Subsurface reservoir with properties staying constant across the reservoir volume:
M({\bf r})=M =\rm const | \phi({\bf r})=\phi =\rm const | c_t({\bf r})=c_t =\rm const |
h(x)=h =\rm const |
There are no homogeneuous reservoirs son real life but the concept plays important academic role and also has a good number of practical applications to characterize the distributed field properties with some average value.