Page 40 - Geology and Geochemistry of Oil and Gas

SYSTEMS APPROACH IN PETROLEUM GEOLOGY 17
Following the general scheme of scientific knowledge (Table 1.4), a schematic
image of the construction of geologic knowledge or geologic theory was developed
(Fig. 1.2).
Subsystem T (Theory) includes a priori geologic concepts covering such funda-
mental properties of geologic systems as their structure, material composition, dy-
namics (function), and history.
Subsystem M (Method) is subdivided into a number of purely geologic study
techniques and those adapted from other scientific disciplines.
Subsystem F (Fact) is the derivative of two subsystems described above and
includes results of experimental and field observations (measurements) conducted in
various ways according to a priori set of geologic concepts.
Subsystem S (Subject) is the assignment of goal for the study of specific geologic
bodies. The primary models of geologic bodies obtained as a result of direct ob-
servations and measurements (maps, profiles, cross-sections, tables, graphs, etc.)
should be understood and accepted as a subject in geology.
Subsystem R (Result) contains the newly derived knowledge that either enters
directly as a practical implementation or serves as a further development of the-
oretical and methodological concepts (a posteriori theoretical concepts).
The system of oil and gas reserves estimation may serve as an example of con-
struction of geologic knowledge system. It includes the following five subsystems:
(1) Geologic conditions of subsurface reservoir occurrence: type of traps, structural
elements, depth of occurrence, type of reservoir, type of reservoirs, type of
sealing rocks, type of hydrocarbon accumulation, and type of formation fluids.
(2) Reservoir structure and parameters: folding and faulting features, porosity,
permeability, fluid saturation, wettability of rocks, and compressibility.
(3) Reservoir drive mechanism: solution gas drive, gravity drainage, water drive,
gas-cap drive, compaction drive, or combination drive.
(4) Hydrocarbon reserves estimation: volumetric, statistical and material balance
techniques.
(5) Evaluation of effectiveness of reserve estimation: accuracy of estimate, reliability
of reserves, proportion of various reserve categories, and value of reserves.
Thus, the in-place and recoverable reserves are estimated based on the detailed
simulation of oil and gas reservoir. The estimated amount of reserves is used for
justification of capital investments in oil and gas field development and production.
The reserve estimation system is a key step dictating the transfer from exploration to
production. Geologic system ‘‘oil and gas reservoir’’ at the stage of production is
transformed into geologic-engineering system (‘‘producing oil and gas reservoir’’).