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-\tau, {\bf r}) \, dq(\tau) |