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Heading for the Turonain Gas. New Gas Reservoirs are Being Developed in Russia

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Severneftgazprom appears to be closing in on its goal of increasing total gas production in 2012 up to 115 billion cubic meters at its Yuzhno-Russkoye field in Yamal. And that's just a start. Severneftegazprom has been hard pressed to turn around declining production at Yuzhno-Russkoye considering the gas field's importance as the source of throughput into the Nordstream Pipeline to Europe.

But its first test well, which combines multi-directional drilling with dual completions technologies, foreign and domestic, has born first fruit in producing gas from shallow Turonian layers that until recently were ignored given their complexity.

Severneftegazprom and Nord Stream invited Oil&Gas Eurasia in summer to the Yuzhno-Russkoye field to show the results of its work, and those of the contractors involved in the project including: Halliburton, TyumenNIIgiprogaz, Gazprom Bureniye, Korvet, and the plant GROM (Tyumen).

Total reserves of the turonian gas of West Siberian fields amount to approximately 3 trillion cubic meters and the fields of this region provide the bulk of potential supplies for Russian gas exports to Europe (approximately 80 percent). As the Cenomanian reservoirs (from which most of Russia's gas is produced) gradually deplete, further exploration and development of the more shallow Turonian level reserves are becoming a top-priority in Russia. Turonian rock is softer than shale, thus easier to produce than shale. But it is harder than the source rock found in Cenomanian layers. Thus, it presents its own problems.

Beginner's Luck

The project to produce gas from Turonian strata at Yuzhno-Russkoye field is currently in the “pilot” stage and is a first for Russia. Never before have Russian producers succeeded in tapping into these layers. There were several previous attempts to produce gas from Turonian reservoirs in Russia, but first experiments did not meet expectations. At Vyngapurovskoye and Lenskoye fields, Gazprom Dobycha Noyabrsk attempted to get to the Turonian zones using conventional vertical Cenomanian wells, which are traditional and optimal for the Cenomanian pools. But these were absolutely unsuitable for the Turonian because of the low production rates (approximately 10,000-18,000 cubic meters per day, which is significantly lower than the breakeven level in terms of ROI).

At that time, no one considered the option of either drilling directional and sub-horizontal wells (techniques which are now being used in the Yuzhno-Russkoye pilot project), or applying enhanced gas recovery technologies, so the projects on development of the gas fields were literally focused only on the Cenomanian. It was planned initially to exploit the upper zones and later switch over to the deeper ones. However, due to the demand for hydrocarbons, these plans were corrected as the production from the Cenomanian pools went into deeper decline.

A key factor was that the Yuzhno-Russkoye field was selected as the mineral resource base for the Nord Stream gas pipeline, by which Russian gas is transported along the Baltic Sea bed to Germany and farther to Europe. Investors took an interest in the great volume of reserves of this unique field.

And in Russia's Far North, there appears to be a lot of Turonian gas. The volume of Turonian gas in the Yuzhno-Russkoye field exceeds 300 billion cubic meters. In the Kharampurskoye field to the south of Yuzhno-Russkoye (the license belongs to the Rosneft subsidiary RN-Purneftegaz) there is 800 billion cubic meters. The Turonian deposits contain approximately 10-15 percent of the total reserves of Russia's Far North fields. Three trillion cubic meters is a very rough estimate of the total gas resources of West Siberia.


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Difficult is Not Impossible

The main difference between producing from the Cenomanian versus the Turonian is the degree of complexity of gas reserve recovery from these different formations. The picture on page 20 shows data on the main parameters of gas from the Turonian and Cenomanian reservoirs.

The Cenomanian gas belongs to the Cenomanian stage of the Upper Cretaceous. This stage was formed approximately 97.5 million years ago and is located at a depth of 900-1,750 meters. The Cenomanian reserves are classified as the easiest-to-recover, since their reservoirs are formed by sandstone compacted at a high pressure, which in turn predetermines a high productive capacity of the reservoir.

The Turonian gas occurrence is shallower – 750-1 050 meters, but the source rock is composed of the sandstone with a high content of dense rock admixtures (shale, siltstone), properties, permeability and gas saturation. Development of the Turonian pools entails the following problems:

● Poorer reservoir properties and, as a consequence, low well productivity;

● Significant reservoir heterogeneity and facial variability along the section and area-wise, which complicates the process of insuring uninhibited gas flow from the source rock;

● Low formation temperature and abnormally high formation pressure which requires well operation in hydrated mode.

Cenomanian and Turonian gas is classified as “dry” – it consists of pure methane by 97-99 percent facilitates processing, but also improves the efficiency of production and further marketing.

The composition of gas from the Yuzhno-Russkoye field is ideal. Thanks to the Cenomanian gas volumes and high productive capacity of the reservoir, the Company reached planned production levels of 25 billion cubic meters per year in 2010. By adding the Turonian reserves, Severneftegazprom expects to move that target this year to 26 billion cubic meters and even further when a second well is drilled in 2013.


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The Unique Experience №174

Pilot development of the Turonian was started on experimental well № 174. This well has a dual lateral design with low-angle bottomhole sections, which provides sufficient drainage radius and efficient recovery of the gas reserves along the section (see Fig. 1). This well design makes it possible to produce gas simultaneously from two reservoirs – Cenomanian and Turonian. It provides the opportunity to use one infrastructure for “double” production, which enables a significant cost reduction – the company is saving mostly on the lease of land area used for field development. From the ecological standpoint, humancaused impact on the environment is also decreased.

The uniqueness of the Yuzhno-Russkoye field project is that the company’s specialists used the “one site – two wells” principle.

As stated above, Severneftegazprom undertook the task of the maximum possible application of the domestic experience in realization of their projects. “We are trying to use the equipment and services of domestic companies to the maximum degree, and construction of the Turonian well made no exception, though this well appeared to be unique for Russia. <…> However, within the framework of the project, we had to use a well completion system of the global oilfield services company Halliburton. A domestic company, e.g. Sibburmash (Tyumen), could undertake development of similar technology, but this work would take at least three to four years, without any guarantee of success of the tests. Meanwhile, using foreign technology for this project with account for appropriate engineering support appeared to be cheaper in any case,” noted Evgeny Davydov, head of the drilling department at Severneftegazprom.

Severneftegazprom contracted a number of domestic companies including the following: TyumenNIIgiprogaz which prepared a detailed engineering design for the field, Gazprom Bureniye (drilling operations), Korvet (Kurgan) which jointly with Severneftegazprom manufactured a unique dual christmas tree used for commingled production from two zones. A spider-elevator for simultaneous running of two strings of tubing was designed by the plant GROM (Tyumen).

However, expertise of foreign companies appeared to be of some use for the project. Halliburton provided its system of dual completion which is designed for independent production from different zones through separate strings of 73-mm tubing. This system enables completion and survey operations separately in each hole of a multilateral well, and also enables separate access through the tubing to the main and lateral holes of the multilateral well. This same technology was applied for construction of the first Russian experimental dual bottomhole well №174 with low-angle bottomhole sections intended for Turonian pool development.

“Previous experience of the Turonian gas production showed that application of vertical wells (traditional for the Cenomanian zones) was not efficient due to low production rates, therefore it was necessary to look for innovative engineering solutions,” explained Stanislav Tsygankov. “We decided in favor of drilling of a dual bottomhole subhorizontal well with low-angle bottomhole sections. This experience is unique both in respect of the well design and the use of a special dual christmas tree and a spider-elevator for simultaneous running to two tubing strings in the well. Nobody has done this before.”

Next year, under the project on the further development of the Turonian pool in this field, it is planned to drill a single bottomhole production well №184. At present, there is a total of 143 wells operating at the Yuzhno-Russkoye field.


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New Starting Point

It is especially noteworthy that all operations at the field have been fulfilled in a very short period of time. Commercial operation of the Yuzhno-Russkoye field was started in 2007, while the construction of the field facilities and infrastructure on the whole was started only in 2006.

In 2010, gas production from the pool already reached the planned level of 25 billion cubic meters a year. In May 2012 the total gas production was increased uo to 100 billion cubic meters. By the end of this year this figure could reach 115 billion cubic meters. Fig. 2 shows the gas production profile for the Yuzhno-Russkoye field. After 2020 the production of Cenomanian gas decline will begin, the plateau will be maintained due to the start of development of the Turonian pool. In the future Company wants to produce about 5-8 billion cubic meters of Turonian gas per year. So, it will be possible to extend the level of the maximum production of 25 billion cubic meters until 2025–2030.

However, at present all these forecasts are very approximate. According to some estimates, Actual numbers will depend on current annual volumes and on the general geological situation at the field. But it is clear that the age of easy and cheap gas is over. So now comes the transition to the new stage of development of the gas industry, which involves field development in exstremely complex geological and natural-climatic conditions.

Source:Oil&Gas Eurasia

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