Older wells can raise production with EOR

by ArabianBusiness.com staff writer on Thursday, 01 March 2007

A multiphase meter installed on a nine-well platform.

The World Energy Organisation estimates that more than 70% of the world's oil and gas production comes from fields that are more than 30 years old.

In the Middle East many fields have been producing oil for even longer and although they have prolific capacity, getting the most out of a reservoir is still important. Various predictions exist for how global hydrocarbon consumption will grow over the next 50 years. No matter what number is believed, it is clear more oil will be required, making it important to increase recovery rates from existing or ‘brownfield' sites. This need is driving increasing industry interest in enhanced oil recovery (EOR) and the optimisation of existing fields.

The scale of the issue was described by John Barry, vice president of unconventionals and EOR for Shell, in a recent online seminar.

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"The world has less and less of what I like to call the ‘easy oil' left," said Barry. "On average across the industry, from reservoirs around the world, recovery is perhaps only 35% of the oil that was actually in the reservoir to start with. This is after we've done the primary recovery phase ... and even the secondary recovery phase. Really that's not very much. That means two-thirds of the oil, typically, is left in the ground. The purpose of EOR is to try to get that recovery percentage up.

"It doesn't really generate new oil fields, but it helps us get more out of existing oil fields. It's potentially quite significant to society because supposing we could increase recoveries by 10% towards 45% on average, we are talking about a number, which is probably a bit controversial, but something like 500 billion barrels, depending on which database you refer to. At today's production rates that would mean about 20 years extra production for the world, so it's a pretty significant technology if we can get it going in a more widespread way."

Different techniques and tools exist to aid EOR. Some have extensive proven performance records in the field. Others are emerging and the conservative oil industry is slow to adopt anything without a substantial amount of success behind it. But with oil fields across the region only getting older, the need for the expertise is growing.

"The major part of our work is related to optimisation of fields," said Nabil Alalawi, managing director of Almansoori, an oil field services company. "The older the fields are, the more they need the kind of services we offer; just as a person needs a doctor more when they're sixty than when they're twenty. Since many fields in the GCC have been in operation since the early fifties, there is a growing amount of work for us."

While people see the scope of this kind of work in the region growing, they acknowledge there is much to learn and that the willingness to experiment will depend on the potential value of the returns.

"Currently the industry is still trying to fully understand the EOR opportunities in the Middle East," said Graeme Jack, consultancy director for Petrofac Engineering and Construction. "Size means that there are some tremendous EOR opportunities, however the exploitation of the additional reserves will require large amounts of capital and, possibly, the use of some innovative EOR techniques. It is a growing area of interest in the Middle East and in particular to Petrofac.

"The key to successful EOR development in brownfield environments is to maximise the use of existing facilities while recognising that the operation of these facilities may change quite significantly," said Jack.

These operational changes are derived from the mix of old and new technologies in place on older drilling rigs. These have frequently had a series of upgrades installed over a long period of time. Many brownfield sites still use the technology they were originally equipped with decades ago, when the fields were in full production. Such technologies are often outdated and unable to maximise the reservoir's performance.

Until recently exploration and production operators have been unwilling to make the investments needed to improve recovery. In these times of strong oil prices, new technologies are being greeted with more enthusiasm. The capital outlay can be justified with a rapid return on investment. Using unplanned shutdowns to install modifications is one way of maximising the opportunity for improvement, while minimising disruption to production rates.

Various EOR techniques are in circulation and their application depends on the characteristics of the reservoir in question. Common techniques in use include chemical flooding, using alkalines or micellar-polymers; thermal recovery, such as steam flooding; and water reinjection. One other that has captured a few headlines thanks to its perceived environmental benefits is the use of CO₂ sequestration.

"CO₂ sequestration serves a dual purpose, increasing oil recovery and reducing CO₂ emissions," said Jack. "We are particularly interested in CO₂ sequestration and steam flood. While these bring significant engineering and logistical challenges with them, they hold great promise for the future."

Oman sees much of the most technical EOR work in the Middle East region, due to the more challenging nature of its reserves. Petroleum Development Oman (PDO) recently announced the award of contracts related to its Marmul Polymer Flooding project, its latest multi-million dollar enhanced oil recovery (EOR) project.

The contract was awarded to a consortium led by France's SNF with the UK's Mott MacDonald as design contractor and Oman's Bahwan Engineering Company as construction contractor. The contract involves building centralised water treatment and polymer preparation and injection facilities as well as the supply of chemicals for five years.

Oman's Marmul field was discovered in 1956 and its main Al Khlata reservoir has very heavy, viscous crude. It is expected that production will be increased by a substantial 10% through the use of the polymer flooding. The technique works by adding polymer to water in order to make it more viscous, before it is injected into the reservoir. This leads to more effective oil recovery through increased pressure.

Joseph Stephen, general manager of Special Oilfield Services in Oman, a joint venture with Almansoori, says that although new technologies are emerging, steam and polymer flooding are still the main options in the country.

"Steam flooding especially is a big driver of the EOR industry in Oman," said Stephen. "The crude here is quite heavy and while there are other techniques to reduce viscosity, they are not mature; their rates of success have to be carefully studied."

However, while enhanced recovery techniques take the headlines, there are a number of other ways to enhance recovery from brownfield sites. For instance, well testing can help determine the optimal production capacity of each well over the lifetime of the field. This can avoid the risk of overproduction, while accelerating production and increasing recovery rates. The problem can be the time taken to do this on older sites, which may not have the appropriate infrastructure in place. Time equals lost production, which in turn means lost revenue.

One technique to increase the number of well tests and reduce the amount of oil lost, without the need for an expensive infrastructure overhaul, is the installation multiphase meters on wellhead platforms. These can be used to determine oil, water and gas flow and provide additional characteristics like slugging tendency, watercuts, gas void fraction and gas-oil-ratio. This information can then be used to improve well performance, without the production losses sometimes associated with testing.

With water reinjection also being a technique used in EOR, there is a demand for cleaning and filtration services to improve the quality of the water.

Pranav Kapoor, manager for the filtration and fluid treatment division of Hydrolink, explained that clean water, without the presence of silt and sand, is an essential part of the reinjection process.

"The water that comes out of the well has to be treated before it is reinjected," he said. "If it's not clean, it can harm the quality of the well, with silt blocking pores within the well structure."

Techniques to purify the water include hydrocloning, where centrifugal technology is used to separate particles and oil from the water. Further ‘polishing' techniques can reduce the particle content even further. Kapoor sees the Middle East demand for these kinds of services growing.

"Many installations are old and their equipment obsolete. As wells get older and pressure depletes, reinjection to aid recovery becomes more necessary," he said.

With this recovery technique comes the need to monitor oil in the water. Recent changes include the commercial launch of an oil-in-water monitor developed in a joint industry project between Roxar, TNO Science and Industry, Statoil, Eni SpA, Italy's second largest trading company, Shell and PDO.

Oman's involvement indicates the importance of these kind of techniques to its fields. EOR techniques, such as water reinjection, will continue to become more prevalent and continue to need the support of related services.

Case study

Examples of multiphase meter technology in action include Roxar installations on offshore platforms in the Middle East. The field in question is a mature field offshore, discovered in the early 1960’s, with significant oil reserves. The field peaked at 50,000 bpd in the early 1970’s but declined to 20,000 bpd by the 1990’s. Previously one centrally located test separator served the brownfield with the platforms unmanned and having limited power.

Not all platforms had test lines. Some had to be shut in to be tested and there were long distances between the wellhead and test separators. These factors contributed to inevitable production and accuracy costs with only half of the producing wells being tested each month and oil being regularly lost, due to the shut in of wells while other wells are being tested.

The Roxar multiphase meters were installed on wellhead platforms – each of which had between one and nine wells. The quarterly average number of well tests taken per month since the multiphase meters have been installed, has increased from an average of 50 to 120. The amount of lost oil due to well testing has also been greatly reduced from a typical figure of lost oil per month of 12,000 barrels to between 20 and 50 per month.

Over the last few years, through the implementation of new technologies and drilling systems, the operator has successfully reversed nearly 25 years of steadily declining production. Now, the field is producing 138,000 barrels per day – almost three times the previous peak.

“The key to successful EOR development in brownfield environments is to maximise the use of existing facilities, while recognising that the operation of these facilities may change quite significantly.” - Graeme Jack

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