Dependence of Vankor oilfield soils deformation characteristics on their physical properties

Kotov P.I., Tsarapov M.N.

Lomonosov Moscow State University, Moscow, Russia

kotovpi@mail.ru

Permafrost conditions of Vankor oilfield are poorly understood. In the literature there are no regional data on the mechanical and deformational properties of frozen soils during thawing. The development strategy of "Rosneft" provides integrated development of oilfield area, the construction of engineering structures and pipelines, therefore the study of physical and mechanical properties of soils is an important task.

The investigate area is located in a continuous permafrost. The area is an example of a flat, accumulative plains composed of unconsolidated Quaternary sediments. Research of major genetic types of soils (sandy loam (la IIIkz), сlay loam (a IIIkr)) were performed in the laboratory. We have performed about 100 tests to determine the compression and thawing coefficients in accordance with GOST 12248-96. Statistical analysis of the obtained results was performed in accordance with GOST 20522-96. After this, we analyzed the pair correlation of compression and thawing coefficients depending on the physical properties of permafrost soil (moisture content, density, porosity coefficient, plastic index) for the detection of deviations and selecting the most informative characteristics. Next, the empirical distribution of the deformation characteristics of soils and the multiple statistical analyzes was performed. Data analysis have been considered depending on the coefficients of thawing and compression of the various combinations of two, three and four indicators of the physical properties of soil. The final selection of optimal variants of prediction equations was performed by testing the parameters of these equations on an additional (independent) experimental data. The final choice of two predictive equations for determining the coefficient of compression and thawing was made according to results of control test.

Using this method will allow to make a better choice of construction area, will help to reduce the number of laboratory and field test of the deformation characteristics of soil, a more rational planning of engineering and geological surveys.

References:

1. GOST 12248-96 Laboratory methods for determining the characteristics of strength and deformability.

2. GOST 20522-96 Methods of statistical processing of test results

Scientific basis of engineering geocryological monitoring for gas pipeline "Bovanenkovo-Ukhta"

Lashina N. V.

Lomonosov Moscow State University, Moscow

lashinanatalia@gmail.com

Gas transmission facilities and associated pipeline infrastructure, "Bovanenkovo - Ukhta" built on an unprecedented complexity of permafrost conditions. Experience in the construction of large industrial facilities in such complex engineering and permafrost conditions in the world is missing. In this regard, especially important to monitor the dynamics of permafrost soils in the foundations and stability of buildings and structures during construction and operation to destabilize the timely identification of processes, development and implementation of preventive measures for their prevention, as well as operating time experience in the construction and operation bases and foundations in especially difficult permafrost conditions.

The construction and subsequent operation of the pipeline in permafrost will lead to neoplastic and activation of permafrost processes developing in the soil in the zone of direct interaction with the pipeline, and on the surrounding area, due to a broken pipeline. These processes can have a significant impact on the performance of the pipeline and cause of his accident, as well as disrupt the ecological sustainability of the natural environment geocryological.

However, the patterns of human dynamics of natural and technological systems in different environments is still poorly understood. Knowledge of them is a prerequisite for the drawing up of scientific studies forecast the stabilization and rehabilitation engineering geocryological situation. To ensure stability and safe operation of gas pipelines in difficult engineering and permafrost conditions requires organization and a permanent monitoring system (engineering geocryological monitoring). But the current practice of organizing the monitoring is usually limited to only control the state of the pipe, and virtually ignores the natural conditions of its distance and its changes during construction and subsequent operation.

Engineering and geocryological monitoring is an integral part of environmental monitoring, which aims at a comprehensive assessment of changes in the atmosphere, hydrosphere, biosphere, geological environment.

When creating and maintaining engineering geocryological monitoring should take into account the main technical solutions specific structures adopted in the project: the principle of use of permafrost as a foundation, particularly thermal and mechanical interaction with the ground base, allowable values of bearing capacity and deformation of the base facilities, environmental requirements, etc .

Engineering and geocryological monitoring should begin in building up period when monitoring network formed the background for the assessment of the situation geocryological.The results of monitoring during this period are the source data to assess the changes that will occur during construction and operation of geotechnical systems. In the construction period, the organization carried out the observation network and run surveillance on construction sites.

Operational period on features of spatial development and the impact of varying degrees of anthropogenic impact over time can be divided into two stages: the initial - the duration of 3-5 years and the main - with 3-5 years of operation before the end of construction. In the initial period of operation of communication facilities with the environment is the most active and significant changes are possible geocryological situation and deformation structures. After 3-5 years of operation of facilities, there comes a relative dynamic equilibrium in the system structure - or the natural environment in this time taking the necessary steps to maintain the stability of the natural environment and the stability of structures [1].

At the same time at the moment has already developed a general scheme of organizing and conducting engineering geo-cryological monitoring, taking into account the co-expression of the features and specifications of facilities engineering geocryological environment [2], it includes: collection, processing and analysis; preliminary forecast and assessment of the territory; survey of engineering facilities and adjoining territories, organizing and carrying out works; processing Monitoring and evaluation of the dynamics of CTA, the current forecast of geocryological situation and permafrost processes, de-velopment and organization of protective measures, the organization of observations of the protective measures.

This scheme can be adopted as a basis for the organization of engineering geocryological monitoring the pipeline Bova-nenkovo-Ukhta.

In general, transportation of gas through an underground pipeline will be carried out at low temperatures. One of the important features of the pipeline, "Bovanenkovo-Ukhta," is that it will cross the waters Baidaratskaya Bay on the site about 70 km wide. In order to eliminate the possibility of freezing pipes, and their ascent from the bottom lip of gas transportation in this area will be at positive temperatures. Heating and cooling of the gas will occur at compressor stations located on both sides at a distance of 3 km from the area Baidaratskaya Bay. Coast Baidaratskaya Bay complex geocryological different conditions.

Exogenous geological processes in the study are as a rule, cryogenic genesis and developed quite extensively. In the natural environment in the aspect of the planned construction of gas pipelines degree of infestation area cryogenic processes and their genetic diversity is relatively low. However, the technogenic transformation of the territory subject to extreme activation of many exogenous processes.

Directly in the common processes of soil frost heaving, frost cracking of rocks and development of polygonalice wedges, thermokarst and deflation. In some places marked mild form thermoerosion and solifluction. At a location nearby the coast to the above processes are added volnopriboynoy thermal abrasion process, the active formation of advanced forms of gully thermoerosion.

Despite its uniqueness, the gas pipeline project Bovanenkovo-Ukhta does not include the organization of monitoring building up and construction period, which further make it difficult to operate. For the period of operation of the pipeline monitoring system Bovanenkovo-Ukhta developed, but, despite this widespread development of adverse factors, it is absolutely not justified: the network thermometric wells arranged not according to certain conditions, a purely mechanical way to the grid, snow survey is not provided, the kit includes all the same "grid" leveling of the pipeline. Observations of exogenous geological processes and phenomena is not provided.

According to the geotechnical monitoring services Vorkuta LPU MG, at the moment, even before the operation, construction along the strip there is active development of. Which can then lead to a dangerous or emergency situations, such as those that occur on pipelines in western Siberia.

Analysis of field and laboratory studies of the territory gas pipeline system revealed that a set of negative engineering-geological processes and the dynamics of their development are quite closely related to certain types of geotech-nical systems. As a consequence, first, the observations in the monitoring system can be concentrated within a selected representative of key sites that meet certain Geotechnical Systems (GTS), and secondly, the types of observations and rules of conduct will be determined by the geotechnical characteristics of the structure of the system.

To organize the monitoring of the study area can highlight key areas, including all of TCA. For each of the sites to deter-mine the direction of engineering geocryological monitoring, and has a corresponding direction to develop a network of observations of different processes, as well as a number of protivodeformatsionnyh events.

Such networking will allow a more qualitative observations carried out geotechnical monitoring, providing a complete picture of all the changes taking place in the GTS data.

References:

1. Ершов Э.Д.. Общая геокриология. Изд.: Московского Университета. Москва. 2002г. С. 325-343.

2. Основы геокриологии. Часть 6. Геокриологический прогноз и экологические проблемы в криолитозоне // Под ред. Ершова Э.Д. Изд.: Mосковского Университета. Москва. 2008г. С.657-699.