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control nipples, plugs, etc., seal assemblies, latches, and liner “Then the H S becomes an issue. Statistically all HPHT 2 hangers, Penman says. Some have already been published, wells will produce H S at some point in time. But that is not 2 others are close to being published and work is starting in other necessary always a problem. The issue is partial pressure H S. 2 areas to complete a suite of new standards. Meaning the: pH S = Total bottom hole pressure x fraction of 2

However, with more stringent standards, in most cases, the H S present. So, if a HPHT feld develops H S due to tempera- 2 2 result will be longer testing cycles, Penman warned. “Before, ture at a later point in the wells life, the bottom hole pressure typically between contract award and when had to put equip- has gone down and you might be OK (or not).

ment on the ground was about one year, and that was quite “Chloride is also an issue, mainly in relation to temperature. diffcult to do that. With this new API implications you are Chlorides in combination with high temperature affect alloys, looking at doubling that. There is a whole lot more involvement which is an issue for the production tubing, the tubing hanger going in to a HPHT situation.” and the casing hanger. And then what makes it really diffcult is

Despite the extra time it will add, Campfens sees the API the combination of H S and high pressure.

2 committee’s work as progress. ”For me, I see a huge step for- “The problem is, fnding materials with suffcient strengths ward. There were no standards, how to get equipment, before. suitable to accommodate all of these requirements can be dif-

We are moving on.” fcult as these can be in confict,” he says.

A material challenge Setting the grade

Materials selection for HPHT well construction is still a major Some issues can be overcome by moving to proprietary steel challenge, however. Henk Kramer, senior wells engineer, grades from specifc manufacturers for higher temperature uses,

Nederlandse Aardolie Maatschappij (NAM), in the Netherlands, which can handle some H S, if the pH is high enough. But, 2 outlined a minefeld of often conficting requirements for mate- defning the parameters in the drilling phase, when you are yet rials selection in HPHT at Offshore Energy. to defne the pH, is diffcult. In this case, a ‘worst case’ is often “In principle you want to make the production casing as light assumed, which is typically a value around pH 3.5.

and thin as possible. In that case, you do not need such a big Strengthening the pipe, without increasing the yield rig and the annular clearance is bigger so that the fow dynam- strength too much, usually results in increasing its thickness, ics are optimized. Also in terms of geometry you are restricted which then introduces manufacturing issues as it becomes by the size of the BOP at the top and the size of the perforation more diffcult to have homogenous properties through the guns you need inside the last liner at the bottom. metal during quenching, Kramer says. “So we are getting to “In HPHT wells you need higher resistance to pressure. But, a limit where it is increasingly diffcult to make metals with the right properties,” Kramer says. “We have come a long way in HPHT wells but we still make steel the same way.

We are getting to the edge of what we can do at current steel mills.”

Pipe connections also have to be as strong as the pipe.

Usually, seal face imperfections are sealed with an API modifed dope, which is a mixture of oil with zinc, lead, and copper elements in it. The lead particles especially help to smooth out the imperfections, but importantly, it is stable at high temperatures. But, rather than conficts in material specifcations or manufacturing capability, this time regulations, in the Netherlands, and it is expected in the UK, are set to phase out use of lead offshore due to environmental concerns and rightly so, Kramer says. There has been a lot of work done to create a green dope, replac- ing lead with Tefon fakes and other alternatives, but they are limited by temperature.

Gaining confdence in the connections also has to be built. Historically, every company had its own standards for testing connections, Kramer says. “Only in 2002, the industry came up with standard procedure for testing con- nections,” he says.

But since then, pressures and temperatures have increased and more confdence is needed in the connections.

Henk Kramer, senior wells engineer, Nederlandse Aardolie Maatschappij (NAM)

An ISO standard for CAL IV testing has become more prescriptive and is pushing the connections very close we cannot really change the OD too much because of the limits to the edge of what is possible, and for HPHT requirements of the BOP, fow dynamics and other physical limitations. sometimes over the limit, which is a concern and often results “Same for the wall thickness, if you increase it too much in custom designed connections for a particular HPHT well, the bit for the next hole section does not ft anymore. That

Kramer says. leaves the yield strength as the most obvious to increase if

Overall, “it’s getting more and more extreme what we need” the pressure rating needs to be higher.

to work in uHPHT environments, Kramer says. oedigital.com December 2015 | OE 29 028_OE1215_HPHT1_OffshoreEnergy.indd 29 11/21/15 12:32 PM