3.6.2. Borehole grid. Wells’ density.
Under the borehole grid there is considered the distances between the wells, their location relative to each other, the rate and wells procedure order into operation. Wells can be situated according to the even and uneven grid, also a row grid.
Well density is determined:
,
[Sc]=га/скв
S – oil productive area; Sc changes in the range of 10 ÷ 60 га/скв.
n – total wells number.
n=nд+nн
nд – a number of producing wells, nн - a number of injection wells.
Except wells density there is the producing wells’ density
The physical sense of wells density is the area of oil-saturated reservoir per one recovery well.
It is proved practically that the wells density affects the oil recovery. This impact is greater, the more intermittent and inhomogeneous the layers are, the worse lithologic-physical properties of the reservoir, the higher oil viscosity is. The well grid compaction means the increasing of recovery wells number at a constant area of development, thus the grid wells densities S, Sc decrease.
The wells grid compaction in heterogeneous -lenticular formations increases oil recovery. In the very case, the wells density choice depends on particular physical-lithological conditions.
3.6.3. Krylov’s parameters. Compensation factor. Water cut factor.
Krylov’s parameter NКР is the ration of recoverable reserves N to the total wells’number n:
NКР = N/n; [NКР] = tons/well.
The physical meaning of the Krylov’s parameter is the amount of recoverable reserves per recovery well. Roughly speaking, that is what is desired to recover from one well.
Let nр be a number of backup wells that are drilled in addition to the firm wells with the purpose of engaging in the development of the reservoir parts that have not been developed before, because of the previously unknown features of geological reservoir structure in the process of drilling (lithological heterogeneity, tectonic disturbances), non-Newtonian properties of oil. To estimate the number of backup wells in relation to the project operational wells there is used the following parameter:
Compensation factor is determined by the ratio of the volume of injected liquid into the formation for a certain period of time Vзак(t), for example, from the beginning of development or for the year to the volume of the extracted liquid Vдоб(t) for the same period of time.
Water cut factor is defined as the ratio of the volume of produced, extracted water to the total volume of extracted liquid or it can be the ratio of water rate to the total production rate of water and oil. It is determined after the separation of the products on the surface.
,
(3.1)
Vж=Vв+Vн , qж=qв+qн
Vж , Vв, ,Vн – volumes of the extracted liquid, water and oil for the certain period of time. qж , qв,,qн – production rates of liquid, water and oil.
3.6.4. Oil fields development rates.
Development rate is determined as:
,
Where Qтек(t) is a current production rate, N – recoverable reserves.
Development rate from the remaining reserves.
There is connection between z(t) and (t).