AU2015202841A1 - Non-polarizable probe and spectral induced polarization logging device including the same - Google Patents

Abstract

A non-polarizable probe and a spectral induced polarization logging device for a borehole including the same are provided. The non-polarizable probe includes a main body 5 having an internal space, and a set of electrodes disposed in the main body. The electrodes include a current electrode to supply electric current to a target and a potential electrode to measure a potential induced from the target. The electrodes are spaced a predetermined distance from each other. Each of the electrodes includes an inner casing having an internal space, a lead rod wound around the inner casing, an outer casing covering the inner casing 10 wound with the lead rod, and a filling material filling the space between the outer casing and the inner casing. _200 100 12C1P1P21----------4 12 l P P213 411

Description

NON-POLARIZABLE PROBE AND SPECTRAL INDUCED POLARIZATION LOGGING DEVICE INCLUDING THE SAME 5 BACKGROUND 1. Technical Field The present invention relates to a non-polarizable probe and a spectral induced polarization logging device including the same. More particularly, present invention relates 10 to a non-polarizable probe that is inserted into a borehole and performs spectral induced polarization logging to allow rapid determination of distribution and characteristics of a metal ore body containing sulfide ores and a spectral induced polarization logging device for boreholes including the same. 15 2. Description of the Related Art A conventional induced polarization method is a method in which a polarization phenomenon is induced by application of electric current through the ground and measured to explore the underground structure. The induced polarization method includes two methods. (a) One of the methods is 20 a time-domain induced polarization method in which electric current is applied through the ground for a predetermined period of time and a charged state is then measured based on voltage between potential electrodes. (b) The other method is a frequency-domain induced polarization method in which apparent resistivity is measured using two or more ranges of frequencies (10 Hz or less) such that frequency effects, metal-related coefficients, and the 25 like are measured. Otherwise, after application of electric current for one second or more at a low frequency, a phase difference between measured potential and the phase of current is measured. In a spectral induced polarization method, an amplitude and phase of a spectral frequency are measured. This method can eliminate disadvantageous electromagnetic 30 coupling from the conventional induced polarization inspection, permit deep exploration 1 based on induced polarization data for a great quantity of frequencies, perform identification of the size, amount and kind of minerals, and remove a variety of artificial noise, membrane polarization, etc. In this method, the induced polarization data are mainly analyzed using a Cole-Cole model, which is used for estimating an oilfield reaction. 5 Generally, the exploration of spectral induced polarization is performed on the ground surface. However, in order to identify mineral ores and resource deposits, boring investigation has been generally carried out based on visual inspection by core logging. Thus, the analysis results differ depending upon observer's experience and knowledge. Precise evaluation of ore blocks is finally performed through laboratory observation and 10 analysis of sample pieces and compositions together with visual inspection. However, since this process takes much time, there is a need for a method of quickly evaluating ore blocks and their grades in the field. BRIEF SUMMARY 15 The present invention provides a non-polarizable probe that may be inserted into a borehole and performs spectral induced polarization logging to allow rapid determination of distribution and characteristics of a metal ore body containing sulfide ores, and a spectral induced polarization logging device for boreholes including the same. 20 In accordance with one aspect of the present invention, a non-polarizable probe includes: a main body having an internal space; and a set of electrodes disposed in the main body and spaced a predetermined distance from each other. The set of electrodes includes a current electrode and a potential electrode. Each of the electrodes includes: an inner casing having an internal space, a lead rod wound around the inner casing, an outer 25 casing covering the inner casing wound with the lead rod, and a filling material filling the space between the outer casing and the inner casing. The main body may be made of polyvinyl chloride (PVC). The lead rod may be made of lead and coated with lead chloride. The lead rod may be wound once around an outer surface of the inner casing and 30 the outer casing may be perforated to form a plurality of holes. 2 The filling material may be prepared by mixing lead chloride powder, sodium chloride and gypsum into a mixture, kneading the mixture while adding distilled water, and finally curing the mixture. The mixture of lead chloride powder, sodium chloride and gypsum may have a 5 mixing ratio of 50 to 58 : 30 to 38 : 10 to 18 in terms of % by weight. The set of electrodes may include a first current electrode and first and second potential electrodes. The first current electrode, the first potential electrode, and the second electrode are disposed in this order from a lower portion of the main body. The main body may be provided at upper and lower portions thereof with a circuit 10 board and a battery, respectively. The current electrode and the potential electrode may be disposed between the battery and the circuit board. The battery, the circuit board and the set of electrodes may be connected to each other by a cable. The inner casing and the outer casing may be made of polyvinyl chloride (PVC). Each of the electrodes may be formed with male screw sections at opposite sides 15 and may be screw-fastened to female screw sections of the main body. An 0-ring may be fitted into each of screw-fastened portions between the electrode and the main body. The main body may be coupled at an upper portion thereof to a waterproof pad for the main body, and a portion of the cable exposed from the main body may be covered by a cable sheath. 20 In accordance with another aspect of the present invention, a spectral induced polarization logging device for a borehole includes: the non-polarizable probe according to any one of the above features; a winch lifting or lowering the non-polarizable probe in a borehole using a cable; a measuring instrument connected to the winch via the cable and transmitting electric current and receiving a measured potential to perform induced 25 polarization inspection; and an additional electrode installed on the ground to supply electric current to the ground under control of the measuring instrument. BRIEF DESCRIPTION OF THE DRAWINGS 30 The above and other features and advantages of the present invention will become 3 apparent from the following description of exemplary embodiments given in conjunction with the accompanying drawings, in which: Fig. 1 is a view of a spectral induced polarization logging device for a borehole according to one exemplary embodiment of the present invention; 5 Fig. 2 is a cross-sectional view of a non-polarizable probe according to one exemplary embodiment of the present invention; Fig. 3 is a side sectional view of assembled electrodes of the non-polarizable probe according to the exemplary embodiment of the present invention; Fig. 4 is a side sectional view of the electrodes of the non-polarizable probe 10 according to the exemplary embodiment of the present invention; and Fig. 5 is a graph depicting logging results on spectral induced polarization and electric resistivity measured by a spectral induced polarization logging device for a borehole according to one exemplary embodiment of the present invention. 15 DETAILED DESCRIPTION Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Referring to Fig. 1, a spectral induced polarization logging device according to 20 one exemplary embodiment of the present invention is configured to perform logging of spectral induced polarization in a borehole. The logging device includes a probe 100 inserted into a borehole, a winch 200 that lifts or lowers the probe 100 using a cable, and a measuring instrument 300 that is connected to the winch 200 via the cable and transmits electric current and receives a measured potential. 25 The measuring instrument 300 includes a transmitter which transmits electric current, and a receiver which receives a measured potential. Here, the transmitter may transmit electric current in the range of 100pA to 100mA and at frequencies ranging from 10 1 Hz to 32MHz via a constant-current circuit. The receiver may receive a measured potential, whereby the measuring instrument 300 can spectrally measure an amplitude and 30 phase difference. 4 The winch 200 winds or unwinds a cable to lift or lower the probe 100, which is connected to the cable, in a borehole. The winch may unwind the cable up to a depth of 500 m that reaches the lowest depth of the borehole, where spectral induced polarization can be measured. Winding or unwinding of the cable is performed by an electric motor in 5 order to move the probe 100 within the borehole. The probe 100 may include a set of non-polarizable electrodes and is connected to the measuring instrument 300 via the cable. The probe 100 is one of the most important elements in logging spectral induced polarization. The probe is inserted into the borehole to perform induced polarization logging. The probe is waterproof to resist water pressure at 10 500 m or more. A detailed construction of the probe is shown in Fig. 2. Referring to Fig. 2, the probe 100 includes a waterproof main body 11, a battery 12 at the lower portion of the main body 11, a circuit board 13 at an upper portion of the main body 11, and a set of electrodes Cl, P1, P2. Here, the battery 12, the circuit board 13, and the electrodes are connected to each other by the cable. 15 The main body 11 is formed of a cylindrical pipe which encapsulates the battery 12, the circuit board 13 and the electrodes Cl, P1, P2 . The main body may be made of a non-conductive material. Preferably, the main body may be comprised of a polyvinyl chloride (PVC) pipe having a diameter of about 47 mm. The battery 12 supplies charging power to the electrodes. Specifically, the battery 20 12 may supply operation power to the first and second potential electrodes P1, P2 and supply power to the circuit board 13 to amplify a measured signal. The battery 12, having high capacity, may supply charging power to a first current electrode C1 to allow measuring current to flow around the borehole, supply operation power to the first and second potential electrodes P1, P2, and supply amplification power to the circuit board 13. 25 Thus, spectral induced polarization logging may be performed using the battery 12 without separately applying external power to the probe 100. The circuit board 13 may include an amplification circuit, which amplifies a potential measured by the first and second potential electrodes P1, P2 and outputs the measured potential to the measuring instrument 300. 30 The main body 11 is coupled at an upper portion thereof to a waterproof pad 14 5 for waterproofing of the main body 11. A portion of the cable exposed from the main body is covered by a cable sheath 15. The electrodes are arranged such that the first current electrode C1, the first potential electrode P1 and the second potential electrode P2 are disposed in the named 5 order between the battery 12 and the circuit board 13. Further, a second current electrode C2 (not shown) may be placed on the ground. Here, the respective electrodes may be spaced at regular intervals of about 300 mm within the main body 11. With such an arrangement of the electrodes, the first current electrode C1 is inserted into and moved along the borehole while being received in the probe 100. The 10 second current electrode C2 is placed on the ground, thereby allowing a wider range of induced polarization logging. Here, the first and second current electrodes Cl, C2 are powered by an external power source via a cable, or otherwise by the battery 12, whereby these electrodes can supply the current around the borehole. Further, the first and second potential electrodes P1, P2 are inserted into and moved along the borehole while being 15 received in the probe 100. By facilitating identification of metal ore zones, the potential electrode can measure the induced polarization during moving. Referring to Fig. 3, the first current electrode Cl, the first potential electrode P1, and the second potential electrode P2 may include male screw sections on opposite sides and be screw-fastened to female screw sections of the main body 11. For waterproofing of 20 screw-fastened portions between the electrode and the main body, rubber O-rings 16 are fitted into screw-fastened portions between each of the electrodes C1 and C2 and the main body. The structure of the electrodes including the first current electrode Cl, the first potential electrode P1, and the second potential electrode P2 will now be described in more 25 detail with reference to Fig. 4. The electrodes Cl, P1, P2 are non-polarizable electrodes, through which electricity can flow through charge movement on an interface between the electrode and an electrolyte. In the art, however, a polarizable electrode, such as a copper pipe, is used as an electrode. With the copper pipe, normal current flow is hindered because positive ions in 30 the electrolyte gather around the negative electrode and negative ions in the electrolyte 6 gather around the positive electrode. In actual measurement of induced polarization, the current electrode first supplies electric current towards a mineral ore body containing sulfide ores for a certain period of time (e.g. one second) and stops supplying of electric current to induce polarization from 5 the mineral ore body. Then, the potential electrode measures the induced polarization from the mineral ore body. However, for the copper pipe used as an electrode, polarization occurs at the electrode, inducing noise in the polarizing signal from the mineral ore body. In this embodiment, the electrode Cl, P1 or P2 includes an inner casing 21, which has an internal space. A lead rod 22 winds around the inner casing 21. An outer casing 24 10 surrounds the inner casing 21, which is wound with the lead rod 22. A filling material 23 fills the space between the outer casing 24 and the inner casing 21. The lead rod 22 is connected to the cable. The inner casing 21 may be formed of a hollow polyvinyl chloride (PVC) pipe. The lead rod 22 may be formed of an elongated lead (Pb) rod, which may be 15 coated with lead chloride (PbCl 2 ). Specifically, the lead rod 22 may be coated with lead chloride (PbCl 2 ) via electrolysis. During manufacture of the lead rod 22, the lead rod may be coated with lead chloride by other coating methods instead of electrolysis. The lead rod 22 is wound once around the outer surface of the inner casing 21. With the wound structure of the lead rod 22, the electrodes (Cl, P1, P2) may perform 20 induced polarization logging in all horizontal directions (360 ) while moving up or down along the borehole. The filling material 23, which fills the space between the outer casing 24 and the inner casing 21 wound with the lead rod 22, may be prepared by mixing gypsum (CaSO 4 2H 2 0), which is prepared by mixing lead chloride (PbCl 2 ) powders and sodium 25 chloride (NaCl) with distilled water to form a filling material paste. The prepared paste is poured into the space inside the outer casing 24 and then cured. The filling material paste filling the outer casing 24 may be prepared by mixing lead chloride (PbCl 2 ) powder, sodium chloride (NaCl), and gypsum (CaSO 4 2H 2 0) in a mixing ratio of 50 to 58wt%: 30 to 38wt%: 10 to 18wt%. The preferable mixing ratio is 30 54wt%: 34wt%: 12wt% and the mixture can be kneaded while adding distilled water and 7 curing the mixture. The outer casing 24 is wholly perforated to form a plurality of holes 25. The perforated holes 25 allow the electrodes Cl, P1 and P2 to perform induced polarization logging in every direction around the borehole, i.e. in all horizontal directions (360 ) in 5 the borehole, while the electrodes move up or down along the borehole. Next, a method of manufacturing such a non-polarizable electrode will be described. First, an inner casing 21, a lead rod 22 coated with lead chloride, an outer casing 24 that has holes formed over the whole surface, and a filling material are prepared. The lead rod 22 is wound once (3600 ) and fixed around the outer surface of the inner casing 10 21. The outer casing 24 is then placed around the inner casing. A mixture of lead chloride (PbCl 2 ) powder, sodium chloride (NaCl) and gypsum (CaSO 4 2H 2 0) in a mixing ratio described above fills the inside of the outer casing 24. The mixture is blended with distilled water into a paste while slowly adding distilled water, thereby completely filling the inner space of the outer casing 24. The paste is then dried in the shade for about 3 days. 15 Example Induced polarization logging was performed in a tunnel of Gagok mine in Samchuck, Korea using a spectral induced polarization logging device. This invention was used to check the possibility of evaluating characteristics of a mineral ore body. 20 Gagok mine has the geological features in which granite gneiss is distributed as underlying rock. Jangsan quartzite layers, Myobong slate layers, Pungchon limestone layers, Hwajeol layers, Dongjum quartzite layers are distributed to match with each other over the underlying rock. Ores in Gagok mine generally include galena and sphalerite in which limestone in Punchon limestone and Myobong slate layers are formed as contact 25 metasomatic deposits. A target borehole was a borehole No. 11-2 in the tunnel of Gagok mine to perform spectral induced polarization inspection. The depth of borehole No. 11-2 was 400 m. As a result of induced polarization inspection, a mineralized zone was found at 330 to 340 m; slate layers were found at other 30 sections. Fig. 5 shows the logging results on spectral induced polarization and electric 8 resistivity. The spectral induced polarization logging was measured in a frequency range of 0.125 to 16 Hz, and the measured result was compared with a resistivity-test result in order to verify the measured result. As a result of resistivity-test of Fig. 5, the resistivity at an ore-distributed section 5 was lower than the other sections of the slate layers, since the ore-distributed section contains sulfide ores that have high electric conductivity relative to the slate layers. It could be found that the region with low resistivity means a mineralized zone, and thus large phase difference in the induced polarization occurs in that region. Thus, as a result of induced polarization-testing, variation in phase was distinct in a mineralized zone, which 10 facilitates determination of the location of metal ore deposits containing sulfide ores. The non-polarizable probe of this invention configured to be effective in inspection of a metal ore body containing sulfide ores is inserted into a borehole and performs spectral induced polarization logging, thereby enabling rapid determination of distribution and characteristics of the metal ore body containing sulfide ores. 15 In addition, polarization is generated between the electrodes of the probe to prevent a polarization signal induced from a mineral ore body from becoming noise. As a result the potential electrodes can precisely measure polarization induced from the mineral ore body containing sulfide ores. Furthermore, the probe includes a lead rod wound around the electrode and the 20 perforated outer PVC cover, thereby enabling measurement of induced polarization in any directions in the borehole. Although some exemplary embodiments have been disclosed with reference to the accompanying drawings, it should be understood that these embodiments are provided for the purpose of illustration only and are not intended to limit the scope of the invention set 25 forth in the appended claims. Therefore, it will be apparent to those skilled in the art that various modifications, changes, and alterations can be made without departing from the spirit and scope of the invention. The scope of the invention should be limited only by the accompanying claims and equivalents thereof. 9

Claims (12)

1. A non-polarizable probe comprising: a main body having an internal space; and 5 a set of electrodes disposed in the main body and spaced a predetermined distance from each other, the set of electrodes comprising a current electrode and a potential electrode; each of the electrodes comprising: an inner casing having an internal space; 10 a lead rod wound around the inner casing; an outer casing covering the inner casing wound with the lead rod; and a filling material filling the space between the outer casing and the inner casing.

2. The non-polarizable probe according to claim 1, wherein the main body is made 15 of polyvinyl chloride (PVC).

3. The non-polarizable probe according to claim 1, wherein the lead rod is made of lead and coated with lead chloride. 20

4. The non-polarizable probe according to claim 1, wherein the lead rod is wound once around an outer surface of the inner casing and the outer casing is perforated to form a plurality of holes.

5. The non-polarizable probe according to claim 1, wherein the filling material is 25 prepared by mixing lead chloride powder, sodium chloride and gypsum into a mixture, kneading the mixture while adding distilled water, and finally curing the mixture.

6. The non-polarizable probe according to claim 5, wherein the mixture of lead chloride powder, sodium chloride and gypsum has a mixing ratio of 50 to 58 : 30 to 38 : 10 30 to 18 in terms of % by weight. 10

7. The non-polarizable probe according to claim 1, wherein the set of electrodes comprises a first current electrode and first and second potential electrodes, the first current electrode, the first potential electrode, and the second electrode being disposed in this order 5 from a lower portion of the main body.

8. The non-polarizable probe according to claim 1, wherein the main body is provided at upper and lower portions thereof with a circuit board and a battery, respectively, the current electrode and the potential electrode are disposed between the battery and the 10 circuit board, and the battery, the circuit board and the set of electrodes are connected to each other by a cable.

9. The non-polarizable probe according to claim 1, wherein the inner casing and the outer casing are made of polyvinyl chloride (PVC). 15

10. The non-polarizable probe according to claim 1, wherein each of the electrodes is formed with male screw sections at opposite sides thereof and is screw-fastened to female screw sections of the main body, and an O-ring is fitted into each of screw-fastened portions between the electrode and the main body. 20

11. The non-polarizable probe according to claim 1, wherein the main body is coupled at an upper portion thereof to a waterproofing pad for the main body, and a portion of the cable exposed from the main body is covered by a cable sheath. 25

12. A spectral induced polarization logging device for a borehole comprising: the non-polarizable probe according to any one of claims 1 to 11; a winch lifting or lowering the non-polarizable probe in a borehole using a cable; a measuring instrument connected to the winch via the cable and transmitting electric current and receiving a measured potential to perform induced polarization 30 inspection; and 11 an additional electrode installed on the ground so as to supply electric current to the ground under control of the measuring instrument. 12