BURRUS, JEAN, Institut Francais du Petrole, Rueil-Malmaison, France, JANVRY G. DE CHOPPIN, J. L. GROSJEAN, and J. L. OUDIN, TOTAL, Paris La Defense, France, T. SCHWARZER, Exxon Exploration Company, Houston, TX, and F. SCHROEDER and R. LANDER, Exxon Production Research, Houston, TX

ABSTRACT: Basin Evaluation in Deltaic Series Using 2-D Numerical Modeling: A Comparison of Mahakam Delta and South Louisiana/Gulf of Mexico Case Histories

Integrated numerical modeling of petroleum generation and migration is difficult to apply in deltaic series, because the extreme division of the facies makes it difficult to define bulk sedimentary facies and bulk properties at a scale appropriate for modeling. Using Institut Francais du Petrole's two-dimensional model TEMISPACK, we tried to simulate the petroleum history along a 70 km long east-west regional section in the Mahakam delta (Indonesia) and a 800 km long north-south section in south Louisiana/Gulf of Mexico. The two basins contain thick (>10 km) accumulations of the post middle Miocene. We argue that despite the particular difficulties mentioned, modeling enables explorationists to evaluate the fundamental processes that control petroleum generation and migration in de taic basins.

The principal results are as follows: (1) Both basins have similar overpressure profiles that are caused by thick shales with nano-darcy permeabilities. Compaction, not oil or gas generation, controls the overpressure histories. (2) In both basins, the thermal history is dominated by burial rate, thermal blanketing, and undercompaction. Basinward increases in thermal gradients are probably due to basinward increases in shale content and undercompaction, rather than geodynamic processes. (3) We used an upscaling procedure to define sedimentary facies and properties for each cell in the models. In both cases, we found a huge permeability anisotropy of interbedded facies was necessary to match observed pressure profiles and hydrocarbon distributions. This anisotropy results in a dominant "parallel-to-bedding" migration pattern, with only a moderate (< 0.5 km) vertical migration component. (4) A fundamental difference between the Mahakam and the Gulf Coast petroleum systems is the role of growth faults. In the Gulf Coast, huge growth faults connect deep overpressured, overmature Tertiary source facies with shallow, interbedded sandy reservoirs. Enhanced vertical permeability in the vicinity of these fault zones allows for several kilometers of vertical migration. In the Mahakam delta, where growth faults are less prevalent, deep overpressured shales have very poor expulsion efficiency; gas and oil in shallow reservoirs are shown to be fed mostly by coals located above, and not within, the overpressured zone.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.