2 replies to this topic

[Michael_W]

Dear All, 

 

I have read various documents on oil and gas well production start-up (black start, after long shutdown) and each document I looked at seem to suggest different methodology in start-up. 

 

We normally have to equalize pressure on the SCSSV, which can be a self-equalize type or we can equalize using diesel or high pressure gas to equalize the pressure on either side of the SCSSV. However, I have never read any document which mentioned about equalizing the pressure for SSV, wing valve, choke valve and production diverter valve. 

 

Is there anyone who can enlighten me on this?

 

Thanks in advance. 

 

 

[paulhorth]

Michael,

 

Since no-one else has responded to your query I will try to address it but I do not have a complete answer. I am not a well operations engineer, but I have read procedures, like you mention, but I cannot unfortunately remember the details.

Some wellheads have facilities for injection of MEG or methanol into the top of the tree beween the upper master valve and the wing valve. The purpose can be to avoid hydrates when the well is started, but this connection could also be used to pressurise above the upper master and balance across it. I don't know if this is necessary though. Another possibility is when you pump into the wellhead to pressure balance the SCSSV, you open the upper master valve and so the balancing pressure exists through the well and tree up to the wing valve. Then close the upper master again before opening the SCSSV. The well fluids are then held by the upper master  valve, as they should be, until production is started.

The choke valve is usually mounted flange to flange with the wing valve (I think?) so there is no need to balance across the wing valve between the wing and the choke. The choke valve is designed to take a pressure drop so it can be opened against the full upstream pressure without balancing. The production routing valve, downstream of the choke, would be opened before opening the choke. so both sides of it are not pressurised.

 

However I do not have the right background to be confident that my description is the right way, and I am ready to be put right by others on any of these points.

 

Paul

[Michael_W]

Paul,

 

Thanks a lot for your reply and for keeping the discussion going. 

 

Yes, I do agree with you on the use of MEG or methanol to prevent hydrate formation and to equalize the SCSSV when its self-equalization (assuming it is a self-equalizing type) does not work as intended to.

 

I have read about your suggested method of start-up. I am wondering if the choke valve can be opened without equalizing as the amount of torque could be pretty high. If there is enough torque to open the valve, will it damage the valve seating and etc especially if there is presence of sand? Perhaps, the torque issue is taken care by pressure-balanced flow trim in some of the websites of choke valve suppliers and erosion taken care by proper material selection. 

 

Another method I have read is to keep the valves (SSV, Wing, Choke) opened all the way till the production header isolation valve. Other methods which I am not too convinced are methods such as opening SCSSV and subsequently opening lower master, followed by SSV, wing valve, choke valve without any equalization; the reason is that the actuators are designed to handle the pressure differential at all these valves. 

 

Anyone else has other ideas?

 

 

Regards,

Michael