Architecture of Deep Water Lacustrine Fans Fed by Multidirectional Clinoforms in Dacian Basin, Romania
The models for lowstand and highstand basin floor fans are well known from multiple studies. In this study an additional complexity is added to basin floor fan architecture where sediment is fed to basin floor from multiple directions. Late Miocene clinoforms (300-450 m height) are easily recognized in 3-D seismic of western Dacian Basin, a para-Tethys basin in Romania. The clinoforms are more difficult to recognize in well logs but in seismic data a 100-150 m thick lower interval with coarse sandy deposits overlain by 150-200 m thick muddy deposits and capped by 50-100 m thick sandy deposits, is well imaged. Depositional systems on shelf, shelf edge, slope and basin floor were mapped on seismic data and also recognized on well logs. The Dacian Basin was a closed basin with clinoforms prograding from multiple directions toward its center. 3-D seismic combined with five strike-oriented and two depositional dip-oriented well cross-sections are the main tools to investigate basin floor fans architectures. SP and resistivity logs of some 400 closely (~300 m) spaced wells have been correlated over an area of thick basin floor fans. The overall fan thickness is >200 m and the fans can be followed on the seismic data for hundreds of kilometers. The fans are composed of 10-30 m thick sandstone units interpreted as fan lobes. The lobes have complex sandstone distributions with coarsening or thinning upwards, blocky or ratty log patterns suggesting variable facies. Individual lobes extend from the lower slope and onto the basin floor. In the ‘distal’ area of one clinoforms the fans have thicker sandstone as these represent lobes formed by sediment shed from a different segment of the basin margin. Multiple directional deep-water fans coalesce to create thicker than normal sandstone bodies but with complex internal architecture. We are able to document sandstone lobes with different orientation and variable thicknesses through time, as these are linked with variable rates and directions of basin margin progradation. As a consequence, new plays and prospects with unusual fan configurations are described. There are no recognized hydrocarbon deposits in the described fans but elsewhere in the basin, equivalent age deposits form reservoirs.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017