Modelling facility for field-average average formation pressure
at any time moment as response to production flowrates history, which in case of MBO fluid takes form:| LaTeX Math Block |
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| anchor | MatBal |
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A_e \, h_e \int_{p_i}^p \phi_e(p) \, c_t(p) \, dp = \Delta Q (t) = \phi_n(p) = \frac{B_o - R_s \, B_g}{1- R_s \, R_v} \cdot F_O
+\frac{ B_g - R_v \, B_o}{1- R_s \, R_v} \cdot F_G
+B_w \, F_W |
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| \phi_n = \exp \left[ c_\phi \, (p-p_i) \right] \approx 1 + c_\phi \, (p-p_i) + 0.5 \, c^2_\phi \, (p-p_i)^2 |
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| F_O = V_\phi^{-1} \, \delta \, Q_O + F_{Oi} |
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| F_{Oi} = \frac{s_{oi}}{B_{oi}} + \frac{R_{vi}\, s_{gi}}{B_{gi}} |
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| \delta \, Q_O = - Q^{\uparrow}_O |
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| F_G = V_\phi^{-1} \, \delta \, Q_G + F_{Gi} |
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| F_{Gi} = \frac{R_{si}\, s_{oi}}{B_{oi}} + \frac{ s_{gi}}{B_{gi}} |
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| \delta \, Q_G = Q^{\downarrow}_ |
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t(t)t(t) +G + Q^{\downarrow}_{GCAP} |
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| F_W = V_\phi^{-1} \, \delta \, Q_W + F_{Wi} |
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| F_{Wi} = \frac{ s_{wi}}{B_{wi}} |
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| \delta \, Q_W = Q^{\downarrow}_ |
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{GC}(t)W - Q^{\uparrow}_W + Q^{\downarrow}_{WAQ} |
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(t)where
initial formation pressure\Delta Q | --uriencoded--Q%5e%7B\uparrow%7D_O(t) |
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full-field cumulative reservoir fluid balance A_e | drainage areaQ^{\uparrow}_t| --uriencoded--Q%5e%7B\uparrow%7D_G(t) |
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full-field cumulative offtakesh_e | effective formation thickness averaged over drainage areaQ^{\downarrow}_t| --uriencoded--Q%5e%7B\uparrow%7D_W(t) |
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full-field cumulative intakes_e(p)effective porosity as function of formation pressure p| --uriencoded--Q%5e%7B\downarrow%7D_G(t) |
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| body | --uriencoded--s_%7Bgi%7D |
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Q^{\downarrow}_{GC}(t) | cumulative volumetric inflow from Gas Cap Expansion| --uriencoded--Q%5e%7B\downarrow%7D_%7BWAQ%7D(t) |
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| Cumulative water influx from Aquifer Expansion by the time moment |
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| body | --uriencoded--s_%7Boi%7D |
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| initial oil saturation: | LaTeX Math Inline |
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| body | --uriencoded--s_%7Boi%7D = 1 - s_%7Bwi%7D - s_%7Bgi%7D |
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| body | --uriencoded--Q%5e%7B\downarrow%7D_%7BGCAP%7Dt) |
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| Cumulative gas influx from Gas Cap expansion by the time moment |
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cttotal compressibility as function of formation pressure (t)Q^{\downarrow}_{WAQ}(t) | cumulative volumetric inflow from Aquifer Expansion
The MatBal equation
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is often can be complemented by constant
PI model of Bottom-Hole Pressure ( for
producers and
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| body | p^{\downarrow}_{wf}(t) |
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for
injectors):| LaTeX Math Block |
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| anchor | BHP_PROD |
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| p^{\uparrow}_{wf, k}(t) = p(t) - {J^{\uparrow}_k}^{-1} \cdot \frac{dQ^{\uparrow}_k}{dt} |
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| anchor | BHP_INJ |
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| p^{\downarrow}_{wf, \, j}(t) = p(t) - {J^{\downarrow}_j}^{-1} \cdot \frac{dQ^{\downarrow}_j}{dt} |
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| where | where |
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| body | p^{\uparrow}_{wf, \, k}(t) |
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\,
In practice there is no way to measure the external influx
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| body | Q^{\downarrow}_{GC}(t) |
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and
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| body | Q^{\downarrow}_{AQ}(t) |
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so that one need to model them and calibrate model parameters to fit available data on
production flowrates history and
formation pressure data records.
There is a list of various analytical aquifer Aquifer Drive and Gas Cap drive models Drive models which are normally based on the relationsrelated to pressure dynamics
:
Expansion Expansion FQ^{\downarrow}_{GC}(p(t)) |
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| Q^{\downarrow}_{AQ}(t) = |
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FQ^{\downarrow}_{AQ}(p(t)) |
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...
which closes equation
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for the pressure .Approximations
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In some specific cases equation
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can be explicitly integrated with the accuracy sufficient for practical applications:\{ | --uriencoded--c_t = c_\phi + c_ |
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e = { const}, \ c_t = {\rm const} \}| fluid%7D = %7B\rm const%7D |
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t = c_r + \frac{1}{p} frac{1}{p} |
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| p(t) = p_i + \frac{\Delta Q(t)}{V_ |
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e | | LaTeX Math Block |
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| p(t) = p_i \exp \left[ \frac{\Delta Q(t)}{V_ |
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e \cdot c_t where
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is Cumulative Voidage Replacement Balance (CVRB):| LaTeX Math Block |
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| \Delta Q = - \frac{B_o - R_s \, B_g}{1- R_s \, R_v} \cdot \, Q^{\uparrow}_O + \frac{ B_g - R_v \, B_o}{1- R_s \, R_v} \cdot \, \left( Q^{\downarrow}_G - Q^{\uparrow}_G + Q^{\downarrow}_{GCAP} \right) + B_w \, \left( Q^{\downarrow}_W - Q^{\uparrow}_W + Q^{\downarrow}_{WAQ} \right) |
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The above approximations sometime allow using simple graphical methods for rough estimation of drainage volume
and associated Hydrocarbon Reserves.See Also
...
Petroleum Industry / Upstream / Production / Subsurface Production / Field Study & Modelling / Production Analysis / Material Balance Analysis (0D or MatBal)MatBal)
[ Material Balance Pressure Plot ][ FMB Pressure @model]
[ Derivation of Material Balance Pressure @model ]
[ Modified Black Oil fluid @model (MBO) ]
