3.1. Productive formation.
Development of deposits at natural modes (drives) does not last long, 3-5 years. For further enhancement of oil recovery we should use the systems and methods of development of deposits with stimulation of formation.
Under the system of oil fields OF and oil deposits OD development it is considered to understand the form of the organization of oil movement in the layers to producing wells. The development system of OF(oil fields) is determined by: the order of the operational objects input of multilayer fields into development; borehole grid of objects; the rate and input procedure of the wells’ operation; the ways of balance regulation and use of reservoir energy.
There are the development systems of single-layer and multilayer deposits. One of the basic concepts, used in the development of oil deposits, is the production facility.
Under the basic multilayer productive formation of oil field is understood a reservoir, deposit, that is being developed by independent grid.
If several deposits, reservoirs are developed by single grid jointly, we are talking about the development of production facility.
Thus, production facility or productive formation is a set of elementary objects (deposits, reservoirs), developed by an independent grid simultaneously. Multilayer field can contain several production facilities, which are developed simultaneously. If the field is multilayer, there will be pointed out the main production facility that is to develop at first, after the studying of geological structure of formations, pool-reservoir properties, establishment of geological reserves categories. The development of the remaining formations can be started later, when the main part of the recoverable reserves of the main production facility are mined out. If the wells of the main production facility are transferred to another formation, this formation is called return. Moreover, both formations can be used fully or partially by the single well system.
Further, we will observe the systems and indicators of the production facilities, but not the whole field.
3.2. The reservoir recovery and oil recovery factor (orf).
An indicator of the drive effectiveness is reservoir recovery that is the degree of oil recovery completeness. Reservoir recovery is characterized by the oil recovery factors (ORF).
Project (predictable, end) ORF ηк is reasoned and planned with the help of the calculation of reserves and the planning of field development. After its justification, oil recoverable reserves N are planned and approved.
Where G – geological (balance) reserves
When the field development happens on the base of natural recovery drives, the end ORF ηк can have the following meanings:
water drive к =0,5÷0,8
gas cap drive к =0,1÷0,4
dissolved gas drive к =0,05÷0,3
gravity drive к =0,1÷0,2
Current ORF is defined by the following ratio
,
Where Qтек(t ) - current oil production, such as year oil production, Qнак(t) - cumulative production – the quantity of oil, extracted from the beginning of the development , t - time of field development. Current oil production, depending on the time of deposit development and the applied enhanced oil recovery methods, can increase and decrease over the time. Cumulative production can only grow, thus, the current ORF over the time increases (fig.3.1).
Fig. 3.1.Current ORF changing over the time.