It is possible that we'll head pressure will change. It usually reduces with production volume removed, but it can also increase. Even if bottom hole pressure remains constant, a lighter column of fluid in the production string, due to oil displacing water, or gas displacing either oil or water in the present production stream, means that there is less pressure to be subtracted from that same downhole pressure, resulting in higher surface pressures probably during both production and during shutin. If the future stream is predicted to contain more of either oil or gas than the present stream has, it is possible to register higher surface production and shutin pressures. It is also possible that downhole pressure increases or decreases later on, perhaps due to water, or oil entering or leaving the formation, thereby changing the hydrostatic head making up the downhole pressure.
During production, there are additional flow losses to consider, so depending on flow rate, string diameter(s) and flowing Pressure drop, surface pressure could go either way. That will be highly dependent on Reservoir fluid contents, rock characteristics, string design and the expected optimum reduction rate. Your reservoir engineer probably knows best what to expect. He has all the information, so believe him, at least until proven wrong.
Of course if injection will be used, well pressures will probably increase everywhere.
At least it is usually easier to design for higher pressures later than it is to design for lower pressures later on.
Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."
