ABSTRACT: Basin Analysis in a Tertiary Delta by Numerical Modeling: Mahakam Case Study (Indonesia)

Jean Burrus, E. Brosse, Y. Grosjean, G. Choppin De Janvry, J. L. Oudin, G. Bessereau

The evolution of the Mahakam delta is discussed on the basis of a quantitative reconstruction using the two-dimensional TEMISPACK software developed at Institut Francais du Petrole. The following steps are achieved.

(1) An east-west 80-km-long regional seismic line tied on wells is used to establish a depth-section, divided in 25 chronostratigraphic levels, and 40 vertical columns. Fifteen different lithologies are distinguished (between shales and sandstones, with variable total organic carbon), as interpreted from well data and seismic profiles.

(2) Porosity-depth relations derived from log-data are used to backstrip the section and reconstruct the past geometries. The development of geopressures is investigated after calibration of the permeabilities on the observed lithologies. In particular, we account for the small-scale variations of the sand/shale ratio by introducing a high anisotropy of the permeabilities. The model is shown to reproduce well observations such as depth at which geopressures appear, and gradients of pressure in the overpressured zone. The simulations show that the geopressures essentially are controlled by the distribution of the sandy layers, and are due to compaction disequilibrium.

(3) The generation of hydrocarbons simulated by a kinetic model and the migration (separate phase flow) of hydrocarbons is discussed. Boundary conditions and underconstrained parameters, such as capillary forces, past heat flow, etc., are discussed on the basis of a sensitivity analysis.

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