Page 242 - Geology and Geochemistry of Oil and Gas

MODELS OF STATIC GEOLOGIC SYSTEMS 209
(facilities). This chart also contains the feedback, which provides improvement of
theoretical foundations for the simulation of geologic systems.

11.2. MODELS OF STATIC GEOLOGIC SYSTEMS

With increasing depth of exploration, one of the major problems is the estimation
of influence of natural factors (total overburden, pore (fluid) and effective pressures,
reservoir pressure, formation temperature, lithology, pore space geometry, etc.) on
the properties of sedimentary rocks and formation fluids (lithofluidal system). The
lithofluidal system can be defined as follows:
Lithofluidal system is the well-organized natural assembly of interacting solid, liquid and
gaseous elements of lithosphere having common development history and a distinguishing
set of physical and chemical properties, which manifest themselves both individually and
jointly.
Mathematical models of the processes which describe the influence of pressure,
temperature, and structural and lithological factors on the properties of sedimentary
rocks and formation fluids can be presented using two approaches: deterministic
(analytical) and probabilistic (statistical). Both of these approaches are mutually
dependent and their combination enables the generalization of studied processes.
Statistical methods can be used only in the case of the existence of sufficient data.
These data are obtained either at the stage of completion of exploration or during
subsequent development of a deposit. Obtaining the representative data can be very
expensive. Therefore, new procedures should be developed for prediction of rock and
fluid properties when data are sparse. Such studies are especially appropriate for the
exploration and development of oil and gas fields, which occur at great depths or in
harsh environments. At the latter case, the problems of drilling, coring, testing, and
logging do not allow the acquisition of reliable data for the evaluation of reservoir
rock and caprock properties, and formation fluid properties, especially at the early
stage of exploration.
The main principles used in mathematical simulation are as follows:
1. The most complete quantitative characteristics of the geological, geophysical,
and geochemical parameters are described by their statistical distributions.
2. The distributions of geological, geophysical, and geochemical parameters are
simulated on the basis of their mathematical descriptions (models), which may be
probabilistic or deterministic.
3. In the case of scarcity of data, the artificial distributions of model input data are
formed by means of their interval-probable presentation, and the Monte Carlo
technique is used for plotting such distributions.
4. For the purposes of predicting properties of rocks and formation fluids, simu-
lation of statistical distributions is required on the basis of models with variable
input data depending upon changes in the regional geologic environments.
5. For the purposes of identification of formations, simulation of more than one
statistical distribution and the determination of the cut-off points for the sim-
ulated parameters (which allows strata classification) are required.