9.1. Filtration flows’ direction changing.

The technology of this method considers that water injection to the injection wells of the production facility periodically changes. The first stage involves only injection wells, other wells don't work (fig.9.1.a). At the second stage the injection to these wells is terminated and transferred to the others (fig. 9.1.b). As a result, the filtration flows direction changing occurs.

The physical essence of the process considers the following: under normal flooding due to the difference of the coefficients of oil and water mobility, instability of the displacement process, heterogeneity of reservoir properties, there is formed the bypassed oil. When you change the injection front there are formed the pressure differentials, changing in size and direction, in the reservoir; the injected water embeds in the stagnant low-permeability zones and displaces oil from them to the zones of intensive water movement. The volume of water injection along the front of displacement is recommended to distribute proportionally to the remaining oil saturation (respectively to the decreasing water saturation). The changing of filtration flows direction is achieved by means of additional deposits’ cutting into blocks, by the application of spot flooding, redistribution of extraction and injection between the wells.

In figure 9.1. there is represented one of the possible schemes of filtration flows’ changing.

Fig. 9.1. The scheme of filtration flows’ changing. а) the performance of the first group injection wells, б) the first group wells’ shut-down, the performance of the second group injection wells, 1 – flowing injection wells, 2- idle injection wells, 3 –producing wells.

The method is producible it requires only a small power reserve of the pumping stations and active flooding system. For this method there are used cross-cutting rows, the combination of edge water flooding and circle water flooding. The application of this method allows to maintain the achieved oil production rate, to reduce the current water cut level and to increase the sweep flooding [3].

9.2. Forced fluid withdrawal (ffw)

Forced fluid withdrawal considers gradual increase of producing wells output. The essence of a method consists in the creating of high pressure differentials by depression increasing, hence, there is the reduction of bottomhole pressure of the producing wells and increasing of the injection wells. The residual bypassed oil, oil lenses, dead end and stagnant zones, low-permeability interlayers are involved into development of heterogeneous high-watered formations. The conditions of method application:

1) Output water cut is not less than 90-95% (The beginning of the closing stage of the development);

2) High coefficients of wells’ effectiveness at the beginning of the field operation;

3) The reservoir is stable under the conditions of bottomhole pressure decrease (it is not destructed), the injection pressure shouldn’t exceed rock’s breakdown point;

4) the casing string is nonfault, water cross flows are absent from the neighboring horizons;

5) The flow capacity of the production system is enough to apply forced fluid withdrawal.

For the application of the method it is recommended to collect and analyze the information about the well production activity, namely: the liquid and oil production rates, water cut factor, bottom-hole pressures of producing and injection wells (hence the rates of productivity and injectivity), the composition of the salts in the injected water (hence, the proportion of the outside water). Liquid production rates are prescribed by the maximum oil production rate of every selected well to use the method.

To apply the method of the forced fluid withdrawal is necessary to compare different ways of oil deposits development with the oil of different viscosity. These options are differed in forcing dynamics (increase) of fluid withdrawal at the constant rational maximum bottom-hole pressure of the injection wells and rational minimum bottom-hole pressure of the producing wells.

Technically, forced withdrawal is fulfilled by the use of electric pumps with more supply, sucker-rod pumps operating at full load.

To increase the inflow and injectability profiles it is necessary to provide the works on the injectability profile changing of the injection wells and inflow profile of the producing wells before the use of the method of forced fluid withdrawal (paragraph 8.6). It is recommended to supply acid treatment, squeeze job to eliminate the cross- flow of fluid from the overlying strata.