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The absolute value is staying between
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For complex well designs with varying pipe flow diameters and water source/stocks which may lead to substantial variation of flowrate the wellbore model can be split in segments each having a constant friction factor.
For the horizontal sections of wells and surface pipelines the value of friction-based pressure loss dominates over vanishing gravity-based pressure build up and requires more accurate calculations of Darcy friction factor with account of its variation along the flow.
Derivation
Consider a ration between friction-based pressure gradient
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In case of slanted wells even a strong the inclination will not change the friction contribution by much (may increase by from 3 % up to 5 %).
For the horizontal sections of wells and surface pipelines the value of friction-based pressure loss dominates over vanishing gravity-based pressure build up which zooms the value of accurate calculation of Darcy friction factor with account of its variation along the flow. In the meantime, for strongly inclined/horizontalised pipelines the pressure/temperature variation along the pipe is very minor, so is the water viscosity, and Darcy friction factor agains has very little variation.
See also
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Physics / Fluid Dynamics / Pipe Flow Dynamics / Darcy–Weisbach equation / Darcy friction factor
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