A new method of simulation modeling was introduced to petroleum geology in late 1950s. Since then the method of the simulation modeling had given an incredible impact to the petroleum geologists. Geology is based on inductive method in which a scientific fact can be found from the pile of descriptive records, whereas geophysics is based on deductive method where a physical or mathematical model is developed assuming a uniformitarialism in the past before we extract a scientific fact through the model calibration. The model used in inductive method is called “Backward Model, ” whereas one used in deductive method is called “Forward Model.” The concept of forward modeling was introduced into geology through the application of simulation models. Geochemical models could give a big advantage to exploration geologists by which one can provide a reasonable map showing a history on oil/gas generation and migration. However, as we apply models for real exploration problems, we recognize a limit of model applications. It would be another advantage of forward modeling that we can experience many types of regional geology through using a model. This is called “educational effect” in which we can understand geological process rather than simulating a real world. If we define a first generation as people who have developed models by themselves, a second generation of basin modeler (users) can take in the “educational effect” most efficiently. If geologists, who have had a thinking based on inductive method, would acquire an additional deductive thinking by this “educational effect”, then it would produce new insight on the petroleum exploration and would result in a discovery of new oil/gas fields. The situation today is just before it when the number of second generation of basin modelers is getting increased.
A computer model “Facies-3D” has been developed to simulate the sediment distribution in deltaic and carbonate sedimentary environments. Three-dimentional sediment distribution is reconstructed on the basis of modeling of the sedimentary processes in these environments. In the simulation model, therefore, the emphasis is laid basically upon the understandings of the processes operating in the recent/ancient sedimentary environments and upon the numerical modeling of them. A case study of the Pleistocene carbonates from the Ryukyu Group distributed in Irabu Island in the southwestern tip of Japan is presented in this paper. The cyclic sedimentation of coral reef-dominant and rhodolith-dominant limestones found in the group is considered to reflect the relative sea-level change induced by glacio-eustasy, ranging over tens of meters during the Quaternary time. Taking these geological backgrounds into account, a series of simulation studies was conducted. The results successfully approximate the actual facies distribution if the tilting of the basement toward the west-southwest is assumed as the tectonic subsidence data. Significant control of tectonism, together with eustasy, on carbonate sedimentation was revealed and evaluated quantitatively through the simulation study. Another study has been conducted to simulate the sedimentary processes of the Miocene carbonate reservoir in the Walio Field in Indonesia. Preliminary results indicate that the model would be a useful tool for hydrocarbon exploration and exploitation, for understanding the geological settings and for reconstructing the sediment distribution in an area of interest, although several improvements are still necessary.
Seismic simulation technology has been developed for many years. Recent trend that targets of exploration have become deeper and more complicated recalls demand of the seismic simulation technology. However, it has been only used for limited study due to various technical reasons. In recent years, the seismic simulation technology is rapidly advanced with new simulation methods and parallel computers. We have developed the wave propagation methods and applied to various exploration problems. We will show some results of seismic simulation in this paper. The first example is related to the Marmousi model. This simulation result shows that the wave propagation is very complicated and is beyond our image. The second example is a virtual seismic survey related to the sub-salt play. The virtual exploration shows the problems and solutions for sub-salt seismic imaging. The third example is the difference between acoustic and elastic modeling. This result shows the problem in onshore seismic data and the future direction. Using a seismic simulation, we can recognize various pitfalls and limitation in seismic processing and seismic interpretation. Seismic simulation can be used as potential tools for virtual explorations. We can gain the knowledge and the virtual experience through the virtual explorations.
Naturally occurring complex processes of oil and gas generations in the source rocks can be simply approximated by several conceptual reactions; the primary cracking (oil and gas generation from kerogen), the secondary cracking (gas generation from oil), the formation of coke, and so on. The open-system pyrolysis and the selective hydrocarbon trap techniques are widely applied for the rapid method to calibrate kinetic parameters such as activation energy distribution, pre-exponential factor, and the composition of hydrocarbons from the primary cracking. Although kinetic parameters for the secondary cracking and the coke formation have not been fully tested yet, oil generation modelling is now practically useful for petroleum exploration. Modelling gas generation-expulsion in the deeper part of the basin is a major challenge to be overcome for the further development of basin modelling. For that context, we need more knowledge on reaction kinetics of thermal cracking of oils in the natural system. More plausible oil expulsion model is also required, since non-expelled oil can be one of the sources of thermogenic gas in the deeper part of the basin. The reconstruction of thermal history of the effective source rock is critically important for modelling the oil generation history. Reasonable thermal history can be reconstructed based on computerized geohistory diagram with multi-thermal indicators; fluid inclusion homogenization temperature, kinetics of fission track disappearance, authigenic mineral transformations, vitrinite reflectance, and biomarker thermal indicators. Kinetic models of vitrinite reflectance, which are applicable to non-linear thermal history, have been newly proposed and applied to the calibration of thermal history. If we have more accurate and quantitative models on heat flow history and organic matter distribution with basin evolution, the generation modelling can be more useful for petroleum exploration.
Numerical basin modeling simulators have been widely applied to petroleum exploration in recent years. Based on the observation and interpretation of the objective sedimentary basin, a geological conceptual model is constructed. The conceptual model is converted into input data for the simulator. When simulated results are consistent with the observation, the simulation is considered to be pertinent. The objective of the present study is to discuss the effects of heat-flow history and erosion on the vitrinite reflectance simulated by the one-dimensional maturity simulator “MATOIL®”. Recent and great changes in heat-flow history can be detected easily. Measured vitrinite reflectance scatters even at the same maturity level. Quantitative estimation of the heat-flow history is restricted by the reflectance scatter. Particular attention should be paid to the fact that different heat-flow histories by which almost the same present reflectance is simulated may provide different reflectance evolutions. An unconformity was observed between the Lower Oligocene and the Pleistocene to Pliocene (?) in the Well MITI Goto-nada. At the depth of the unconformity, vitrinite reflectance does not change significantly. Based on the reflectance simulation, the eroded sediment is estimated to be thinner than the present deposit on the unconformity. The present study shows that there may be plural conceptual models which give the simulated results consistent with the present observation, however, these conceptual models may show different maturation and petroleum generation histories. From the viewpoint of petroleum exploration, the numerical simulation should be attempted repeatedly using possible conceptual, models.
Modeling secondary migration and accumulation of hydrocarbons is one of the principal requirements in multi-dimensional basin simulation. In this paper, the treatment of secondary migration on basin simulators was discussed from both numerical and experimental point of view. Firstly, a new gridding method is proposed for increasing reproductivity by decreasing discretization errors, in which thin grids in both source/seal bed and carrier bed along their lithologic boundaries are constructed. Case studies using an imaginary siliciclastic sedimentary basin show that this treatment can reproduce secondary migration pattern that is close and consistent with those obtained from thinly divided grid systems without increasing cpu times and memory spaces. This treatment is also easily included into most of the previously developed basin simulators, thus, it would be an effective tool for modeling secondary migration in sedimentary basins. Secondly, displacement patterns are discussed based on the relative magnitudes among buoyancy, interfacial, and viscous forces using the results of one-dimensional vertical oil-water displacement experiments. Two displacement patterns are recognized during the experiments, one clearly formed a typical shock front and the other did not. Through trial-and-error matching approach using a two-phase fluid flow simulator, we found that the “shock-front” pattern can be reproduced by using typical relative permeability curves, while for “non-shock-front” case, we need quite different curves to reproduce observed results. It suggests that ordinary relative permeability curves obtained from special core analysis in the field of reservoir engineering might not be valid for modeling secondary migration. Such investigations would be important for improving our understanding of petroleum migration in sedimentary basins, and should be conducted in parallel with the application of simulators to actual basins.
Basin modeling studies have been utilized by most oil companies in order to understand the burial history, thermal history, generation and expulsion history of oil and gas in various basins. In particular, 1D and 2D basin modeling simulators developed by IFP-Beicip, LLNL, JNOC etc. have been applied. Such basin modeling simulators have been routinely performed for internal studies since the late 1980's by Idemitsu. New knowledge acquired between 1992 and 1997, from 1D and 2D basin modeling and experience in e.g. the methodology of the preparation of input parameters and the setting of a drainage area to evaluate the Northern North Sea suggest that the shale-out point of the Brent Group sandstone is one of the most important and sensitive geological parameters particularly in the assessment, of the degree of overpressure in the Upper Jurassic to Lower Cretaceous muddy strata, and in the type, mass and timing of expelled hydrocarbons. Significant comments on the methods of evaluation used in basin modeling, based on experiences from the simulation studies in the North West Shelf of Australia are also explained.
The petroleum system is defined by Magoon and Dow (1994) as a natural system which includes all geological and geochemical elements and processes essential to oil and gas accumulation. The concept itself is not new, but they reviewed and introduced a simple method to evaluate the petroleum systems. Basin modeling is one of computer simulation techniques which model generation, migration and accumulation of oil and gas in a sedimentary basin. In this paper, the emphasis is focused on that multi-dimensional basin modeling is one of the best techniques to evaluate the petroleum systems, since it can integrate many processes with quantitative evaluation on the history of sedimentary basins. Explorationists generally have several hypotheses or scenarios by the evaluation of present data. The artificial experiment by basin modeling can be compared with these hypotheses. Since each module forming whole basin modeling package is developed by the physical and chemical knowledge, basin modeling can give the constraint and reality on these hypotheses and hence reduce exploration risk. SIGMA-2D is a two-dimensional and three-phase fluid flow basin model developed by JNOC/TRC. The applications by SIGMA-2D to actual basins indicated that SIGMA-2D enables users to understand the petroleum systems very well. Once the users can understand the processes of the petroleum systems, unconventional plays and prospects will be easily identified. However, it should be kept in mind that quality, accuracy and reality of the simulations depend not only on the model itself, but also on the parameters for equations and input data.