BASIN/PETROLEUM SYSTEM MODELING
Basin Modeling refers to a group of geological disciplines used to analyze the formation and evolution of sedimentary basins in order to help evaluating presence and type of hydrocarbons, and resource potential.
By doing so, valuable inferences can be made about presence and maturity of potential source rocks, hydrocarbon generation and timing of expulsion, and migration pathways of expelled hydrocarbons and the petroleum system(s) in a basin will be understood.
The burial history of the basin (seismic data, wells)
The thermal history of the basin (wells)
Source Rock (%TOC, kerogen type; maturity history)
The expulsion, migration and trapping (structure, seal) of hydrocarbons
Review of geochemical studies done on wells in the basin (RockEval)
Reservoir quality (diagenesis; petrography)
Type and volume of hydrocarbon-in-place
Integrated basin and petroleum system modeling (BPSM)
The petroleum system concept becomes important when deep burial of source rock yields thermogenic oil and/or gas. A petroleum system consists of four essential elements (source, reservoir, seal, and overburden rock) and two processes (trap formation and generation-migration-accumulation). Petroleum systems occur in sedimentary basins, but not all sedimentary basins contain petroleum systems. To quantify petroleum systems, one must first model basin geohistory.
Process workflow diagram for Basin Petroleum System Modeling (from: Peters et al., 2008; USGS Professional Paper 1713, Chapter 12, p. 1-35).
Basin modeling enables geoscientists to investigate the dynamics of sedimentary basins and their associated fluids to determine if the past conditions were appropriate to fill potential reservoirs with hydrocarbon and preserve the potential reservoirs. Basin modeling applies mathematical algorithms to seismic, stratigraphic, paleontological, petrophysical, well log and geologic data to reconstruct the deposition and erosion of rock layers through space and time; in other words the evolution of sedimentary basins.
OPS OES Thailand can deliver expert modelers, who are able to execute all necessary steps to complete a full-blown, detailed basin model. In addition, our geologists are also capable of utilizing industry standard 1D basin modeling software to un-raffle the dynamics of sedimentary basins and associated fluids. Today, there are numerous software packages available, from simple to sophisticated.
Burial History (seismic data and wells)
The simplest, 1D or single-point model, examines burial history at a point location, usually a well (Figure 1), sometimes a pseudo-well location. Two-dimensional modeling, either in map or cross section, can be used to reconstruct oil and gas generation, migration and accumulation along a cross section. Three-dimensional modeling reconstructs petroleum systems at reservoir and basin scales and has the ability to display the output in 1D, 2D or 3D, and through time; if the time dimension is included, the modeling can be considered 4D.
Close interaction of the modeler and the geologist and geophysicist is of utmost importance. The modeler relies on the input data, such as missing section in a well, uplift and erosion or non-sedimentation when building his burial graph model.
Figure 1: Example of a burial graph.
Thermal History (wells)
In addition to the burial history, the thermal history of the basin is modeled. OPS OES geologist or modelers calibrate uncertain thermal input data, such as palaeo heat flow values in their model, with measured data in geochem reports from well, when available. Calibration parameters are vitrinite reflectance (Figure 2), biomarkers, RockEval data, such as Tmax values, isotope fractionations, fission track analysis, biodegradation, source rock analysis (e.g. TOC%) etc. Temperature data from well logs can be used to calibrate uncertain thermal input data, such as paleo heat flow values.
Figure 2: Maturity calibration model: Depth vs. Vitrinite Reflectance (%Ro).
The calibrated maturity model in Figure 2 tells us at what depth a potential source rock enters the oil- and gas window. It shows a good match between the modeled thermal maturity and the VR data points from the well. It will also help the modeler/geologist to predict what reservoir fluid may be present.
Basin modeling will enable us to understand the so-called petroleum system by predicting the timing of petroleum generation, expulsion and migration relative to the trap formation, very important in geological risking. Timing of petroleum generation is also important in relation to the formation of faults, which act as migration pathways. Lastly, modern software packages help to predict the type and amount of expelled hydrocarbons. The output diagrams in basin modeling reports using modern software are very illustrative.
BPSM technology has become an indispensible tool for exploration and is now employed by the major service providers to the industry, as virtually all oil companies recognize the need for basin and petroleum system models. Software development continues to accelerate. In the future, it is likely that more compositional kinetic models will be calibrated using measured reservoir pressures and compositions of reservoir fluids. It is expected that BPSM will play an increasingly vital role in exploration, similar to the now indispensable role of reservoir modeling in production.