Well Integrity Technical Section

Impact of H2S on downhole completions is well explained in NACE MR 0175 however I could not find any article/guidelines or standard which specifically define the severity & impact of Mercury & Mercaptans on downhole completions.

Could anyone explain & share the case histories regarding impact of Mercury & Mercaptans. Is there any standard? 

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Lajpat Rai
Petroleum Engineer
United Energy Pakistan Ltd
Karachi City
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Mercury is not corrosive to conventional completion metallurgy.

Liquid Metal Embrittlement is not a concern for steels and Ni-Cr-Mo alloys used in completions.

Al, Cu and Ni-Cu alloys (see below) should not be used if exposed to mercury.

(Cu plating will be lost if exposed but Cu-plated threads are not excluded).

Recovered equipment may require decontamination.

There is little literature dealing with downhole exposures; notable exceptions are NACE Corrosion Conference 1990, paper numbers 57, 58 about the Arun Field in Indonesia. Several tubing metallurgies were tested for mercury exposure.

More generally, mercury causes problems for surface processing because of:

1. Accumulation and toxicity.

1. Liquid metal embrittlement (LME) of aluminium and copper alloys that are mainly used in cryogenic gas plants. Ni-Cu alloys as (eg) 'Monels', alloy 400 (UNS N04400) and alloy K-500 (UNS N05500) have also been shown to be susceptible to LME so require caution.

There is extensive literature dealing with these issues; the above is an overview only.

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Edward Wade
Metallurgical Engineer
MetalEcosse Ltd.
Fife

Mercaptans

Mercaptans are potentially troublesome in refineries as contributors to 'high-temperature' sulfidic (or sulphur) corrosion. However they are not normally considered for downhole metallurgy selection.

 I am not aware of any downhole corrosion concern associated with mercaptans or any guidance requiring their consideration so believe they can be ignored.

This is consistent with a wider assessment by C P Dillon in NACE Materials Performance (December 2003, p57), that stated: "The lower molecular-weight-compounds, .....such as those encountered in petroleum production and used to odorize natural gas, should be expected to cause sulfide-related attack − sulfide stress cracking or hydrogen-affected cracking in susceptible steels in the presence of water − but this has not been observed in practical applications .......".

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Edward Wade
Metallurgical Engineer
MetalEcosse Ltd.
Fife