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  1. Start with true UTRs 
    LaTeX Math Inline
    body\displaystyle p_{u, ik}(t)
    with the same LTR asymptotic
    LaTeX Math Inline
    body\displaystyle p_{u, ik}(t) \rightarrow \frac{t}{RS}
    .
  2. Select injector W0 
    1. Select producer W1
      1. Perform a convolution tests to account for the impact from {W2 .. WN} production and from {W-1 .. W-M} on to CTR_01
        LaTeX Math Inline
        bodyp_{u, 01}(t)
        LaTeX Math Inline
        body\displaystyle p^*_{u, 01}(t) = p_{u, 01}(t) + \sum_{i \neq 0 \in {\rm inj}} p_{u, i1}(t) \cdot q^{\downarrow}_i(t)
      2. Perform two convolution tests to account for the impact from {W2 .. WN} production on to DTR_11
        LaTeX Math Inline
        bodyp_{u, 11}(t)
         and CTR_01
        LaTeX Math Inline
        bodyp_{u, 01}(t)
        :
        • Test #1 – DTR_11
          • Calculate interfering DTR_11: 
            LaTeX Math Inline
            body\displaystyle p^*_{u, 11}(t) = p_{u, 11}(t) + \sum_{k \neq 1 \in {\rm prod}} p_{u, k1}(t) \cdot q^{\uparrow}_k(t)
            , meaning that all injectors W0 are shut-down and all producers were working with their historical rates 
            LaTeX Math Inline
            bodyq^{\uparrow}_k(t)
            , except producer W1 which is working with unit-rate
        •  Test #2 – CTR_01
          • Calculate interfering CTR_01: 
            LaTeX Math Inline
            body\displaystyle p^*_{u, 01}(t) = p_{u, 01}(t) + \sum_{i \neq 0 \in {\rm inj}} p_{u, i1}(t) \cdot q^{\downarrow}_i(t)
            , meaning that all producers are shut-down and all injectors are working with their historical rates 
            LaTeX Math Inline
            bodyq^{\downarrow}_i(t)
            , except injector W0 which is working with unit-rate
      3. Calculate injection share constant
        LaTeX Math Inline
        body\displaystyle f_{01} = \frac{\dot p^*_{01}(t)}{\dot p^*_{11}(t)} \Bigg|_{t \rightarrow \infty}
         as LLS over equation: 
        LaTeX Math Inline
        body\displaystyle \dot p^*_{01}(t) = f_{01} \cdot \dot p^*_{11}(t)
    2. Repeat the same for other producers (starting from point 2a onwards)
  3. Repeat the same for other injectors (starting from point 2 onwards)
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titleDerivation


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Consider a pressure convolution equation for the well W1 with constant BHP in a multi-well system :

LaTeX Math Block
anchor1
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p_1(t) = p_i - \sum_{k \in {\rm prod}} \int_0^t p_{u,\rm k1}(t-\tau) dq^{\uparrow}_k(\tau) - \sum_{i \in {\rm inj}} \int_0^t p_{u,\rm i1}(t-\tau) dq^{\downarrow}_i(\tau) = \rm const

The time derivative is going to be zero as the BHP in producer W1 stays constant at all times:

LaTeX Math Block
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\dot p_1(t) = - \left( \sum_{k \in {\rm prod}} \int_0^t p_{u,\rm k1}(t-\tau) dq^{\uparrow}_k(\tau) \right)^\cdot - 
\left( \sum_{i \in {\rm inj}} \int_0^t p_{u,\rm i1}(t-\tau) dq^{\downarrow}_i(\tau) \right)^\cdot = 0


LaTeX Math Block
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\sum_{k \in {\rm prod}} p_{u,\rm k1}(0) \dot q^{\uparrow}_k(t) + 
\sum_{k \in {\rm prod}} \int_0^t \dot p_{u,\rm kk}(t-\tau) dq^{\uparrow}_k(\tau) = 
- \sum_{i \in {\rm inj}} p_{u,\rm i1}(0) \dot q^{\downarrow}_i(t) 
-  \sum_{i \in {\rm inj}} \int_0^t \dot p_{u,\rm i1}(t-\tau) dq^{\downarrow}_i(\tau) 

The zero-time value of DTR / CTR is zero by definition 

LaTeX Math Inline
bodyp_{u,\rm kj}(0) = 0, \ \forall k,j \in \mathbb{Z}
which leads to:

LaTeX Math Block
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\sum_{k \in {\rm prod}} \int_0^t \dot p_{u,\rm k1}(t-\tau) dq^{\uparrow}_k(\tau) = 
-  \sum_{i \in {\rm inj}} \int_0^t \dot p_{u,\rm i1}(t-\tau) dq^{\downarrow}_i(\tau) 

Let's separate producer W1 and injector W0 terms: 

LaTeX Math Block
anchorpre_eq
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 \int_0^t \dot p_{u,\rm 11}(t-\tau) dq^{\uparrow}_1(\tau) + \sum_{k \neq 1 \in {\rm prod}} \int_0^t \dot p_{u,\rm k1}(t-\tau) dq^{\uparrow}_k(\tau) = 
-  \int_0^t \dot p_{u,\rm 01}(t-\tau) dq^{\downarrow}_0(\tau)  - \sum_{i \neq 0 \in {\rm inj}} \int_0^t \dot p_{u,\rm i1}(t-\tau) dq^{\downarrow}_i(\tau) 


Consider a step-change in injector's W0 flowrate 

LaTeX Math Inline
body \delta q^{\downarrow}_0
 at zero time 
LaTeX Math Inline
body\tau = 0
, which can be written as 
LaTeX Math Inline
bodydq^{\uparrow}_1(\tau) = \delta q^{\uparrow}_1 \cdot \delta(\tau) \, d\tau
, leading to a step-change in production rate in producer  W1
LaTeX Math Inline
bodydq^{\uparrow}_1(\tau) = \delta q^{\uparrow}_1 \cdot \delta(\tau) \, d\tau
.

Substituting this to 

LaTeX Math Block Reference
anchorpre_eq
 leads to:

LaTeX Math Block
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\dot p_{u,\rm 11}(t) \delta q^{\uparrow}_1 + \sum_{k \neq 1 \in {\rm prod}} \int_0^t \dot p_{u,\rm k1}(t-\tau) dq^{\uparrow}_k(\tau) = 
-  \dot p_{u,\rm 01}(t) \delta q^{\downarrow}_0  - \sum_{i \neq 0 \in {\rm inj}} \int_0^t \dot p_{u,\rm i1}(t-\tau) dq^{\downarrow}_i(\tau) 






Again it is important to note a difference between

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