Anthony J. Park1, Kagan Tuncay1, Matthew Laroche2, John Comer3, Peter J. Ortoleva1
(1) Lab. for Computational Geodynamics, Indiana University, Bloomington, IN
(2) Chevron USA Production Company, Houston, TX
(3) Indiana Geological Survey, Bloomington, IN
ABSTRACT: Comparing Observed Overpressuring and Fracturing Characteristics of Siliciclastic and Carbonate Sediments and Basin.RTM 3-D Simulation Predictions
Fracturing is a result of the interaction between tectonic stresses and pore fluid pressure. Stresses are transmitted through sediment depending on its properties. In contrast, fluid pressure reflects sediment deformation and compaction histories, as well as associated porosity/permeability changes and the presence of hydrocarbons. Thus, characterizing the distribution and the conditions for fracturing requires an understanding not only of the tectonic history, but also how the sediment evolved in geologic time.
Basin.RTM is a comprehensive 3-dimensional basin simulator that implements visco-elasto-plastic rheology, dynamic fracture mechanics, and a composite-medium approach to describing sediment properties. By using well-log and other geologic information as the input data, the simulator has been able to match fracture generation, distribution, and overpressuring and seal-formation histories of various basins. These results are used to assess discrepancies between the pre-drilling expectations and the observed reservoir quality.
Simulations show that fractures occurring in interbedded fine- and coarser-grained sediments (both siliciclastic and carbonate) are strongly dependent on the thicknesses, compaction histories and sealing properties of these layers. Generation and presence of oil and gas is intrinsically associated with the overpressuring-fracturing-healing cycles occurring in the sediments. Also, while the presence of 1 to 2% by volume of Types I and II organic matter in fine-grained sediments may not affect their mechanical properties significantly, amounts greater than 5% by volume may have appreciable affects on their fracturing characteristics.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado