3.6.5. Development stages of the production facilities (oil fields)

The process of the development of a production facility of oil fields can be divided into four stages I, II, III, IV, pictures, 3.4, 3.5.

Fig.3.4. Development stages of production facilities

Fig.3.5. Changes dynamics of development rates z(t) and (t)

The I^st stage - drilling of production facility of the field, putting the wells into operation, oil production lasts 4-5 years.

The II^nd stage is characterized by a maximum oil production, growth of water cut, conversion of wells to pump operation.

The III^rd stage - there is a sharp decrease of current oil production, growing of water production, reduction of firm wells due to watering. This stage is the most difficult to develop, its main task is slow decrease of oil production rate. At the third stage there are applied enhanced oil recovery methods.

The first three stages are the main development stages.

The IV^th stage is characterized by slowly falling oil production rate, high, slowly increasing watering of production, reduction of the firm wells.

3.7. Types of water flooding

Depending on the location of injection wells in relation to the oil deposit there are edge water flooding, boundary and circle water flooding. A combination of these types of flooding is usually used for many fields.

3.7.1. Edge water flooding.

Edge water flooding is applied if the weak activity of the formation edge waters do not compensate the deposit production rate. Reservoir pressure in deposits is reduced and to replenish energy resources edge water flooding is used. Injection wells are behind the external contour of oil content. The location of injection wells depends on the distance between the external and internal contours of oil content; the geological conditions of bedding and pool-reservoir properties.

Edge water flooding is used to develop homogeneous deposits with low-viscosity oils with small oil-water zone (WOZ), which is located between the inner and outer contours of oil content. Also, it is used for not large pure oil zone (POZ). The distance between the wells is 500-600 m, width of the deposit is 2.5-3 km, the grid density S_C=25÷30 ha/well

Fig. 3.6. Wells’ location at edge water flooding. 1 – injection wells at edge water flooding, 2 – producing wells, 3 – inner oil pool outline, 4 – outer oil pool outline.

The disadvantages of edge water flooding are losses of injected water in the edge-water zone.

3.7.2. Boundary water flooding

This method is the method of reservoir pressure maintenance by water injection in the boundary zone, oil part of the reservoir. The injection wells are placed between the external and internal contours of oil content. It is applied when the permeability is reduced in edge water zone (aquifer) of the reservoir or in the situation of poor hydrodynamic connection between water and oil reservoir parts (Fig. 3.7), and also it is used when the oil-water zone between the external and internal contours of oil content is small. Method of boundary water flooding, in comparison with the others, more intensive methods cannot provide maximum production rate for a brief period of time, but allows to keep a relatively high and stable production rate for a longer period of time.

Fig. 3.7. Boundary water flooding. 1 – Injection wells of boundary water flooding, all the rest symbols are the same as in fig. 3.6.