3-D Turbidite Forward Modelling for Exploration and Geohazard Studies

Abstract

In many explored basins, turbidite sandstones are hydrocarbon reservoirs with excellent properties but also with a high degree of heterogeneity, associated to their internal facies distribution, which is often difficult to define from seismic data away from well constraints or in undrilled areas. In addition, modern gravity-driven flows may represent an issue in engineering projects focused on the design of subsea facilities.

Forward modelling provides information concerning the prediction and quantification of the vertical/lateral distribution of sedimentary facies within stacked turbidite bodies, the main hydrodynamic parameters associated to the flows and their transformation down current.

For these purposes, a proprietary 3D forward modelling tool was developed for modelling the complex hydrodynamic behavior of gravity flows, as well as the geometry and internal characteristics of their associated deposits.

Two cases are presented to give an example of software simulations and main results, in both ancient and modern turbidite settings.

In the exploration example, the initial sea floor topography and the overall geometry of the analyzed turbidite system were reconstructed from seismic. Basic information concerning the grain size distribution and the average bed thickness were derived from neighboring wells. The overall lateral-vertical facies distribution was built through the simulation of subsequent depositional events. Both dense and turbulent currents were modeled varying sediment grain size and concentration into the initial flow to test changes in the related depositional bodies and their internal sediment distribution. Simulation results provided quantitative information concerning the distribution and thickness of the expected reservoir deposits.

In the modern example, besides sedimentation and erosion processes, further hydrodynamic parameters were quantified such as flow velocity and its variation through time, event duration and pressure wave effect near the route of a planned pipeline. The simulations were run on a high-resolution sea floor bathymetric map to test different flows and quantify the potential effects of their impact on the subsea facilities. When these simulations are performed during the early phase of a geohazard campaign, they can significantly contribute to the risks assessment and to the development project optimization.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018