Influence of exogenous factors on deep heat flow

Abstract

to this region since2006. Measurements were made using a GEOSMtelemetric multichannel probe [1].Most of the works were carried out in the areas ofKnipovich Ridge and the western Svalbard Plate. During the expeditions, 66 new heat flow values wereobtained and they have convincingly shown the relationship between the geothermal field and the locations of hydrocarbon fields [2].In the 28th cruise of the R/V, the study area was thesouthwest Barents Sea. Heat flow measurements at theFedynski swell, at a depth of no more than 300 m, haveindicated the very intensive influence of exogenousfactors on the deep heat flow. The influence of seasonal periodic oscillations of temperature at the seafloor due to insolation was identified, as well as that ofhighdebit nearbottom currents. This factor is especially noticeable in the southern part of Barents Sea,where the influence of the Norwegian–Kola branch ofthe Gulf Stream is detected. With respect to this,direct probing did not allow conditional estimates ofdeep background heat flow to be obtained, because itwas problematic to separate the deep geothermal gradient from the background of intensive exogenoustemperature anomalies (Fig. 1a).To obtain the conditional values of heat flow measurements for water areas, areas of great depth (morethan 500 m) and with no strong nearbottom currents,i.e., those where an isothermal nearbottom waterlayer is formed (Fig. 1b), are preferred for study. However, the predominant part of the shelf zones withinthe Barents and Kara seas, where these conditions areabsent, remains promising for hydrocarbons. So, further geothermal studies in these areas are necessary.Geothermal studies help determine the depth of thecatagenetic temperature interval (110–180°C), whereorganic matter transforms into hydrocarbons. In addition, all the gas and oil deposits are already explored inthe Barents–Kara region coincide with the geothermal anomalies that can be considered as one of prospecting indicators. The influence of exogenous factorsin studies of this kind should be taken into accountusing model corrections or by measurements at depthsbelow the “neutral layer.”In practice, study of the geothermal regime of theshelf zone was based on analysis of experimental datacollected in the contact zone between water and bottom sediments [3, 4]. To calculate the temperaturecorrection at this boundary or the depth of the “neutral layer” (where the exogen ous factor does not affectthe results), we should have regular observations of thenearbottom temperature for several years. Since thereis a developed hydrological network in the Russianpart of the shelf zone (hydrological stations measureproperties of water in different layers) [5], the basis forsuch a calculation is available.The defect of the methods mentioned in the literature is that the input data for formulas (more precisely,the amplitude and oscillation period) are set from thestatistical estimates, which imposes a certain error onthe resulted model. Of course, this is not a good point,because the amplitude and oscillation period are thedestination parameters. To eliminate these defect, themethod of harmonic analysis is proposed.In the expansion, the function is written in theform of a trigonometric series [6]: