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Definition
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A set of mathematical models relating production rate to the bottomhole pressure and offset injection rate.
In case the bottom-hole pressure data is not available it is considered constant over time.
The CRM is trained over historical records of production rates, injection rates and bottom-hole pressure variation.
The major assumptions in CRM model are:
- productivity index of producers stays constant in time
- drainage volume of producers-injectors system is finite and constant in time
- total formation-fluid compressibility stays constant in time
Application
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- Assess current production performance
- current distribution of recovery against expectations
- current status and trends of recovery against expectations
- current status and trends of reservoir depletion against expectations
- current status and trends of water flood efficiency against expectations
- compare performance of different wells or different groups of wells
- Identify and prioritize surveillance opportunities
- Identify and prioritize redevelopment opportunities
Advantages
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- fast-track
- based on the robust input data
- does not involve full-field 3D dynamic modelling and associated assumptions
Limitations
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Does not pretend to predict reserves distribution as dynamic model does |
Only provides hints for misperforming wells and sectors which need a further focus |
Only provides hints for misperforming wells and sectors which need a further focus |
Can only be tuned for injector-producer pairing with a rich history of injection rates variations |
Can only work at long times and only in areas with limited drainage volume |
Technology
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CRM trains linear correlation between variation of production rates against variation of injection rates with account of bottom-hole pressure history in producers.
against material balance and require current FDP volumetrics, PVT and SCAL models.
The CRM has certain specifics for oil producers, water injectors, gas injectors and field/sector analysis.
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CRM – Single-Tank Capacitance Resistance Model
The CRM model is trying
The simulation is based on the following equation:
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q^{\uparrow}(t) = f \, q^{\downarrow}(t) - \tau \cdot \frac{ d q^{\uparrow}}{ dt } - \beta \cdot \frac{d p_{wf}}{dt} |
where
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The
and constants are related to some primary well and reservoir characteristics: LaTeX Math Block |
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\beta = c_t \, V_\phi |
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\tau = \frac{\beta}{J} = \frac{c_t V_\phi}{J} |
where
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Total formation compressibility is a linear sum of reservoir/fluid components:
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c_t = c_r + s_w c_w + s_o c_w + s_g c_g |
where
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The first assumption of CRM is that productivity index of producers stays constant in time:
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J = \frac{q_{\uparrow}(t)}{p_r(t) - p_{wf}(t)} = \rm const |
which can re-written as explicit formula for formation pressure:
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p_r(t) = p_{wf}(t) + J^{-1} q_{\uparrow}(t) |
The second assumption is that drainage volume of producers-injectors system is finite and constant in time:
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V_\phi = V_{rocks} \phi = \rm const |
The third assumption is that total formation-fluid compressibility stays constant in time:
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c_t \equiv \frac{1}{V_{\phi}} \cdot \frac{dV_{\phi}}{dp} = \rm const |
which can be easily integrated:
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V_{\phi}(t) =V^\circ_{\phi} \cdot \exp \big[ - c_t \cdot [p_i - p_r(t)] \big] |
where
is field-average initial formation pressure, is initial drainage volume,...
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is drainage volume at time moment . LaTeX Math Block |
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\frac{dV_{\phi}}{dp} = c_t \, V_{\phi} \ \cdot |
The change in drainage volume
is leading to formation pressure variation LaTeX Math Block |
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c_t \equiv \frac{1}{V_{\phi}} \cdot \frac{dV_{\phi}}{dp} = \frac{1}{V_{\phi}} \cdot \frac{1}{p_i - p_r(t) } \cdot \Bigg[ \int_0^t q_{\uparrow}(\tau) d\tau - f \int_0^t q_{\downarrow}(\tau) d\tau \Bigg] = \rm const |
The last equation can be rewritten as:
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\int_0^t q_{\uparrow}(\tau) d\tau - f \int_0^t q_{\downarrow}(\tau) d\tau = c_t \, V_\phi \, [p_i - p_r(t)] |
and differentiated
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q_{\uparrow}(\tau) = f q_{\downarrow}(\tau) - c_t \, V_\phi \, \frac{d p_r(t)}{d t} |
and substituting
from productivity equation LaTeX Math Block Reference |
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: LaTeX Math Block |
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q_{\uparrow}(\tau) = f q_{\downarrow}(\tau) - c_t \, V_\phi \, \bigg[ \frac{d p_{wf}(t)}{d t} + J^{-1} \frac{d q_{\uparrow}}{d t} \bigg] |
which leads to
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.The target function is:
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E[\tau, \beta, f] = \sum_k \big[ q^{\uparrow}(t_k) - \tilde q^{\uparrow}(t_k) \big]^2 \rightarrow \min |
The constraints are:
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\tau \geq 0 , \quad \beta \geq 0, \quad 0 \leq f \leq 1 |
CRMP – Multi-tank Producer-based Capacitance Resistance Model
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q^{\uparrow}_j (t) = \sum_i^{n_i} f_{ij} q^{\downarrow}_i(t) - \tau_j \cdot \frac{ d q^{\uparrow}_j}{ dt } - \beta_j \cdot \frac{d p_j}{dt} |
The target function is:
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E[\tau, \beta, f] = \sum_k \sum_j \big[ q^{\uparrow}_j(t_k) - \tilde q^{\uparrow}_j(t_k) \big]^2 \rightarrow \min |
The constraints are:
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\tau_j \geq 0 , \quad \beta_j \geq 0, \quad f_{ij} \geq 0 , \quad \sum_i^{N^{\uparrow}} f_{ij} \leq 1 |
ICRM – Multi-Tank Integrated Capacitance Resistance Model
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Q^{\uparrow}_j (t) = \sum_i^{n_i} f_{ij} Q^{\downarrow}_i(t) - \tau_j \cdot \big[ q^{\uparrow}_j(t) - q^{\uparrow}_j(0) \big] - \beta_j \cdot \big[ p_j(t) - p_j(0) \big] |
The target function is:
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E[\tau, \beta, f] = \sum_k \sum_j \big[ Q^{\uparrow}_j(t_k) - \tilde Q^{\uparrow}_j(t_k) \big]^2 \rightarrow \min |
The constraints are:
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\tau_j \geq 0 , \quad \beta_j \geq 0, \quad f_{ij} \geq 0 , \quad \sum_i^{N^{\uparrow}} f_{ij} \leq 1 |
See Also
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Petroleum Industry / Upstream / Production / Subsurface Production / Field Study & Modelling / Production Analysis
References
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Capacitance-Resistivity Model @model
References
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https://doi.org/10.2118/147344-MS
https://doi.org/10.2118/177106-MS
RAFAEL WANDERLEY DE HOLANDA, CAPACITANCE RESISTANCE MODEL IN A CONTROL SYSTEMS FRAMEWORK: A TOOL FOR DESCRIBING AND CONTROLLING WATERFLOODING RESERVOIRS, 2015.pdf
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