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ABSTRACT: Three-Dimensional Computer Simulation System of Deltaic Sedimentary Sequences

Takao Iwata, Yamamura Tsuneo, Sunouchi Hisao, Miyata Yuichiro

A computer simulation system to help predict the distribution of deltaic sandstone reservoirs is being developed. The main components of the system are jet-flow, density-flow, and bed-load transportation models. The prototypes of the jet- and density-flow models have been completed.

For the jet-flow model we apply the theory of Wang, who described turbulent plain jets that discharge into quiescent bays. Primary input

parameters are location and dimensions of the river mouth, flow velocity, sediment concentration, and physical characteristics of sediment and fluid. Distribution and thickness of deposits are the output results of our simulations.

The density-flow model is a three-dimensional process-simulation model that simulates unsteady turbidity underflows that occur at river outlets in freshwater lakes and on relatively steep submarine slopes. The model is designed to describe sedimentary processes which occur in a geologically short time. It takes account of effects of bottom-surface slope on sedimentation and self-acceleration according to density changes caused by entrainment of basement materials. Input parameters are locations of sediment sources, physical characteristics of fluid and sediments, and initial basement elevation. Sediment thickness and distribution are obtained as output.

The program is written in Fortran 77 for Apollo engineering workstations. Operation of the system is menu driven except for entry of input parameters. The graphics program utilizes the Apollo 3D-GMR graphics library, and graphics output include three-dimensional and cross-sectional displays of simulated sediments.

In actual sedimentation processes in deltas, various forces affect morphologies of deltas and distribution of sandstones. We are now adding models of wave action, longshore currents, and water-level changes to the system.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990