2 Volumes Final Proceedings - Washington 1984.pdf - IARC Research

egradient-pde uerficalgradientA5. OM?. ON AB400m. MtV=40mA MNBA6MIFIGURE 1 Results of resistivity logging.1) crack dolerites; 2) sand; 3) alteration of marls, limestones, dolomites;a) pk curve, gradient probe; b) Pkcurve, middle gradient installation; C)Pkcurve, vertical gradient installation; d) temperature t°C and weightinghumidity W X of frozen rocks; e) layouts of measuring resistivity logginginstallations.Comparison of the plots in Figure lb and ICsuggests that, in principle, the use of a middleThe example just considered reflects an insignificantfraction of work on the effectiveness ofgradient installation makes it possible to deter- resistivity logging methods. (See Akimov 1973,mine the transverse resistance of seams that form Bakulin 1967, Snegirev et al. 1980, 1981, andthe middle part of the cross section because within others).the borehole it helps create a vertical electrical In summarizing, the following has to be emphas-field, ensures the measurement of fairly highvalues of electrical potentials, and removes theinfluence of shielding effects on the measurementresults. Nevertheless, operations with this installationare complicated by the laborconsumingized. It is advisable to conduct studies of geoelectricalcross sections of frozen rocks withresistivity logging within boreholes driven withoutthe application of drilling fluids. The technicaland methodological problems can be overcome if theoperations needed to provide reliable grounding of factors that influence the accuracy of observationsthe feed electrode in the dry borehole shaft and and by distort logging plots are taken into considerathepresence within the borehole of a feed cable, tion and eliminated.which displaces the measuring dipole. ThereforeThe investigations carried out permit measurementthe vertical gradient installation for a study of of electrical field parameters within a dry boreholeshallow dry boreholes provides a number of advan- with a relative error of 1-3%; which makes ittages as compared to the known point resistivitylogging technique KC.The essence of these merits lies in the possipossibleto utilize logging installations in experimentsand observations of weak-gradient processesoccurring within permafrost.bility of obtaining plain-shaped plots of observa- The peculiarities of resistivity logging of rockstions, uncomplicated by shielding effects, that outlined above do not cover the diversity of factorspermit solution of a major logging problem, namely that researchers may encounter, but we feel they athe determination of the parameters of rock seamsthat have different composition and properties. Inaddition, it is also possible to run continuouscrucial. The degree of reliability in determiningthe electrical parameters of the cross section usingresistivity logging dara-will largely determine theresistivity logging of rocks within a dry borehole. successful application of electrical methods inNo attempts have been made to address this problem areas of development of permafrost. Therefore therethrough the use of three-electrode probes because is a need for further development of the techniquesof the extreme difficulty of producing a currentstabilizer that operates where there is sharpvariation of load. With the vertical gradientinstallation, the need for such a stabilizer nofor borehole investigations. An in-depth study andaccumulated experience will make it possible, takininto account the state-of-the-art of the measuringtechnique, to start implementation of the mostlonger arises, while the variation of the installa- advantageous continuous resistivity logging oftion coefficient as the measuring dipole moves along frozen rocks in dry boreholes.the borehole shaft can be compensated for.