Analysis of amplitude changes versus offset in seismic data is proving to be a valuable tool in locating gas reservoirs. However, in order to establish the importance of the anomalies it is necessary to calibrate to known data or make an educated estimate of rock properties in the seismic profile. Stratigraphic simulation provides a technology for predicting the size and positions of reservoirs and their associated rock properties and the presence of hydrocarbons from a limited dataset.
Basim is the most complete stratigraphic simulation and hydrocarbon generation and migration system available. This system provides a tool for dynamically modelling the distribution of lithofacies as well as hydrocarbon generation and migration history. The program allows you to simulate siliciclastic and carbonate deposition in many tectonic settings. The model builds a depth section with a description of possible rock properties that include lithology, porosity, fluid type, pressure, and temperature.
The input data includes two-way travel time horizon data from workstation interpretations, horizon ages and depths from well logs and checkshot surveys, and estimated paleobathymetric profiles for each horizon. This information is statistically compared with the model results and automatically "inverted" by adjusting the depositional and tectonic process inputs to determine a best-fit model for the given observations.
The stratigraphic simulation can be iteratively run, fine-tuning the tectonic process and sediment supply parameters within the window of possibilities determined by the observations. The results are sampled for various conditions, such as the presence of a particular sand type or porosity greater than a predetermined value. The result produces a probability of encountering that condition.
The model calculates the rate of siliciclastic sediment influx over time. This information can be used to estimate channel width and depth, as well as document important shifts in deposition in and out of the play fairway.
A distribution of Vp and Vs can be calculated from the stratigraphic model using the White-Boltzman equation or similar method and values of the bulk modulus of the matrix and framework material (which vary as a function of lithology, age, depth, and porosity), and pore filling fluid. Porosity is modeled as a function of depth or overburden stress. Density is calculated as a function of the mineral type and porosity. An impedance/reflectivity model can be determined from the distribution of velocities. The fluid content, as calculated by the fluid-flow model, can also determine the velocity of the rock.
In addition to calibrating the velocity state of a seismic profile the simulator may also suggest new play types or positions of important unconformities and associated hydrocarbon bearing reservoirs.
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