Facies architecture is widely accepted as an efficient method to characterize subsurface reservoir within specific architectural elements hierarchically in the last two decades. The distribution and type of architectural elements, (e.g. distributary channel complex, distributary bar complex and mouth bar complex) within the delta system have a major impact upon reservoir compartmentalization and the distribution, continuity and connectivity of sand bodies.
The paper take South Jinzhou 25-1 Oil Field, offshore Bohai Bay Basin, as an example, characterizes the architecture of the braided reservoir in utilizing 94 wells’ data and 3D seismic data covering an area of roughly 430 km2. The second member of the Shahejie Formation is typically deposited in braided delta, characterized by sandstone-conglomerate deposition with medium porosity, medium permeability and high heterogeneity. Prediction of the three dimension of reservoir architecture and petrophysical property is critical to provide recovery strategy for reservoir and facilities plan which contribute to the high efficient development of the field.
In this study, core and wire-line log were used under the guidance of Miall's theory, and 10 types of litholofacies are identified: M, Fr, Fh, Fm, Sw, Sh, St, Sp, Sm, Gm. In utilization of wire-log and seismic interpretation, based on the sand body scale, the hierarchy of braided delta sand body was divided into 6 levels: bed, bed set, channel bar/channel accretion, channel bar/channel, channel bar/channel compound and braided delta from small to large. Based on the sediment process，the superimposed sand body pattern was divided into two main types: distributary channel-mouth bar pattern and distributary channel-distributary bar pattern which indicate a lower energy deposition and a higher energy deposition separately. With the help of well section analysis and strata slices, four main patterns between architectural elements was summarized: associated coeval channels, associated channel-bar, unassociated channels and unassociated non-coeval channels. The magnitudes, widths, and thickness of single channel and bar was predicted by a comprehensive approach. The magnitudes, widths, and thickness of single channel and bar was predicted by a comprehensive approach. The advantage single channel-scale architecture elements, single channel, were about 200m wide and 6m thick. In channel accretion-level, channel edge was in poor properties with fine grains, while channel center had better properties with coarser grains which indicate high quality reservoirs.
Topics: Deltaic depositional systems , Topics: Shelf and shallow water sedimentation , Topics: Lacustrine sedimentation
