4.2.4. Pollard model.

Fractured - porous formation is represented in the form of three areas. The first one describes the system of fissures in the bottom-hole zone, the second is the system of fissures and pore channels that are far from the well bottom, the third area corresponds to the matrix, blocks and porous medium. There is the cross-flow between the areas. The total pressure drop in the reservoir is the sum of the pressure drops in each area and it happens due to the volume of compressibility of the appropriate areas. The system parameters are determined by the interpretation of the pressure recovery curves (PRC) results [12]

Fig. 4.5. Pollard model. 1–fissures area in the bottom-hole, 2- fractured-porous reservoir area, 3 – matrix, porous reservoir.

Each of the above models tends to reflect the geological features of the formation structure and physical processes occurring in the reservoir under the condition of liquids filtration. Each model has its advantages and disadvantages.

4.2.5. Models use peculiarities of the reservoirs of complex structure.

Pollard model.

During the primary formation exposing in the bottom-hole area there are formed the man-caused fissures that are used to provide the fluid flow after the well completion. The further from the bottom-hole area, the less volume of the fissures in the formation. The formation, in this case, corresponds to its non-disturbed, natural state. The size of each of these three areas depends on the lithological composition and reservoir properties.

Kazemi model and multi-layer formation, Serra model.

The representation of the reservoir in the form of a stratified formation separation in the high-permeable interlayers and low-permeable interlayers or in fissures with horizontal separation by the blocks is based on the laboratory, geophysical and hydrodynamic methods of well testing. Well distance, depending on the well grid density, reaches hundreds of meters. The presence or absence of hydrodynamic connection between the fissures and matrix, high-permeable and low-permeable interlayers can be broken. It is practically impossible to determine this breaking, that’s why for the changes distribution of pool-reservoir properties the methods of interpolation and probability theory methods are used. That’s why, in the process of planning and forecasting of the development parameters the inevitable nonconformance will appear with the actual parameters.

Warren-Ruth model.

In this model there should be known the size of porous blocks, containing oil reserves. There are the works of definition of the geometrical sizes of the blocks according to the field geophysical researches.

Barenblatt-Zheltov model.

The model of dual environments is attractive by mathematical description. But, unfortunately, it is difficult to understand and does not conform with a particular geological structure of the deposit.

In all the observed models with dual pool-reservoir system there is something in common: namely, fissures, high-permeable interlayers are more permeable. The blocks, the matrix, the low-permeable interlayers have greater capacitive ability (porosity) which contains basic, a large proportion of recoverable hydrocarbons. During the process of oil recovery the fluid flow to the bottom of the producing wells occurs through the fractures, high-permeable interlayers. The matrix, the blocks, low-permeable interlayers feed the objects, the environment with greater permeability in the result of cross-flow of the fluids.

Proper choice of the formation model significantly influences on the development of operation facility in general, and on the choice of the well recovery drive. If actual and calculated parameters of the chosen model differ, it indicates about nonconformance of the chosen model of the formation geological structure.

On the other hand the correctly chosen model allows to predict accumulated and current production rate, injection capacity, watering, etc. We should notice that within one operational object there may be implemented different models.