Basin Modeling
The petroleum industry now ranks basin modeling as the top leadership technology that increases exploration success and lowers finding costs. Over the last decade, three-dimensional (3D) imaging and modeling of the subsurface through time have co-evolved and emerged as a major research focus of the petroleum industry. Virtually all major oil companies have independently recognized the need for 3D petroleum systems models because they:
1) Organize data, allowing deficiencies or inconsistencies to be identified,
2) Archive data (data loss due to personnel attrition and reorganization is a major cost factor),
3) Facilitate visualization of geologic processes and communication with stakeholders,
4) Add value by converting static data into dynamic processed data and interpretations, and
5) Require many disciplines to work toward a single goal.
Major application of 3D petroleum systems models can serve as evolving databases that provide surface and subsurface geologic information for various practical research needs. They allow users to figuratively look within the earth to examine data, appraise the reliability of geological concepts, models, or geochemical input, and extract needed information. Major applications of 3D geologic models include developing predictive exploration and reservoir models, integrating sequence stratigraphy and assessment units, predicting the extent and timing of petroleum generation in source rocks, structural deformation that disturbs basin architecture, migration pathways, and locations of potential traps and accumulations, and analysis of risk based on different geologic, geochemical, or fluid-flow assumptions. Thus, 3D petroleum system models can provide a basic geoscience framework to conduct and record a wide variety of applied and basic research.
As petroleum becomes more difficult to find and reserves become more difficult to replace, 3D petroleum systems modeling has grown because it better quantifies the generation, migration, and entrapment of the remaining resource. It also facilitates interpretation of the stratigraphic and sedimentologic processes that are important to develop a predictive sequence stratigraphic framework. Because of financial and time constraints, large oil companies typically conduct 3D modeling studies only at scales to suit their immediate needs. These studies commonly cover only the acreage held by each company and seldom cover the full extent of each petroleum system. This knowledge gap represents an opportunity for the USGS because many domestic and international companies are willing to supply data and expertise. Companies will benefit from USGS studies that extend 3D interpretations beyond immediate concession areas. For example, many oil companies exhaustively study “postage-stamp” areas within basins, but 3D modeling may not have been conducted over the entire area (e.g., Gulf of Mexico, San Joaquin, Permian, Los Angeles basins, North Caspian Basin).
3D petroleum systems modeling is rapidly growing as a tool to better understand subsurface migration, accumulation, and preservation. The approach is strong as a tool to predict the pod of active source rock, thermal maturity of the source rock, migration pathways, and the timing of petroleum generation. 3D modeling is currently less successful as a means to predict volumes of trapped petroleum, their detailed compositions, or the effects of secondary processes. However, solutions to these questions could have major impact on the domestic and world economy. 3D modeling is a tool that will continue to attract new users because of the potential for high-impact solutions to these problems with respect to exploration, development, and assessment.
Figure 1. Input geometry for a 3D North Slope, Alaska model. The study area polygon shows the position and surface shape of the 3D model (top). The 2D cross section along the key E-W wells (white vertical lines; bottom) was cut from the 3D input model. The 2D cross section was used to reconstruct the shape, current thickness, and eroded thickness of the prograding foresets in the Brookian section. The pre-erosional thickness (maximum burial depth) was determined using a linear extrapolation of measured vitrinite reflectance (Ro) on semilog scale for each well. Reconstructed lost overburden reaches up to ~4000 m in the western part of the section. This lost section controls the burial depth and thermal maturity of the source rock and geometry of the migration paths.
Figure 2. Simplified perspective view of a 3D North Slope model (note north arrow) is based on layered surfaces derived from well and seismic data. Rather than using a stratigraphic subdivision of the Brookian clinoform sequences, timelines of eastward prograding foresets were mapped to allow for a time-transgressive change of geometry. LCU = Lower Cretaceous unconformity.
Figure 3. Three-dimensional numerical models allow predictions of petroleum migration pathways and accumulations through time. Example shows predicted migration pathways and accumulations (green and red for liquid and vapor, respectively) on the North Slope above the Triassic Shublik Formation source rock (hatched gray) 14 million years ago based on a calibrated petroleum systems model created using PetroMod® software.
U.S. Department of the Interior |
U.S. Geological Survey
