V.P. KONUKHIN Kola Science Centre of the Russian Academy of Sciences, Russia

1. Introduction

By estimation of the Ministry of Natural Resources of RF and "VNIIOkeangeologiya" (Research Institute of ocean geology) the total resources recovered in peripheral seas of Russia on the whole, as of July 1, 2003 amounted to over 13,5 bln.ton of oil and about 79 trim3 of gas. The prospected resources of oil and gas on the Arctic shelf of Russia make about one third of these resources.

However, the real development of hydrocarbon raw materials deposits of Arctic seas requires a large number of complex technological problems to be solved, they are connected with special climatic conditions of the region and ice conditions in the considered water areas. One of such problems is to provide transportation - distribution systems.

In author's opinion, the efficiency of transportation-distribution systems for oil and gas in the Arctic can be increased considerably, if their structure would include underground storage plants, located in the coastal geological formations

There are quite realistic prerequisites for the handling of the issue of underground storage plants in the conditions of Russia's Arctic. The basic prerequisites are:

? high experience in construction and operation of under-ground oil-and-gas
storage facilities in Scandinavian countries whose engineering-and-geological conditions are close to those of the Kola Peninsula. Karelia and some areas of the Arkhangelsk region; as well as the first Russian experience in the field under consideration:
? geological formations and rock masses in European northern Russia, suitable for placement of underground tank fleets of great capacity;
? tested technologies and experience of fast construction of large underground complexes including underground structures of up 700 nr in cross-section in rock and permafrost in Russian Arctic.

2. Utilization of underground complexes for storing oil and gas in Scandinavian countries.

In Finland, Norway and Sweden there are built and utilized about 250 storage facilities for oil and oil products, their capacity being over 50 mln. m. All of them are placed in high-strength crystalline rocks of Fennoscandia, which makes it possible to avoid using costly reinforced concrete lining.
A typical example of such storage facilities is the Finnish oil storage in Porvoo. Its first stage with the capacity of 677000 m was built during three years, the second stage with the capacity of 495000 m still took less time to be built. Small underground storages, for instance, in Lahti with the capacity of 180000 m3 were built in one year.

Let us note some of important technological approaches, adopted in Scandinavia for storing oil in underground reservoirs:

- storages are built at such depth, that the pressure of underground water at any point of the contour of working would exceed the head pressure of the product stored.
- the necessary temperature when storing oil is kept up using a water bottom, the content of which is heated via heat exchangers.

For gas storages, considering its pressure, the depth of the storage is rather important. To prevent leakage through fractures and cracks, the hydrostatic pressure of underground water should not exceed the interior gas pressure.

3. Engineering - geological conditions of the construction of underground oil and gas storages in the Russian Arctic

The most probable placement of storage plants for accumulation of oil and gas in transportation- distribution systems of the European north of Russia will depend on places of their loading in tankers in the area with non-freezing sea ports, located on the Barents sea coast of the Kola peninsula.

Let us consider the engineering-geological conditions of construction and exploitation of this zone in more detail.
The Kola Peninsula makes part of the Baltic Shield - a vast area of ancient stabilization of the Earth's crust.

It is indicative that new tectonic disruptions in the northern zone of the Kola Peninsula formed approximately orthogonal system of blocks with faults miming northeast and northwest.

An acceptably prognosticated level of possible earthquakes in the considered region does not exceed 4-5 points (with 10 point system).

Since the northern coastal line of the Kola Peninsula is formed with neotectonic terraces, the most favourable sites for building underground complex facilities in this region are located at a certain distance from the Barents Sea coastline.

The best ones from the point of view of steadiness of underground facilities, are believed to be the large granitoid massifs of Litsa-Uragnba complex of the early proterozoic age, where systems of "young" fractures are not dominating- whereas in zones of ancient disruptions, the recrystallization and high-temperature metasomatism, turned in migmatizing, resulted in "healing" of permeable zones of Precambrian.

There are good chances to expect that region of Dalnyey Zelentsy and Teriberka will, in fixture, be chosen for placement of large underground storages of oil and gas.

As an example, we can cite the characteristic of one of the rock massifs making part of the Murmansk geoblock and located in the coastal zone.

The massif is formed of plagio-microcline biotite migmatite granites with medium grain porphyry-like homogeneous texture. The granite massif is limited with zones of Assuring , cured at depth. There are several systems of fissures with an average distance of 150-700 m between them.
The compression resistance in rock samples is 148 Mpa, whereas the tensile strength is 8,3 MPa.

Hydraulic parameters: filtration coefficient at depths before 150 m - n x 10 -3 m/day, at depths 150-160 m - n x 10-4 m/day.

Practice shows that when choosing location for placing underground oil and gas storage facilities great importance is given to the search of monolithic structural blocks in geological formations. Our investigations show, that such blocks can be found in many parts of the coast.

When considering the coastal zone of the mainland part of Arkhangelsk region and islands in the Arctic Ocean, especially the massifs of permafrost, including hard rock, attract the researchers.

A typical feature of these rocks is having ice inclusions in them. At the same time all natural fissures are filled with ice or dispersed, ice-saturated rocks.
When estimating the bearing capacity, stability and deforming properties of the permafrost massifs, surrounding the underground working, they are considered as a complex mechanical system, consisting of natural mineral rifts, blocks and layers of different size and form, cemented by the ice or ice-saturated disperse formations.

With abundant ice inclusions rock slumping occurs as a result of defrosting, thus inducing a sharp differentiation of loads on the lining of underground facilities.

Henceforth a conclusion follows, when designing underground facilities, to be placed in permafrost massifs, one should know the character and intensity of all forthcoming changes of temperature regime in the massif as well as the extent and configuration of defrosting zones, formed in the process of construction and exploitation of such facilities, as making a cavity in the massif brings in sharp perturbations in the temperature field, relatively uniform before.

4. Equipment and technologies of building large-scale underground facilities in conditions of Russia's Arctic.

When building underground facilities in the harsh conditions of the Arctic and adjacent regions planners and builders had to face the necessity of accomplishing a number of new technical and technological tasks, since traditional energy consuming technologies of mining works, which implied keeping positive temperatures in workings, resulted in considerable problems and the higher total costs of the construction.

A number of new technologies are connected with involvement of surrounding rock massifs in the joint process with lining and purposeful control of properties and the general condition of those massifs.

When using anchorage and concrete sputtering for mounting the large, scale underground facilities in conditions of negative temperatures a number of specific technological requirements were observed, while in cases, when the surrounding rock massif was represented with fractured permafrost rocks, the construction of combined support should have certain flexibility.

We have to note that the modem technologies of building concrete sputtering lining make it possible to apply the concrete sputtering at the negative temperature of rock surface and the surrounding air inside a working up to - 102C. With temperatures below - 10°C, the heating of the pre-contour zone to the depth, which provides the calculated rated conditions of concrete indurations.

In workings with negative temperatures of rock and air , additives, preventing the concrete from freezing are included in the compositions of concrete.
The fastening of arches of chambers using monolithic reinforced concrete. Four methods of concreting have been used in the practice of underground construction in the Russian Arctic.

- laying of concrete into the heated curb with mixture indurations until the specified strength in the process of slow cooling down of the laid concrete;
- thermos method, the basis of which is the maximum possible keeping and utilization of heat, released during the aquation of cement;
- method based on inclusion of anti-gel additives into concrete mixtures;
- method using additional heating using thermo-active forms.

The choice of production method for concrete works, during the lining construction was earned out on the basis of technical and economical comparison of variants, taking into consideration energy, work and materials costs, as well as depending on the parameters of specific lining construction, thermo-physical characteristics and thermal regime of the peripheral rock massif.
The cost of 1 m³ of prepared amounts for large-scale underground facilities varied between USS 86 to 120.

5. Conclusion
The analysis of practice of underground reservoirs utilization for storing oil and gas in Scandinavian countries, having engineering and geological conditions similar to the ones of north-west of Russia, as well as the assessment of specific conditions and experience of underground construction in the Russian Arctic allows us to draw some conclusions:

1. When building oil and gas transportation and distribution system in the European north of Russia it is expedient to include in their structure underground storage facilities for oil and gas, in particular, in places of reloading of those products in tankers. This refers to petroleum refineries and companies for liquefaction of gas

2. On the coast of the Kola Peninsula, mainland part of Arkhangelsk region and in islands of the Arctic Ocean, geological formations, separate massifs of hard rock and sites, fit for placing high-capacity underground oil and gas storages can be found.

3. There are efficient and approved technologies of construction and maintenance in stable and safe condition during a long time of large scale underground structures, acceptable in conditions of the Arctic and Far North of Russia from the economical and ecological points of view for building underground reservoirs for oil and gas in the considered region.

References.

V.P. Konukhin Outlooks of utilization of underground reservoirs of transport-distribution systems of oil and gas in the European North of Russia. Proceedings of the 4-th international forum. Fuel and energy complex of Russia. Regional aspects. //S.-Petersburg. April 6-9,2004, p. 94-98.
VKonukhin The construction of the large-scale underground facilities in the Russian Arctic. //Proceedings of International conference "Underground works: ambitions and realities", October 25-28, 1999, Paris, p. 239-244.
Vladimir P. Konukhin Study of the Effect of the Mining Operation on Crystalline Rock Mass During Construction of Spent Nuclear fuel and High Level Waste Storage Facilities in the Russian Western Arctic. //Proceeding of a European Commission Cluster Conference. November 3-5,2003, Luxemburg.
Konukhin VP. Support of large-dimension underground structures. //Kola Science Centre Publ. RAS. -Apatity, 1991. 146 pp.
Konukhin VP, Control over properties and state of the rock masses in construction and operation of underground structures. //Kola Science Centre Publ. RAS. -Apatity. 1992.
Installing oil and gas platforms in the Northern sea. //Kola Science Centre Publ. RAS. -Apatity. 2001. 87pp.

ARCTIC SHELF OIL AND GAS CONFERENCE 2004