Hey Guys
Has anyone ever had experience with or modelled a downhole choke for a gas well to manage tophole pressure and reduce temperature drop across wellstream choke?
I'm looking at a typical gas well and hydrates / wax downstream of the wellhead choke. The flowing tubing head pressure (FTHP) from the well could range from 90 - 160 barg at flowing tophole temp approx. 35C and the pressure is let down across the choke to 75 barg.
At an FTHP higher than 100 barg methanol & PPD requirements are excessive.
Apparently when the pressure is reduced downhole the gas stream will heat up because of the high ground temperature. This results in a lower flowing tubing head pressure (FTHP) and a higher temperature downstream of the wellhead choke valve.
So the plan is to install a downhole choke to limit the FTHP to 100 barg at FTHPs higher than this.
I have simulated this in HYSYS using pipe segments and varying ground temperature with depth. The result is that at very low flowrates the temperature could be 4-6degC higher. However at the design flow the temperature is only 0.1-0.5 degC higher. This is because decreasing the pressure downhole increases pressure drop in the tubing and so temperature drop of the process fluid is more (which pretty much cancels out heat gained from the downhole pressure drop).
The temperature drop at a pressure drop downhole is less as the wellbore is in the dense phase region (300-400 barg)
The purpose for this exercise is as an alternative to a wellstream heater. From what I have simulated I think a heater is the way to go unless someone has some proof this downhole choke can work.
Appreciate any help
Thanks