Equation, expressing that total pressure in any point of a reservoir is a sum of pressure responses to individual pressure responses from all offset wells:
| p(t, {\bf r}) = p_i + \sum_k \delta p_k(t, {\bf r}) = p_i + \sum_k \int_0^t p_{uk}(t, {\bf r}) (t-\tau) \delta \, q(\tau) |