Fluid injection test, long time

The conditions required to measure the three-dimensional storage coefficient R in the long-time limit are that $\delta p_f^{(1)} = \delta p_f^{(2)}= \delta p_f$, while $\delta p_c = 0$.It follows therefore from (defs) and (storage) that  

$$R \equiv \left. {{\partial \zeta}\over{\partial p_f}}\right ... ...}} + \phi\left({{1}\over{K_f}} - {{1}\over{K_{\phi}}}\right).$$ (22)