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The drainage volume difference

LaTeX Math Inline
body\delta V_{\phi} = V_{\phi, 2} - V_{\phi, 1} >0
 may be related to the fact that water injection W2 is shared between
LaTeX Math Inline
bodyV_{\phi, 1}
 and another reservoir  or with another producer. 

Case #1 –  Constant flowrate

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production: 
LaTeX Math Inline
bodyq_1 = \rm const >0


The pressure response 

LaTeX Math Inline
body\delta p_1
in producer W1 to the flowrate variation 
LaTeX Math Inline
body\delta q_2
 in injector W2:

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Expand
titleDerivation

Consider a pressure convolution equation for the BHP in producer Wwith constant flowrate production at producer W1 

LaTeX Math Inline
bodyq_1 = \rm const
 and varying injection rate at injector W2 
LaTeX Math Inline
bodyq_2(t)
:

LaTeX Math Block
anchorCase2_PSS_p11
alignmentleft
p_1(t) = p_i - \int_0^t p_{u,\rm 11}(t-\tau) dq_1(\tau) - \int_0^t p_{u,\rm 21}(t-\tau) dq_2(\tau) = p_i - \int_0^t p_{u,\rm 21}(t-\tau) dq_2(\tau)

Consider a step-change in injector's W2 flowrate 

LaTeX Math Inline
body \delta q_2
 at zero time 
LaTeX Math Inline
body\tau = 0
, which can be written as: 
LaTeX Math Inline
bodydq_2(\tau) = \delta q_2 \cdot \delta(\tau) \, d\tau
.

The responding pressure variation 

LaTeX Math Inline
body\delta p_1
in producer Wwill be:

LaTeX Math Block
anchorCase2_PSS_p11
alignmentleft
\delta p_1(t) = p_1(t)-p_i = - \int_0^t p_{u,\rm 21}(t-\tau)  \delta q_2 \cdot \delta(\tau) \,  d\tau = - p_{u,\rm 21}(t) \cdot  \delta q_2



Case #2 – Constant BHP: 
LaTeX Math Inline
bodyp_1 = \rm const


The flowrate response 

LaTeX Math Inline
body\delta q_1
in producer W1 to the flowrate variation 
LaTeX Math Inline
body\delta q_2
 in injector W2:

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