Natural Oil Depletion
The EUR during the natural oil depletion can be assessed with the following equation (see NDR @model for derivation):
| (1) | {\rm EUR}_O = \frac{Q_O}{V_O} = \frac{ (p_i - p_{wf}) \, c_t}{(1-s_{wi})\, B_o} = \frac{ (p_i - p_{wf}) }{(1-s_{wi})\, B_o} \, \big( c_r + s_{wi} c_w + (1-s_{wi})c_o \big) |
where
p_{wf_ \, {\rm min}} | minimal flowing bottom-hole pressure |
|---|---|
p_i | initial formation pressure |
B_o | formation volume factor for oil, |
Q_o | cumulative oil production |
V_o | STOIIP |
s_{wi} | initial water saturation in oil pay |
c_t | total compressibility |
For the naturally flowing wells the bottom hole pressure under flowing conditions can be roughly assed by homogeneous multiphase pipe flow model assessed as:
| (2) | p_{wf} = p_s + \rho_g \, g\, h + \bigg( 1- \frac{\rho_g}{\rho_o} \bigg) \, p_b |
where p_s – tubing-head pressure defined by the production gathering system, h – is the true vertical depth at formation top, \{ \rho_o, \, \rho_g \} – oil and gas densities, p_b – bubble-point pressure.
Natural Gas Depletion
The Expected Ultimate Recovery during the natural gas depletion can be assessed with the following formula:
| (3) | EUR_{GD} = \frac{Q_g}{V_g} = 1- \frac{p_{wf}}{p_i} |
See also
Petroleum Industry / Upstream / Production / Field Development Plan / Recovery Methods
[ NDR @model ]