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One if the two Well Controls with Lift Mechanism trying to maintain the the actual flowrate

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body	q_L(t)

manually specified value of the flowrate.In physical

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body	q_{LL}

:

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anchor	LC
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q_L(t) = q_{LL} = \rm const

Liquid control is most common for producing wells with SRP and ESP.

The mechanical pump is trying to maintain the preset flowrate target flowrate

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body	q^{\uparrow}_{LL}

but it only succeed succeeds when the wellbore fluid level is abiove above pump location.

Once the If dynamic fluid level lowers all the way down to the pumping chamber, then the pump efficiency deteriorates and the flowwaret reduces while flowware reduces:

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anchor	P0I1Z
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while the fluid level and correpsonding corresponding BHP are getting stabilized.

except the case when bottomhole pressure is being reduced by the downhole pump to its minimal value, specified by the pump location inside the wellbore.

In case this happens the well is switching to Pressure Control until the formation pressure and allow pump produce efficiently above minimal bottomhole pressure value.

:

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

This value of BHP is called critical BHP

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body	p_c

and the fluid can not be lifted at the wellbore pressures below critical BHP.

This does not actually qualifies the well operation as Pressure Control and the well is still under Liquid Control conditions and once bottomhole pressure raises above critical value the pump returns to producing the target liquid rate

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body	q^{\uparrow}_L(t) = q^{\uparrow}_{LL} = \rm const

. Despite that many wells are operating under Pressure Control de facto they can be still simulated as under Liquid control assuming that their liquid rates have been manually pre-set adequately by Production technologist.

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