Ecological and geochemical monitoring of the Ob bay areas of test drilling carbohydrates Печать E-mail

Institute of Geochemistry and Analytical Chemistry RAS, JSC "MORNEFEGASPROJECV

Some water areas of the Kara Sea (the structures Kamennomiskay, Obskay, Chugoryahinskay) are not considered to be promising for petroleum and gas prospecting.

These areas also known as relatively cheap for pipeline and tanker transportation of carbohydrates. The search of gas in the Ob estuary has huge meaning for perspective development of national economy.

At the same time, the prospecting work, production and transportation of gas are subjected to a large risk of accidents and the environmental pollution, that causes a quite justified alarm concerning the future state of the Ob Bay ecosystems and the adjacent part of the Kara Sea. The Ob Bay belongs to productive zones of the Russian Arctic Region, therefore a complex ecological monitoring is the important of evolution of the existing situation in this region and can be used in forecast of the estuary system dynamics.

The monitoring design (sampling grid, the measurable parameters frequency of sampling) fitted to the international practice of similar investigations. Selection of parameters for ecological monitoring of the natural environment were selected on the basis of the previous experience within the areas for petroleum-gas production (the Mexican gulf Northern and Norwegian seas).

Field survey in the Ob Bay close to the drilling platform "Amazone" was performed using vessel "Kaliningradets". Ecological monitoring included two surveys at the test drilling sites named Kamennomysskaya and Obskaya Nol earned out at the beginning of the drilling process and on the last stage of the well test. To estimate the regional geochemical background parameters we used the data on chemical pollution of the samples collected on board the RV "Akademik Boris Petrov" during the GEOKHI RAS marine expeditions of 2002-2003 in the framework of the Russian-German project 'The Nature of Siberian rivers run-off and its behavior in adjacent part of the Kara Sea"(Stepanets. Borisov, 2003).

According to the program water and sediments were sampled in all azimuth directions (N, S, W, E) at a distance of 50. 100. 250, 500 and 1000 m away from the platform. Current background parameters were determined 3000-5000 m windward from the platform.

Hydrophysical and hydrochemical water properties (t, pH, Eh, O2, etc) were studied on board, hi laboratory samples were analyzed for heavy metals by XRF spectrometer "Spectroscan" (bottom sediments) and ICP-AES installation after preconcentration of microelements on chelate sorbents with amino-carboxylic groups (water samples). Petroleum products and anionic surface-active compounds were determined in concentrates after extraction using fluorometer "Fluorat-02". Anthropogenic radionuclides (gamma-emitters) were detected with the help a low background gamma-spectrometry installation using Ge-detector.

Experimental data processing enabled to estimate concentration and spatial variation of the determined parameters during drilling.

Noticeable variation in pollutant content was registered for heavy metals. For example, the lead anomalous zone appeared to be local area stretching from the platform for approximately 100 m downstream. Selected background and anomalous water samples were analyzed in more detail for elements1 speciation forms. To study heavy metal forms in river the Kara Sea water we applied a multi-stage filtration method, developed by GEOKHI RAS, based on fractionation of water components on membranes filters with pore sizes varying from 1 to 0.025|лп followed by mass-spectrometric heavy metal determination in the obtained fractions. A sample of 400 ml was enforced as cyclonic flow through the installation with concatenated one under another membranes with progressively size-decreasing pores (1.0: 0.45; 0.1; 0.05; 0.025 щи). At every level the liquid phase moved between the two filters one above another. Filtration reached 1.6-2.0 ml/min at circulation speed 0.2-0.6 ml/min. After the first complete pumping the sample was run through the closed space for 40 min. Such regime provides equilibrium conditions ensuring maximum penetration of the particles of the corresponding diameter (penetration coefficient close to 1). Extracted fractions accumulated in the corresponding cameras from which subsample was taken with syringe aliquot for the further mass-spectrometry of separate elements. The proposed method gives possibility to 40-times metal concentration due to water components' accumulation in the smaller volume of the particular fraction. This enables to study trace element distribution between particles of different size incase of a very low element content in water. Obtained data witness predominant soluble form of chemical elements in the open part of the Kara Sea. In water samples of the Ob Bay we observed a noticeable increase in metal content in suspended particles especially those held by membranes with smaller pores. Samples from the inner part of the Taz Bay were noted for considerable presence of the studied elements in coarser suspended fraction. No difference was found between the trace element distribution in fractions separated from the background and anomalous sites. However this can result from the difficult registration of minor effects at the low level of element content in water.

Surface water samples showed significant ab-modality in lead and to a lesser extent in cadmium. At the initial drilling stage such enhanced concentrations were registered in a radius of 250 m around the platform. By the end of drilling the zone of abnormal higher concentration of these elements embraces the area 500 m away from its center.

Significant excess of oil products was found in the top layer of a number of bottom sediment samples as far as 250 m away from the platform in the north-western direction (downstream). In water samples enhanced oil product content was registered in the 100-m radius around the oil rig. Higher values were determined in the bottom water samples due to lower mobility of the deeper water masses in absence of the wind-induced wave.
It is worth noting that reliability in interpretation of the oil products content in sediments and water in particular depends upon the maintenance of temperature and transportation conditions during sample storage before the laboratory analysis. Our study of the kinetics of the oil product and surfactant species destruction in water solution performed at room temperature showed that approximately 65 % of oil products dissociated within the first 4-5 days, the rest stabilizing in the next 4-5 day period. Anion surfactants decayed practically completely during a number of days.

No definite effect was found for redistribution of the anthropogenic radionuclides that could result from sediment roiling due to deposition of the upper layer material from the oil well. Radiocesium content in bottom sediments taken during drilling is comparable to its specific activity in samples taken after drilling.

The ecological and geochemical studies in the Ob Bay areas of test drilling revealed technogenic contamination of the environment due to drilling activity and enabled to estimate its spatial and temporal variability in the impact zone of the basin. Local environmental contamination with chemical substances (oil products, heavy metals) was registered during drilling process accompanied by fuel, oil and working grout spills. Horizontal and vertical turbulent diffusion, wave action in the study area decrease enhanced pollutant concentration down to background values in a rather short time period.
Content of contaminants in the abnormal samples was considerably lower compared to permissible levels. This showed observation of the main ecological requirements during drilling in the study area. For example, all sludge and drilling water formed were collected as accumulated and transferred to production supply vessel with further removal and utilization at a specially appointed site.

Such ecological studies enable to use chemical contaminants as tracers of the environmental processes and to forecast spatial and temporal distribution of admixtures in case of emergency. Complex approach in investigation of the anthropogenic contamination of water media with simultaneous study of the background environmental parameters enabled to reveal parameters of the technogenic contamination of the test drilling areas of the Ob and Kamennomyssk licensed sites of the Ob Bay and to estimate its impact on the Ob basin and the adjacent Kara Sea area.



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