Equation, expressing that total pressure p(t, {\bf r}) in any point of a reservoir {\bf r} is a sum of pressure responses \delta p_k(t, {\bf r}) to individual rate variations q_k(t) all offset wells k:
| 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) |
Applies to single-layer linear diffusion model