Isolation of Dolerite Intrusions by Borehole Magnetometry to Refine the Lithological Section of the Timan-Pechora Super-Deep Well

Abstract

Summary The intrusions represented by gabbros - dolerites and dolerites of various structures in terms of magnetic susceptibility and magnetic field clearly stand out among the effusive-terrigenous and carbonate-terrigenous sediments of the Paleozoic Timan-Pechora super-deep well SG-5 (Timan-Pechora oil and gas province). In the conditions of a sedimentary section, the use of borehole magnetometry at depths of more than 3.5 - 5 km allows us to determine the actual position of dolerites in the section, their depth and thickness. Methods: for magnetometric studies at the Institute of Geophysics, Ural Branch of the Russian Academy of Sciences, inclinometer and magnetometers were developed that allow continuous measurements of the magnetic susceptibility of rocks (?), the vertical component (Za) and the entire vector of the horizontal component (H) of the geomagnetic field; magnetic azimuth (Am) and zenith angle (f) of the well. The technique for processing and interpreting the magnetic properties of dolerite intrusions was also developed at the Institute of Geophysics, Ural Branch of the Russian Academy of Sciences. Results: the possibilities of borehole magnetometry method for studying the magnetic properties of dolerite intrusions and clarifying the lithological and stratigraphic characteristics of the Timan-Pechora super-deep well (SG-5) for assessing the oil and gas potential of the Silurian - Lower Devonian deposits at a depth below the gas condensate reservoir. Conclusions: the magnetic properties of dolerite intrusions in the natural occurrence are determined according to borehole magnetometry, namely, magnetic susceptibility, magnetic field and magnetization. A more accurate location of the roof and the bottom of dolerite intrusions was established, which made it possible to localize and determine their thickness in the section of the Timan-Pechora super-deep well at depths of more than 3.5 km. Keywords: super-deep borehole magnetometry, magnetic susceptibility, geomagnetic field, magnetization, dolerites, intrusions.