Before his employment with Shell, Dr. Willem Maarten van Haaften spend a decade at Tata Steel, where his work focused on carbon steels. It was only two years ago that he became involved with stainless steel, and as he said in a recent interview, “the field certainly presents a learning curve.”
But Willem Maarten quickly adapted to his new line of work, and at his current role in Shell’s Materials & Corrosion department in Amsterdam, Willem Maarten is focused on the longterm. “There are a lot of materials and corrosion specialists who are in working in plants around the world,” he explains. “These specialists are essential to help safely run Shell assets every day, tackling the daily issues and problems that may arise. My department in Amsterdam, however, is tasked with looking at issues over the long term. For example, we collaborate closely with suppliers to steer them towards providing the products we will need in four or five years. This ensures suppliers have the opportunity to develop the stainless steel products we need, on time, for the future. Another good example is our work to find new ways to develop fit-for-purpose materials testing.”
At the Stainless Steel World Conference 2019, Willem Maarten shared an example of the kind of fit-for-purpose research project he is involved with, in this case involving 13 chrome martensitic stainless steel. “We will use the new test method to qualify 13 chrome materials for conditions that are normally not suitable for this material,” he explains. “Our materials and corrosion team found that certain onshore wells in the Middle East constructed with 13Cr martensitic stainless steel have become increasingly sour over their lifetime, which means higher levels of H2S. If we were to requalify the material using test methods currently in the international standards at the conditions now present in the well, it would fail. And yet, we did not experience any failures in those fields. Faced with the choice of removing or reworking all the tubulars and replacing them with higher-grade materials, we needed to investigate this discrepancy.”
Carrying out fit-for-purpose testing and mimicking the conditions in the well confirmed that failures would not occur and demonstrated that the test specifications are overly conservative.
“In collaboration with Vallourec, Total and the National Physics Laboratory (UK), our team set out to find a better way to qualify materials; going forward, this could lead to significant cost savings. Of course, this type of research only works if you thoroughly understand the material and the environmental conditions in the field. If you can achieve that and mimic the conditions in tests, it’s a valid method for qualifying materials.”
This same research is highly relevant for older wells, where the reinjection of water to maintain pressure in the subsurface reservoir creates an environment that produces increasingly higher concentrations of H2 S. “While this example was an onshore gas field in the Middle East, it could potentially be a good solution for offshore wells. However, we would need to qualify the material for the set of conditions in each well.”
Shell has shared this research widely among other oil and gas majors and is keen to make this a generally applied method. According to Willem Maarten, “it will take several years to implement our findings as an ISO, or other, standard. Currently, we are working to expediate the acceptance of the fit for purpose testing method, which promises significant well completion costs. This work was partially presented at Eurocorr in 2019 with a lot of interest, and we are are happy to share our research. It’s a very conservative industry, so we know it will take time to spread the word and increase acceptance.”
New materials challenges
A common challenge with which the materials and corrosion experts must contend is achieving a combination of higher strength and corrosion resistance, especially for the wells requiring high strength tubulars and castings to minimise weight.
“For example, when we look at carbon steels, we’d ideally like to have a 140 KSI (965 MPa) material with sufficient sour resistance. The stronger the material gets, the more likely it is to have hydrogen embrittlement which presents a challenge for us. The main hurdle to switching to stainless steels in wells is the cost, so we try to do as much as we can in carbon steels. For most well applications there is probably a stainless steel grade which would function perfectly, but they remain too expensive, even considering the life cycle. It’s perhaps difficult to accept as we build our wells to last up to fifty years, yet in the end, stainless is still often considered too expensive.”