State of the Art of Basin Modeling

D. H. Welte

The purpose of computer-aided integrated basin modeling is to understand and reconstruct the geologic evolution of a sedimentary basin, to quantify this information numerically, and to derive from this, in quantitative terms, the generation, migration, and accumulation of hydrocarbons. For integrated basin modeling, three main steps can be distinguished: (1) geologic basin modeling, (2) geochemical modeling, and (3) integration of results from the first two steps to define an exploration strategy.

The conceptual model describes the sequence and type of geologic processes occurring during basin evolution. The basin evolution is subdivided rigorously into a continuous sequential order of geologic events (processes) with exact times of duration in millions of years correlative with the geologic time axis. The backbone of a conceptual model is a stack of isopach maps characterizing all layers and events with their physical, thermal, and geochemical properties.

Information from so-called "key wells," which should represent the geologic evolution of a certain part of the basin, is used to test and calibrate the conceptual model against actual data. During these one-dimensional simulation test runs of key wells, important parameters such as sediment thicknesses (total and individual units), porosity, temperature, pressure, maturity, and hydrocarbon generation potential are compared and matched by special iteration techniques. After successful optimization and calibration of the key wells, the hydrocarbon generation for recognized source rocks is simulated using a kinetic (rather than a maturity) approach. Kinetic equations can be used because the computer simulation provides a detailed temperature history for any given point in the basin.

The expulsion of hydrocarbons from source rocks is important when determining the charge available to fill existing traps. Therefore, expulsion efficiency models of various degrees of sophistication are valuable. They include the minimum degree of hydrocarbon saturation and hydrocarbon generation rates. In this way, a more accurate determination of amount and timing of hydrocarbon charges is possible. The prediction of hydrocarbon accumulations can be complemented by conventional secondary migration considerations on the basis of the model results. If a sufficiently detailed data base is available, a secondary migration model based on a buoyancy and capillary pressure concept is applied.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.