Estimating Reservoir Risk Using Stratigraphic and Thermal Maturation Modeling: An Application in the Galveston-High Island Region of the Gulf of Mexico

Laura Kay Ethetton, Scoot A. Bowman, Charley A. Rego, John M. Armentrout, Linda S. Rouch, Gary D. Harris

When exploring in a mature hydrocarbon province, where many remaining prospects are either subtle or difficult to detect, it is essential to have a technique to accurately assess geologic risk. Accurate prediction of the location of reservoir and seal rock, and structural timing is one way to reduce risk. Predicting this risk involves assessment of the presence and adequacy of porosity, permeability, thickness and areal extent.

Stratigraphic modeling is one technique to predict a range of values for these parameters that correlate with a viable reservoir and seal. It is used to build a section through the basin that matches present day sequence boundaries and maximum flooding surfaces interpreted from seismic data. The method consists of combining a depositional system with a sedimentation, subsidence, and eustatic history that reconstructs the geologic history along a series of 2D cross-sections. These reconstructions not only predict the depositional environment but form the basis for defining the geometry and timing of structures and their relationship to reservoir and seal formation. The predicted primary porosity and permeability, coupled with thermal maturation of organic material and fluid flow, were sed to constrain the model with the known hydrocarbon accumulations.

One thousand trials were executed over a range of reasonable values for depositional variables (such as percent sand content) producing a probability distribution for the presence of sand. The result is a probability map of the occurrence of sand anywhere on the cross-section. Similar maps of the other parameters are then produced which are multiplied together to constrain the probability of hydrocarbon occurrence and define the probability of a geologic success.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995