Palaeo-Bathymtic Surfaces and 3-D Modelling of Sand Deposition

Abstract

Deposition of sand and shale units from turbidity currents may form self-contained hydrocarbon systems. As such, units within these systems may consist of high quality sand reservoirs between layers of shale, which can act as both a source rock and a seal. Parameters such as grain size distribution/sorting; the volumetric concentration of sediment within the flow and; the initial flow dimensions control the character of each flow and its ability to transport sediment. Changes to these parameters influence the distance a sediment load can be transported and its rate of deposition. Using numerical models to simulate turbidite deposition in deep water settings can provide a quick and inexpensive means of predicting the position and quality of potential reservoir sands. The path a turbidity current follows and subsequent pattern of deposition is strongly influenced by the topography of the sea floor. Flows may be blocked, deflected or accelerated depending on the size of a ridge or scarp and the relative angle of incidence to the obstacle. Within Move™, Palaeo-bathymtic surfaces can be generated using 3D Kinematic Modelling module to restore deformation, sediment compaction and isostasy. Industry standard workflows typically involve the sequential backstripping of 2D interpretations to the desired Palaeosurface, to define the restoration sequence. The same workflow is then applied to 3D surfaces in order to obtain a restored palaeo-bathymetric surface. The geometry of the restored surfaces can be used to assess the deformation style at the scale of the study area and the sequence of deformation events which led to the development of the present-day structural geometry. Turbidity flows are then run across this surface to investigate sedimentation, for example to: test basin entry points; predict amount of sand; determine the net:gross relationship and distribution, or simulate multiple scenarios and compare the predicted sediment attributes to observed data from wells to identify the best-fitting flow or flows (inverse modelling). Predictive maps showing detailed grain size distribution analysis and reservoir quality of simulated turbidite deposits may be used as a reconnaissance tool to identify new targets or to analyse and explain depositional patterns of turbidity currents. In turn these numerical models can help to refine the restoration workflow and understand the implications of seabed structures.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015