Tim Miller discusses TCO’s changing approach to maintaining its mission-critical process vessels with the use of innovative technology
Kazakhstan, officially the Republic of Kazakhstan, is the world’s largest landlocked country, and the ninth largest country in the world, with an area of 1,052,100 square miles. Between its most distant points, Kazakhstan measures about 1,820 miles east to west and 960 miles north to south. It is a transcontinental country largely located in Asia, but with the most western parts in Europe. Kazakhstan is the dominant nation of Central Asia economically, generating 60% of the region’s GDP, primarily through its oil and gas industry. It also has vast mineral resources.
Lowlands make up one-third of Kazakhstan’s huge expanse, hilly plateaus and plains account for nearly half, and low mountainous regions about one-fifth. The western and southwestern parts of the republic are dominated by the low-lying Caspian Depression, which at its lowest point lies some 95ft below sea level. The ancient Caspian Sea bottom is where the Tengiz oil field was discovered in 1979.
Tengiz Oil Field
The Tengiz reservoir, holding 26 billion barrels of oil and gas is very large, very deep and has a high sour gas (hydrogen sulphide or H2S) content of about 6%. It is a complex and difficult operation. The operator of the Tengiz field is Tengizchevroil LLP (TCO), which is a joint venture between Chevron (50% share), ExxonMobil (25% share), KazMunayGas (20% share) and LukArco (5% share).
The joint venture was formed in April 1993, when the Kazakhstan government granted an exclusive 40-year right to TCO to develop the Tengiz and Korolev oil fields located in the north-eastern reaches of the Caspian Sea in Kazakhstan. TCO is a very prolific producer in Kazakhstan. The company generates roughly 30% of the country’s total production with crude production of about 540,000 barrels a day from approximately 100 wells. The crude production per well is very high and includes a significant amount of natural gas and natural gas liquids.
A mix of oil trains
Six separate trains currently process the sour crude into marketable components of sweet crude oil, sweet natural gas, natural gas liquids and sulphur. Four of the trains are an old Soviet design called the Komplex Technical Lines or KTLs. A fifth KTL train of similar design was put online in 1997 and finally the newest second generation plant (SGP) accounting for half of current total production was put online in 2008.
TCO is executing a mega-capital project right now, the Future Growth Project and Wellhead Pressure Management project. This is a US$36.8 million project that has grown in cost over the past couple of years to about US$45 billion. It is a massive project that will add the seventh train of production to TCO. This project is in construction now and should be online in about 2023. The scope and scale of the operations at Tengizchevroil is unmatched in the region. It is one of the busiest places in the world and one of the most interesting and challenging oil fields you will ever see.
Shutdowns and turnarounds for Tengizchevroil LLP
The SGP suffered from early reliability and design problems and as a result, a number of full-plant maintenance shutdowns were taken during the first years of operation. Some of the process vessels in SGP were internally coated with organic compounds and these coatings did not prove to be robust given the high temperature steam outs and flushing required during maintenance shutdowns.
Coating repairs, patches and replacements seemed to be never-ending. Therefore, TCO reliability and metallurgical experts began working on alternatives to consider that would protect the base metal in the aggressive environment found in the process vessels and withstand the flushing and cleaning processes required during shutdowns.
With six trains in operation and the seventh train to be added, the annual maintenance and turnaround programmes are very important to TCO’s success. Each year, one to two trains are taken down each year in the summer, representing 25-50% of TCO’s daily production of 540,000 barrels.
The full turnaround programme each year usually lasts between 30 to 40 days in duration. With 135,000 to 270,000 barrels per day off for 40 days, you can imagine the cost of just a few hours delay in the maintenance programme. Therefore, TCO has four main priorities for annual turnarounds. Safe execution is the first priority. TCO will often bring in 6,000 additional workers to complete the turnaround scope annually. Their safe mobilisation, health and safety on site and demobilisation is the priority.
Reliable execution of the maintenance scope is the second priority. On-time and on-budget work is essential to the definition of success. Getting the production back online even hours earlier than planned can bring huge rewards.
The third priority is long-term integrity of the maintenance work. Each single process vessel will be expected to operate for four to five years before it is inspected again and opened for maintenance. Failure to operate reliably for the operating period (four to five years) becomes a costly and unexpected repair for TCO.
The final priority is costs. The execution of the annual programme is budgeted each year and accounts for about 10% of the operating and capital budget. Although costs always matter, they are not more important than safety, reliability and integrity. Therefore, TCO prioritises the repair and corrosion protection process that will more likely meet the first three priorities of a turnaround over the installation/application costs. That is why companies such as IGS (Integrated Global Services) are critical to TCO’s success in the turnarounds. TCO needs companies with a proven record of success to come in, do their work safely, reliably and on-time and using a proven technology that consistently shows integrity – i.e. it will last five years or more.
A Tengizchevroil LLP crude oil desalter case
One proof point to use as an example is the crude oil sesalter vessel in the GP, which is the sixth train at TCO and represents about 50% of its production. This is part of a system that was put in place in 2004 and put online in 2008.
The process conditions of the crude desalter include hydrochloric acid that is generated by the hydrolysis of the salts that are naturally occurring in the Tengiz crude. The system may also have some sour gas or H2S, which could lead to corrosion and cracking of the vessel shell. The desalter was built with an organic lining in place upon installation. However, this organic lining proved to be inadequate protection from the process environment and was found to be lacking the toughness to withstand the aggressive nature of the steam-out pressures and steam-out temperatures during maintenance events. TCO would repair the organic coatings, put the internals back in the system, but was seeing failures every time the system was taken up and down.
The key in corrosion mitigation is being able to put something in place in the field that’s going to be robust. Often, companies will recommend a technology or system that works fine in the laboratory, but the question is “can you install that lining/coating in the field and will it last for five or more years?” Another consideration in the field application is how forgiving it is when entering and exiting the vessel and while reinstalling the internals. One of the biggest fears in an operation such as the SGP is the loss of integrity. It is critical that all of the process fluids (oil, sour gas, water) that are in the system, stay in the piping and the process vessels. Any loss of integrity is a major problem where people are working nearby.
A novel and highly resistant coating/lining system was needed as a barrier to keep the aqueous H2S from contacting the base material and that will withstand the steam-out pressures and temperatures. That is when TCO started working collaboratively with IGS more than a year before the first major turnaround was scheduled for SGP.
Turning point for Tengizchevroil LLP
In 2012, during the first big turnaround for SGP, the organic lining in the crude oil desalter was replaced with an IGS high-velocity thermal spray metal coating that had been specifically designed for the conditions seen in the vessel. IGS came in, did the planned work and completed the full scope ahead of time. The final inspection of the thickness and integrity of the lining was completed before closing the vessel and it passed all inspections with a very uniform coating having been applied.
Four years later, during another turnaround at SGP, the coating was intact with no apparent thickness loss. 2012 was truly a turning point in the life of the SGP crude oil desalter vessel. TCO’s 2021 turnaround of SGP is less than a year away. Once again, TCO will have a chance to inspect this vessel again and may indeed pass another four-year cycle with the coating securely in place and functioning as designed.
The questions to ask
As you think about the value proposition of coating and liner installations during a turnaround, you have to ask yourself a number of questions. Firstly, is the coating system going to be robust in the field? It may do well in the lab, but can it be installed in the field with integrity and will it remain intact as you replace the internals and you walk around inside of the vessel? Secondly, is it going to last until your next turnaround and for even longer? Operations such as SGP can ill afford a loss of integrity and unexpected downtime outside of the planned maintenance cycle. Lastly, what is the cost of application? Although the thermal metal spray coating may be more expensive than organic coatings initially, the overall full-value cost need to be taken into consideration. In the 2012 turnaround, IGS shaved three days off the critical path during installation, saving millions of dollars in the process and allowing the process trains to be started up early. Now the desalter vessel is passing the eight-year mark since the spray-metal coating was installed – and it is still going strong.
Tim Miller is executive director - Reploublic of Kazakhstan and global upstream operations advisor at IGS