SIEMENS

It’s a well-known fact that crude oil can’t be pumped out of the ground until a well goes dry. The amount of oil that can be extracted from a well depends on the nature of the deposit and the properties of the oil that lies within it. The average recovery factor worldwide today is between 35 and 40% of a total deposit. And only around 10 % of the petroleum is initially channeled by natural pressure into boreholes, which can extend to depths of between 3 and 6 km. From there it is pumped to the surface for further processing.
Once the natural pressure in a deposit begins to abate, oil companies need to get creative. One method they use is to pump water or gas into the ground in order to increase reservoir pressure. The artificial pressure displaces the oil and forces it into the borehole. Use of this technique often raises the rate of extraction by 20%, or by 30% at most.
Another option is to pump in steam. This increases reservoir pressure and lowers the oil’s viscosity, which allows it to flow more easily into the borehole. Despite their varying degrees of effectiveness, these methods have the same drawback: They require sophisticated technology that is also very costly in relation to the amount of oil it frees up for pumping.
That’s why it used to be a very common practice to close a well when it showed signs of exhaustion, and then to move on to a new oil field. Today, however, a growing number of oil drilling companies are taking another look at extracting more crude from older deposits — not least because of the anticipated high price for crude oil over the long term.
A recent study conducted by the U.S. Department of Energy found that "mature" deposits in the West contain up to 200 billion barrels of oil (1 barrel = 159 l), and that at least 89 billion barrels of this oil could be extracted in subsequent operations using the methods described above. This figure can also be expected to increase as extraction techniques improve.
One man who is working on refining such extraction techniques is Russian physicist Dr. Andrey Bartenev, the director of the Power Engineering and Energy Resources department at Siemens Corporate Technology (CT) in Moscow. A key area that Bartenev’s team is focusing on is the modernization of old oil-drilling facilities in Russia. Here, the team has succeeded in gaining the state-run oil company Rosneft as a research cooperation partner. Rosneft, Russia’s leading oil producer, extracts about 110 mill. t of oil annually and has a workforce of 75,000 people.

Acidic Foam. Siemens engineers Dr. Vitaly Malinin and Dr. Stepan Polikhov, who work in Bartenev’s department, have been specializing in oil-deposit cleaning techniques. Together with RN-Ufanipineft — a research institute operated by Rosneft in the city of Ufa near the Ural mountains — they have developed an efficient, cost-effective method for increasing the oil-flow rate in the near–borehole zone of an oil reservoir. The technique uses a foam consisting of water, hydrochloric acid, and other chemicals.
The method is based on a long-applied technique for cleaning oil wells. It involves use of an acid solution to dissolve impurities, such as calcium, gypsum, and barium sulfates, which are found in oil-bearing sediments and would otherwise block the flow of oil into the borehole. The reservoir is first flooded with the solution, which is then pumped out and the affected rock is washed with water. Without this treatment, which is normally carried out once every two to five years, the product extracted from roughly one million boreholes, which yield 30 billion barrels annually worldwide, would be around 30 % less. Still, the cleaning method’s effectiveness hasn’t entirely measured up to expectations so far. "When you use an acid solution alone to clean the reservoir rock of an oil deposit, you often find a large portion of the chemicals don’t necessarily get into the places you want them to be in order to eliminate the blockages," says Bartenev. That’s because when the solution flows into the borehole, part of it disappears into layers of sediment where it just isn’t needed.
While researching the process of multi-phase filtration, specialists from Siemens Corporate Technology found a way to ensure that the solution gets to precisely where it should be. "This foam that’s pumped into the bore hole in the first step seals off most of those areas of the underground reservoir that don’t need to be cleaned, but which nevertheless soak up large amounts of the solution," said Bartenev after extensive computer simulations.
After just five months of work, and with the help of computer systems from Siemens CT Russia, research was completed in February 2008. As Bartenev explains, the results not only provide a solution to flow-process problems; the numerical calculations also were supplemented by development of an analytical model that gives researchers a better understanding of technological aspects of the cleaning process. Rosneft has been using the results since the spring of 2008. "The new solution has provided us with deeper insight into how to lower the permeability of the highly porous sediment segments, and into how the acid mixture reaches exactly those areas where blockages need to be eliminated. Then the oil flows more easily to the pump," Bartenev reports.
In order to be able to investigate the effect of the acid-foam solution, Bartenev’s team obtained extensive data from Rosneft on borehole depths, permeability, pressure ratios, and flow rates, which the state-run company had systematically gathered and kept at its oil fields. "Thanks to all that data from the boreholes, we were able to develop a detailed analytical model for foam-acid treatment," Bartenev says.
The Foam method does not return extraction levels to the average value achieved at new wells — around 700 barrels per day, with an average Rosneft well producing only about 100 barrels of oil per well — but It has been confirmed, however, that the new model does result in a significant increase of oil production compared to conventional chemical cleaning methods.
After monitoring 27 wells, the researchers determined that conventional acid cleaning resulted in an average increase of only 8.6 t in the daily flow, while the foam-plus-acid technique boosted it by an average of around 17 t. In addition, the sealing effect of the foam method means that it requires the use of fewer chemicals. This not only yields savings in time and money; it also helps to protect the environment.

More Projects Planned. Because CT researchers were able to benefit from the practical experience of Rosneft’s staff, as well as from the company’s extensive data, "we succeeded in obtaining valuable new knowledge in the field of foam-acid treatment. This allowed us to clearly demonstrate our capabilities, which will serve as an excellent foundation for future business relations with Rosneft," says Bartenev. "In fact, we have already begun talks with the aim of intensifying our cooperation on efforts to substantially improve equipment used in oil and gas industry automation systems."
Another area of activity that the partners are looking into is extraction of oil from oil shale, for which a feasibility study is already under way. Rosneft is also optimistic about the success of the partnership. "The work we accomplished together was very stimulating for both sides," says Vladimir Savichev, head of Production, Development, and Research at the research center in Ufa. "We have been able to exchange concrete, specialized knowledge while combining the strengths of Siemens CT Russia and RN-Ufanipineft. That has shown us how we should be moving forward in the future."