Geological modelling

To a large extent the reservoir geology controls the producibility of a formation, i.e. to what degree transmissibility to fluid flow and pressure communication exists. Knowledge of the reservoir geological processes has to be based on extrapolation of the very limited data available to the geologist, yet the geological model s the base on which the field development plan will be built. 

To derive a reservoir geological model various methods and techniques are employed mainly the analysis of core material, wireline logs, high resolution seismic and outcrop studies. These data gathering techniques are further discussed in Sections 5.3 and 2.2. 

Having gathered and evaluated relevant reservoir data it is desirable to present this data in a way that allows easy visualisation of the subsurface situation. With a workstation it is easy to create a three dimensional picture of the reservoir, displaying the distribution of a variety of parameters, e.g. reservoir thickness or saturations. All realisations need to be in line with the geological model. 

Maps can be created by hand or by computer mapping packages. The latter has become standard. Nevertheless, care should be taken that the mapping process reflects the geological model. Highly complex areas may require considerable manual input to the maps which can subsequently be digitised. 

At the development planning stage, a reservoir mode/will have been constructed and used to determine the optimum method of recovering the hydrocarbons from the reservoir. The criteria for the optimum solution will most likely have been based on profitability and safety. The model Is Initially based upon a limited data set (perhaps a seismic survey, and say five exploration and appraisal wells) and will therefore be an approximation of the true description of the field. As development drilling and production commence, further data is collected and used to update both the geological model (the description of the structure, environment of deposition, diagenesis and fluid distribution) and the reservoir model (the description of the reservoir under dynamic conditions). 

The final outcome will be a geological model that is more or less accurate and that can be used for the final design using simulation models. 

Pawar R.J., Zhang D., et al. Preliminary geologic modeling and flow simulation study of C02 sequestration in a depleted oil reservoir. NETL Carbon Sequestration Conference Proceedings. 

Identification of high risk areas through a program to assist States in conducting surveys to identify these areas, and through the development of predictive geological models. 

Plumlee, G., 1994b, Environmental geology models of mineral deposits. Society of Economic Geologists Newsletter 16,5-6. 

FIGURE 3.6 Point-bar geologic model showing the influence of a sequence of rock textures and structures in a reservoir consisting of a single point-bar deposit on horizontal permeability, excluding effects of diagenesis. (Modified after Ebanks, 1987.)... 

DE Kemp, E.A. 2007. 3-D geological modelling supporting mineral exploration. In Goodfellow, W.D. (ed) Mineral Deposits of Canada A Synthesis of Major Deposit-types, District Metallogeny, the Evolution of Geological Provinces, and Exploration Methods. Geological Association of Canada, Mineral Deposits Division Special Publication, 5, 1051-1061. 

In addition to geological modelling, geochronological data has significant implication for diamond exploration. A northern Alberta diamond window occurs... 

Agterberg, F. P. (2001). Multifractal simulation of geochemical map patterns. In Geologic Modeling and Simulation Computer Applications in the Earth Sciences (D. F. Merriam and J. C. Davis, eds.), pp. 31—39. Plenum Press, New York. 

Geological models are an independent entity and an essential part of hydrological models. Geological models deal with rock sequences (candi-... 

New and unconventional resources are all other types of deposits, typically inferred from geological modelling or identified but not presently being considered technically or economically feasible to exploit. 

Current estimates of the available reserves and further resources of uranium and thorium, and their global distribution, are shown in Figs. 5.44-5.50. The uraruum proven reserves indicated in Fig. 5.44 can be extracted at costs below 130 US /t, as can the probable additional reserves indicated in Fig. 5.45. Figure 5.46 shows new and unconventional resources that may later become reserves. They are inferred on the basis of geological modelling or other indirect information (OECD and IAEA, 1993 World Energy Council, 1995). The thorium resource estimates are from the US Geological Survey (Hedrick, 1998) and are similarly divided into reserves (Eig. 5.47), additional reserves (Fig. 5.48) and more speculative resources (Fig. 5.49). The thorium situation is less well explored than that of uranium the reserves cannot be said to be "economical", as they are presently mined for other purposes (rare earth metals), and thorium is only a byproduct with currently very limited areas of use. The "speculative" Th-resources may well have a similar status to some of the additional U-reserves. 

There are many ways to analyse hydrocarbon gas data with no one particular method being correct or incorrect. Common sense and a deterministic approach to sound geologic models are the best guidelines. Integration with other data such as structure, lithology, soil types and hydrogeology, to name a few, can be most fruitful. 

Lindsay, N.G., Murphy, F.C., Walsh, J.J. and Watterson, J, 1993. Outcrop studies of shale smears on fault surfaces. In S. Flint and A.D. Bryant (Editors), The Geological Modelling of Hydrocarbon Reservoirs and Outcrop Analogues. Int. Assoc. Sediment., 15 113-123. 

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