Oil company investigators have yet to announce conclusions about what went wrong at Kashagan in October, when onshore pipes carrying corrosive gases sprang leaks and brought offshore production in the Caspian Sea to a halt a month after start-up.
It has now emerged that sulphur-laden sour gas burped out from the oil field during production last year may have weakened long stretches of processing pipelines, two sources said.
"The problem goes on for kilometre after kilometre, it's a systemic problem," an industry source briefed by Kashagan engineers told Reuters.
That defective stretch of pipeline runs mainly through hard-to-reach swampy terrain, making intervention costly and difficult.
The consortium said only that toxic gas lay behind the problem. "Sulphur stress cracking was identified as the root cause of the pipeline issues," the spokesman said. "This process occurs if steel of high hardness is exposed to high concentrations of H2S (hydrogen sulphide) under high pressure in the presence of water," the spokesman said.
"This mechanism is not at all related to normal corrosion (formation of rust) but solely to the hardness of the steel".
The reservoir fluid is a 43 °API light oil, with a GOR of about 2,850 scf/stb, mostly stored in the first medium. Notably, high sour gas content (16% H2S, 4% CO2) imply relevant HSE challenges for field management.
The Kashagan field is a deep, over pressured (initial reservoir pressure: 783 bar), isolated, carbonate build-up with a high-permeability, karstified and fractured rim and relatively low- permeability, stratified, platform interior. The field contains a 43-degree API light oil, with 15% H2S and 5% CO2, and contains more than 100 Tcf of associated gas.
One of the biggest challenges of the Kashagan field development is the management of huge volumes of highly sour associated gas. The consortium had essentially two options to address this challenge:
• A commercially unattractive, but technically not challenging, conventional choice of evacuating the sour gas to shore for treatment (H2S and CO2 removal) and sales; or
• A technically very challenging, but potentially economically beneficial, alternative of injecting the raw sour gas back into the reservoir.
This injection alternative, with its high discharge pressures and sour service, would extend the current capabilities of existing gas compression technologies. Nonetheless, it had the potential to significantly enhance oil recovery, as the Kashagan oil and injected gas are first contact miscible at pressures well below the initial reservoir pressure.
The initial reservoir pressure (Р res init) exceeds the saturation pressure (Рs) by 50 МPа which ensures long-lasting stable production of the field
Airplane manufactures use ultra low sulfur alloys explicitly because sulfur increases the brittleness of steels. Steel's absorption of sulfur in high hydrogen, carbon dioxide environments is a well known phenomena. It would be expected that in an environment, such as Kazakhstan presents, that this would be closely monitored. Sulfur content is usually measured through high frequency infrared absorption. This was obviously a failure on the part of the project's engineering staff. It is not, however, the primary reason why the project after seven years is $20 billion over budget, and almost 1 mb/d behind schedule!
the local temperature variance is huge , it goes from 40Dg C to minus 30 easily
could it be an issue , I don't know , just a guess
They know the proper specs for metal used in the space shuttle, submarines, North Slope production equipment and nuclear plants. They knew exactly what specs were required at Kashagan. And they didn't use the proper material. Why? I don't know. But the requirements would be well understood by any competent engineer.
The $50bn Kashagan oil project in Kazakhstan is likely to be delayed by two more years while 200km of pipeline is replaced, in a further blow for the companies developing the largest oilfield outside the Middle East.
Erbolat Dossayev, Kazakhstan’s minister for economy and budget planning, told the FT that he expected production to start at the end of next year at the earliest – but that it could be delayed until 2016.
rockdoc123 wrote:My experience is the tendency these days in big projects is to not over engineer facilities (i.e. zero risk of failure) but get to that point where it is still low risk but more cost beneficial. In the good old days it was more common to engineer to avoid any chance whatsoever of failure. Unfortunately this made many projects uneconomic and the industry gradually seemed to move to accepting a bit more risk (with the exception of potential high impacts).
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