic impedance volume was built. Result of this study allowed the identification of gas bearing sand stringers encountered in previously drilled wells, thereby calibrating the model. The Geo-body inversion model proved a reliable tool for safe drilling of wells in 2018, ensuring that sand stingers were predicted at pre-drill phase in the Baka field.

File Size  1 MBNumber of Pages   11

AL-SIYABI, H.A. 2005. Exploration history of the Ara Intrasalt carbbonate stringers in the South Oman Salt Basin.Geoarabia, v. 10, no. 4, p. 39-72.

CHUDI, O. K. 2015. Predicting Oligocene Reservoir Potential in Deep-water Western Niger Delta: An Integrated Basin Modelling and Diagenetic Study. Unpublished PhD Thesis. Heriot-Watt University.

GROTZINGER, J. & AL-RAWAHI, Z. 2014. Depositional Facies and Platform architecture of microbialite-dominated carbonate reservoirs, Ediacaran-Cambrian Ara Group, Sultanate of Oman. AAPG Bullletin, v. 98, no. 8, p. 1453-1494

HUUSE, M. 2015. Sand Injectites in the North Sea and the Atlantic Margin: Giant Fields-Infill Targets- Drilling Hazard and Migration Paths. Force Conference Underexplored Plays, NPD, Stavanger.

HUUSE, M., CARTWRIGHT, J., HURST, A. & JACKSON, C., 2009. Large-scale Injectites in the North Sea: Seismic and Event Stratigraphy and Implications for Hydrocarbon Exploration. Search and Discovery Article, no. 4.

KESSLER, T. C., KLINT, K. E. S., NILSSON, B. & BJERG., P. L. 2012. Characterization of Sand Lenses Embedded in Tills. Quaternary Science Reviews.

STATOIL. 2013. Depositional Environment. Graduate Programe- Introduction to Sedimentology.

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