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On problem of interpretation and forecasting space-temporary variations of geophysical fields on results of deep scientific drilling
Esipko O.A., Kolbasova A.V., Rosaev A.E. In the process of boring the deep bore holes, as scientific, so and industrial one's living, and when processing the received results, the problem of large arrays of data analyses appears. In this connection, it is very important to use the modern mathematical methods for: + Forecast of rock properties under maximal depth, reached by drilling, for the reason of damages in the process of boring preventions, as well as practicability of the continuation of boring; + Allocations of the useful signal on the background of casual hindrances; + Optimization of methods of averaging (smoothing), allocations of uniform structured units, with provision for specifics geologic-geophysical studies. Information on bore hole A number of deep and superdeep wells have been drilled in Russia where a complex of geophysical surveys including temperature logging was carried out. The wells where all drilling activities have been finished but the research activities still continue are of a great scientific and practical interest for studying the present-day geological processes taking place in the Earth's interior. Vorotilovo deep well (VDW) is one of those wells-geolaboratories. Well data Vorotilovo deep well is situated in the central part of the Russian Plate, 75 kilometers to the north of Nizhniy Novgorod, on the left bank of the Volga River, in the central part of the Puchezh-Katunki ring structure [1] (Fig.1). The depth of the well is 5374 m, the temperature at the bottom is 95C, and the pressure is 63 MPa. Well design Direction 720 mm 0-65 m Conductor 508 mm 0-689 m Open borehole 295.3 mm 689-1752 m 215.4 mm 752-5374 m To the depth of 670 m the drilled section is composed of sediments of overlying and coptogenic complex. Below, down to the borehole bottom, it is composed mainly of Archaean and Low Proterozoic gneisses, amphibolites, crystalline schists that make up a socle complex. While drilling the core was obtained within the depth interval of 1481-5360 m (core recovery 75%, core diameter 60 mm). In order to study the upper part of the section the satellite well with the depth of 1498 m was drilled in immediate proximity to the VDW. On the basis of the two wells the geolaboratory was put in operation where, since the year 1994, the regular observations of geological-geophysical fields are being carried out. The research complex The main peculiarities of research activities conducted in the VDW are: relatively short time period of drilling; uncased borehole from the depth of 689 m to the bottom; long dwelling time period; high level of geological-geophysical knowledge of the ring structure area and of the section tapped by the deep well; remoteness from the strong sources of noise.


Fig.1 Position of Vorotilovo Geoobservatory According to specially developed program, since 1994, in the VDW the regular observations are being carried out in order to study the variations, the nature and the properties of modern physicochemical fields of deep horizons of the Russian Plate, their interaction and the influence they have on the biosphere. The subjects of inquiry are the fields and environment properties including thermal, electromagnetic, acoustic, radioactive properties, chemical and gas composition of the fluid, deformation mode of environment, ground biocenosis. The geological fields had been studied within 8 years (1994-2001). The well survey by approved complex that included temperature logging, mud receptivity logging, electrical, magnetic and nuclear logging, caliper and section gage logging, interval sampling of fluids for chemical, gas and microbiological analyses were carried out regularly (2-4 times per year); the static level of ground waters is measured every day. In 1997 (October-November) 7 geophysical survey complexes were conducted with 7 day intervals. In 2000-2001 the experimental testing with continuous recording of temperature was carried out within 6-8 hours. The example of geophysical data development As an example of with depth and variation log data with 0.2 meters of (verified) data. As a geophysical data development, the variation of magnetic susceptibility of borehole diameter at Vorotilovo geolaboratory are performed. The step at different dates are used. So finally, we have a very large array main feature, the variation of magnetic properties shows (quasi-)


harmonic dependence from depth (Fig. 2). The original algorithm for periodicity detection [2] is used for this dependence studying (table1). The good mathematical approximation of this data is very important for any physical (or geophysical) model constructions and for the prediction of geophysical parameters variation under the maximal depth. In spite of the certain success in solution of the declared problem, the need for the improvement of mathematical methods of the test of data exists. Smooth interval, meters 500 400 300 200 Period, meters 2400 1924 1818 1363 ±175 ±70 ±86 ±63 Reference: 1. - . /. .., ...- -, .- 1999.-392 . 2. .. . // . V , 26-27 . 1996 ., .- .,1996.-.31-33. Amplitude 0.004 0.003 0.005 0.008


Fig.2 The magnetic susceptibility and well diameter depth dependence (VDW)