Modifying the Fluid Flow Equation System

Hi everybody,

Is it possible to change the fluid flow equation system in order to fit a logarithmic function in the derivative? I am currently using the earth science module to model a dual porosity fluid flow system. However, my numerical model requires me to have the derivative of a logarithmic function of pressure as opposed to just a pressure time dertivative. In other words I have

d(ln(p))/dt instead of d(p)/dt

where p is pressure and t is time. As far as I know, it is possible to change all terms of the equation system except for the derivative term. Any advice?

Thanks and Best Regards,

Andres Bracho.