@wikipedia

Stationary flow with reservoir and fluid staying at quasistatic equilibrium and fluid pressure and temperature are not changing in time:

p(t, {\bf r}) = p({\bf r})

T(t, {\bf r}) = T({\bf r})

Well production or injection resulting in steady state flow is characterised by:

q(t) = q = \rm const

p_e(t) = p_e = \rm const

p_{wf}(t) = p_{wf} = \rm const

J(t) = J = \rm const