Seismic Stratigraphy and Geomorphology of Bibiyana Gas Field, Bangladesh: How the Recognition of Unconformities Led To a Better Understanding of Reservoir Architecture and Distribution
Kenneth D. Ehman1, Bill Kowalik2, Ken Cass3, Yan Chen2, Jeff Roche2, Henry Posamentier1, Doug Meyer4, David Reeves3, Andrew Royle1, Andrew Warnock2, and Paul V. Anderson5
1Chevron Energy Technology Company – Houston, TX, USA
2Chevron Energy Technology Company – Perth, Western Australia
3Saudi Arabian Chevron – Kuwait
4Chevron Thailand Exploration and Production, Bangkok, Thailand
55Chevron Bangladesh – Dhaka, Bangladesh
A sequence stratigraphic model was constructed for the Chevron-operated Bibiyana gas field in Bangladesh that integrates 3D seismic reflection volumes with the existing wells in the field. Bibiyana Field is currently producing approximately 800 MMSCFD and accounts for over 35% of Bangladesh's daily gas supply. The stratigraphic model was used to define and delineate geobodies that were incorporated into both static and dynamic reservoir models. Using seismic stratigraphic/geomorphologic workflows, the architecture and distribution of the reservoirs at Bibiyana field are now better understood.
The field is divided into five sequence stratigraphic units, each recognized by seismically defined sequence boundary at both the base and at the top of the units. The key reservoir sands are divided into two general categories: 1) erosional remnants below sequence boundaries (i.e. BB60, BB76, BH10, and BH20); and 2) incised canyons above sequence boundaries (i.e. BB58, BB70, BB72, BB74, and BH16). For example, the BB60, the main reservoir containing approximately 50% of the modelled reserves, is an erosional remnant below a major sequence boundary (SB60) sealed by the thick canyon fill shale of the BB55 interval. Locally, at the base of the canyon, "deepwater" turbidite-dominated sandstones are present (BB58) and have reservoir properties that contrast with the underlying and adjacent shallow-water, tidal-dominated sandstones of the BB60 reservoir. Reservoir pressures are directly related to the position relative to the sequence boundaries. The pressure barriers are the transgressive shale units that fill the canyons above sequence boundaries. Review of the pressure data from the wells helped refine the final sequence stratigraphic correlation.
A well top data base was used to integrate the petrophysics with the geobodies in the reservoir model. Geobodies were defined by tying the seismic reflection data to the existing well log data. Eighteen geobodies were defined representing the major reservoir intervals in the field. The geobodies were defined in VoxelGeo, exported and refined in Petrel, then finally exported to Gocad for the model building.
The recognition that unconformities with overlying canyon-fill shales seal many of the reservoirs at Bibiyana is critical in understanding and modelling the reservoir architecture and performance over time. The sequence stratigraphic model of the Bibiyana field provides the cornerstone to both the static and dynamic reservoir models, currently being developed for the field. In addition, the new stratigraphic model is being used to optimize ongoing development drilling. The sequence stratigraphic framework provides a framework to identify additional leads and development opportunities in the field.
The Bibiyana project is an excellent example of how multiple Chevron teams worked together to deliver high-quality, state-of-the-art products that accommodated both our business partner's needs, and enhances the understanding of reservoir architecture and distribution within the largest gas field in Bangladesh.
AAPG Search and Discovery Article #90206 © AAPG Hedberg Conference, Interpretation Visualization in the Petroleum Industry, Houston, Texas, June 1-4, 2014