Implication that pressure  at any point  of a porous reservoir is a linear sum of pressure responses  to individual rate variations  in all wells connected to this reservoir:

p(t, {\bf r}) = p_i + \sum_k \delta p_k(t, {\bf r}) = p_i + \sum_k  \int_0^t p_{uk}(t-\tau, {\bf r}) \, dq_k(\tau)


In case reservoir point  defines location of -well the superposition principle can be rewritten as:

p_m(t) = p_{mi} + \sum_k \delta p_{mk}(t) = p_{mi} +  \sum_k \int_0^t p_{umk}(t-\tau) \, dq_k(\tau) = p_{mi} + \int_0^t p_{umm}(t-\tau) \, dq_m(\tau) + \sum_{k \neq m}  \int_0^t p_{umk}(t-\tau) \, dq_k(\tau)

where

specific component of -well pressure variation caused by -well flowrate history 

bottomhole pressure response in -well to unit-rate production in the same well (DTR)

bottomhole pressure in -well to unit-rate production in -well (CTR),