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The paper deals with one of the highly relevant problems arising from disposal of produced waters in West-Siberian oilfields. Produced waters are those co-recovered with oil. The water-cut factor (for oil) is well-known to reach 90% in West Siberia. This has led to widespread events for disposal of produced waters. Improving the procedures for prediction calculations of admissible quantity and quality of disposed waters is a topical problem in petroleum hydrogeology in West Siberia. This study reports a leak-off coefficient estimation for the Cenomanian deposits (the target ones for disposal of produced waters in most of oilfields across the region) of the Mesozoic hydrogeological basin. The calculation procedure widely used at present for a homogeneous confined aquifer does not reflect the true natural picture, as the aquifer into which the produced water is pumped is multilayered and heterogeneous. Here we look into natural processes for the formation of the West-Siberian megabasin, which have resulted in heterogeneous reservoirs: uncompensated sediment accumulation and present vertical fluid migration channels. Here we show that the gross thickness of the aquifer should be employed in leak-off and hydrodynamic estimations, and adduce the leak-off coefficient estimations for five oil wells in the West Salym oilfield based on the procedure suggested herein (factoring in the multilayered nature of the Cenomanian deposits). The average leak-off coefficient of sand streaks was 0.298 m/day, which we believe to reflect the natural condition of the aquifer more adequately than the standard estimation procedure used for a homogeneous confined aquifer.

Here, we reported on experimental studies related to the exposure of oil to a 50 Hz electromagnetic field (0.81 T strength) and examined the changes in the geochemical characteristics of oil: n-alkane distribution, isotopic composition (δ13C), and concentration of paramagnetic centers. We discovered that electromagnetic fields have impacts on the distribution of n-alkanes and on their individual isotopic composition, with the concentration of paramagnetic centers remaining unchanged. While discussing the results, we looked into the state-of-the-art of research on electromagnetic exposures of the bottom-hole formation zone and into natural electric and geomagnetic fields. We consequently hypothesized that natural geomagnetic fields can influence the geochemical evolution processes of oil. This hypothesis requires further studies to reveal the frequency and strength characteristics of natural geomagnetic fields.

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