Well Integrity Technical Section

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  • 1.  CO2 corrosion

    Posted 07-11-2015 04:31 AM

    Hi ,

    Gas injection is being carried in older wells ~ 10-20 years age. Casing integrity is good so far. We are trying to increase CO2 % from 3% to ~6% in gas injection. Will increase in %CO2 cause corrosion in casing. There is no water. Injected gas is dry.



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    Lajpat Rai
    Petroleum Engineer
    United Energy Pakistan Ltd
    Karachi City
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  • 2.  RE: CO2 corrosion

    Posted 07-12-2015 10:51 AM

    Hi Lajpat,

    CO2 is not corrosive if there is no water. The maximum amount of water allowed is debated, but the order of magnitude is around 500 ppm. That's not a lot, so you need to ensure that the gas is really dry. If it's dry, then there is no corrosion risk.

    If you're already injecting gas, CO2 should have a marginal effect on injection temperature and pressure (and viscosity), so you shouldn't see induced integrity failures - i.e. microannuli.

    A word of caution: once you add CO2 to water, you get the (arguably) most corrosive mixture in O&G. You should watch out for reservoir brine flow-back or production at other wells. Although if you're putting CO2 in the gas, chances are you're producing it already.

    Best regards,

    Matteo


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    Matteo Loizzo
    Well integrity consultant
    Berlin
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  • 3.  RE: CO2 corrosion

    Posted 07-12-2015 11:05 AM

    Lajpat,

     

    From the limited information supplied, no corrosion consequence is expected from the increased CO2 in the gas-lift annulus.

     

    No liquid water = no corrosion (downhole).  This applies above the active gas-lift valve.

    Normally, there is 'water' in the sump of a gas-lift annulus.  If present and static, it should not cause significant metal-loss corrosion of the casing for 3~6 mol% CO2 in the gas.

    (When there is an interface between 'sump water' and lift-gas, metal-loss corrosion of casing (that might be expected) is not normally troublesome).

     

    Minor deterioration, by corrosion or otherwise, may degrade 'old' casing so future integrity cannot be assured.

     

    Ed Wade.

    MetalEcosse Ltd,

    St Andrews, UK.

    UK Company number: 164518 (Scotland), registered address as above.  VAT registration number GB 671 0183 57.

     

     



    ------Original Message------

    Hi ,

    Gas injection is being carried in older wells ~ 10-20 years age. Casing integrity is good so far. We are trying to increase CO2 % from 3% to ~6% in gas injection. Will increase in %CO2 cause corrosion in casing. There is no water. Injected gas is dry.



    ------------------------------
    Lajpat Rai
    Petroleum Engineer
    United Energy Pakistan Ltd
    Karachi City
    ------------------------------



  • 4.  RE: CO2 corrosion

    Posted 07-12-2015 04:19 PM

    Hi Lajpat,

    As pointed out by another member, CO2 is not supposed to be corrosive in absence of water.

    However, I will like to highlight some points and will also like to see more information for proper prognosis. The following is based on the limited information provided by you.

    1. You have mentioned that injected gas is dry. What is the process used for dehydrating gas? For a normal operation, dehydration of gas is carried out to prevent hydrate formation or water condensation in the system. Complete removal of water is only carried out where it interferes with the process e.g. LNG production. My guess is that you may be using MEG/TEG for dehydration. Ensure that the system temperature doesn't fall below the water dew point of the gas, even when gas is not being injected into the well.
    2. You have mentioned gas injection. I assume that you are not planning to flow back the gas from the well, even in emergencies (often carried out in extreme cases like black start). If you have plans to flow back the gas, the gas will be saturated with water and may contribute to corrosion.
    3. Your query also mentions 'trying to increase CO2 % from 3% to ~6%'. What is the exact reason of the increase - is it a matter of choice or a change of the fluid characteristics/composition?

    I will also suggest that you to pull out all relevant data and discuss it in detail with the right disciplines in your company - Process and Corrosion. 

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    Sudeep Roy
    Geneve
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