CN113640583B - Spiral ring type core resistivity measuring device and method - Google Patents
Spiral ring type core resistivity measuring device and method Download PDFInfo
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- CN113640583B CN113640583B CN202110997474.8A CN202110997474A CN113640583B CN 113640583 B CN113640583 B CN 113640583B CN 202110997474 A CN202110997474 A CN 202110997474A CN 113640583 B CN113640583 B CN 113640583B
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- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/08—Measuring resistance by measuring both voltage and current
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Abstract
The invention discloses a spiral ring type core resistivity measuring device and method, relating to the technical field of core resistivity measurement and comprising the following specific steps: the two electrodes are opposite without loading a rock core; applying alternating voltage with fixed amplitude and fixed frequency on the transmitting spiral ring, and measuring the induction voltage of the receiving spiral ring; calculating the background resistance value of the loop by using the alternating voltage and the induction voltage; loading a rock core between the two electrodes, applying a second alternating voltage with fixed amplitude and fixed frequency on the transmitting spiral ring, and measuring a second induced voltage of the receiving spiral ring; calculating the resistance value of a loop when the rock core is loaded by using the second alternating voltage and the second induction voltage; and (4) making a difference between the loop resistance value and the loop background resistance value, and calculating the resistivity of the rock core by using the size parameter of the rock core. In the invention, the measurement system and the rock core current path are independent, the error introduced by the additional impedance is small, stable and controllable, and the measurement result is accurate.
Description
Technical Field
The invention relates to the technical field of core resistivity measurement, in particular to a spiral ring type core resistivity measurement device and method.
Background
In the evaluation of oil and gas resource reservoirs, in order to know the relation between the resistivity characteristics of the reservoirs and the parameters of the reservoirs, a large number of petrophysical experiments are required to measure the resistivity of rocks. Rock resistivity measurement under variable saturation conditions is the most basic rock resistivity experiment, and liquid in a rock core needs to be displaced in the experiment process to change the properties in the pore structure of the rock core.
Traditional rock resistivity measurements are dominated by electrode and coil measurements. The electrode method measurement principle is voltammetry measurement, the resistance of the rock core is calculated by measuring the voltage and current applied to two ends of the rock core and utilizing ohm's law, and then the resistivity is calculated. Because the voltage and current signal acquisition system can enter a current path where the rock core is located, especially when the measurement system is aged, the internal resistance is difficult to estimate, and therefore the internal resistance of the measurement system and the signal excitation source can cause errors on the measurement result. The coil method is based on the electromagnetic induction principle for measurement, the structure of a measurement system is complex, and a complex circuit system needs to be designed under the low-frequency condition to inhibit direct coupling signals between coils. In addition, the core is not directly contacted, the measurement result reflects the local resistivity information of the core, and in a two-phase displacement experiment, due to the non-uniformity of oil-water distribution, the measurement result cannot reflect accurate core information, and in addition, the coil method has the following defects: the coil needs to be placed inside the core sample, and the sample needs to be damaged.
In the prior art, the measurement error of the core resistivity is large, and the core information cannot be accurately reflected, so that how to provide a brand-new, simpler and more accurate core resistivity measurement method is a problem to be urgently solved for a person skilled in the art.
Disclosure of Invention
In view of the above, the invention provides a spiral-wound ring type core resistivity measuring device and method, wherein a measuring system and a core current path are independent from each other, the error introduced by the additional impedance is small, stable and controllable, and the measuring result is accurate.
In order to achieve the purpose, the invention adopts the following technical scheme: on the one hand, the spiral wound ring type core resistivity measuring method is provided, and the specific steps comprise the following steps:
the two electrodes are opposite without loading a rock core;
applying alternating voltage with fixed amplitude and fixed frequency on the transmitting spiral ring, and measuring the induced voltage of the receiving spiral ring;
calculating a loop background resistance value by using the alternating voltage and the induction voltage;
loading a rock core between the two electrodes, applying a second alternating voltage with fixed amplitude and fixed frequency on the transmitting spiral ring, and measuring a second induced voltage of the receiving spiral ring;
calculating the resistance value of a loop when the rock core is loaded by using the second alternating voltage and the second induction voltage;
and calculating the resistivity of the rock core by using the size parameter of the rock core according to the difference between the resistance value of the loop and the background resistance value of the loop.
By adopting the technical scheme, the method has the following beneficial technical effects: the measuring system and the rock core current path are independent, the error introduced by the additional impedance is small, stable and controllable, and the measuring result is accurate. The signal intensity is related to the number of turns of the spiral winding ring, so that small signals can be conveniently amplified, and the measurement accuracy is improved.
Preferably, the formula for calculating the loop background resistance value is as follows:
wherein, K A Is the system scale factor, U in Is an alternating voltage, U out Is an induced voltage.
Preferably, the calculation formula of the induced voltage is as follows:
U out ＝K·I；
wherein K is an instrument coefficient and is a constant; i is the loop current.
Preferably, the calculation formula of the loop resistance value is the same as the calculation formula of the loop background resistance value.
On the other hand, the spiral-wound-ring-type core resistivity measuring device comprises a power supply, a transmitting spiral-wound ring, a receiving spiral-wound ring, a voltage detecting device and a core to be measured; the wire sequentially passes through the centers of the transmitting spiral ring and the receiving spiral ring; the voltage detection device is connected with the receiving spiral ring and used for measuring the induction voltage of the receiving spiral ring.
Preferably, the transmitting spiral winding ring and the receiving spiral winding ring are made of zinc-manganese ferrite, and the winding wire is an enameled copper wire.
Preferably, during the measurement, hydraulic oil with fixed pressure is injected into the hydraulic oil bin through a hydraulic oil pump.
By adopting the technical scheme, the method has the following beneficial technical effects: the liquid oil pump is used for providing confining pressure for the rock core sample and simulating an underground high-pressure environment, hydraulic oil with certain pressure is injected into the hydraulic oil bin through the hydraulic oil pump in the measuring process, and the rubber sleeve is tightly attached to the side faces of the rock core and the electrode, so that the measuring accuracy is guaranteed to be influenced due to the fact that no liquid space is shunted outside the rock core.
Preferably, the displacement fluid channel is pumped with a advection pump to inject fluid for displacement experiments during the measurement.
By adopting the technical scheme, the method has the following beneficial technical effects: the resistivity of the core under different oil saturation conditions can be measured.
According to the technical scheme, compared with the prior art, the spiral-wound ring type core resistivity measuring device and method are provided, the two end faces of the core are connected through the known lead with small resistance to form a current loop, and the loop penetrates through two spiral-wound rings (a transmitting spiral-wound ring and a receiving spiral-wound ring) with known turns. The method comprises the steps that low-frequency alternating voltage is applied to a transmitting spiral ring, direct current is generated in a core passage, the current is inversely proportional to loop resistance, low-frequency alternating voltage is induced on a receiving spiral ring, the voltage is related to the current in the core passage, the voltage of the receiving spiral ring is measured, the current of the core passage can be calculated, the resistance of the core passage is calculated, and the resistivity of the core is calculated. In the prior art, the core impedance is measured, a measuring system is connected with a core current path in series, and the internal impedance of the measuring system influences the measuring result. When the system ages or performance changes occur, the internal resistance changes nondeterministically, and errors which cannot be estimated are caused to the measurement result. By adopting the technical scheme of the invention, the measuring system and the rock core current path are independent, the error introduced by the additional impedance is small, stable and controllable, and the measuring result is more accurate. The signal intensity is related to the number of turns of the spiral winding ring, so that small signals can be conveniently amplified, and the measurement accuracy is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a schematic view of a spiral ring structure according to the present invention;
FIG. 3 is a flow chart of a method of the present invention;
FIG. 4 is a schematic diagram of a feasibility test circuit according to the present invention;
FIG. 5 is a graphical representation of the results of the feasibility test of the present invention;
wherein, 1 is a power supply, 2 is a transmitting spiral ring, 3 is a receiving spiral ring, 4 is a core to be measured, 5 is a hydraulic oil bin, 6 is a rubber sleeve, 7 is a displacement fluid channel, 8 is an electrode, 9 is a holder shell, 10 is a voltage detection device, 11 is a hydraulic oil pump, and 12 is a variable resistance box.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
The embodiment of the invention discloses a spiral-wound ring type core resistivity measuring device on one hand, and as shown in figure 1, the spiral-wound ring type core resistivity measuring device comprises a power supply 1, a transmitting spiral-wound ring 2, a receiving spiral-wound ring 3, a voltage detecting device 10 and a core 4 to be detected; the lead sequentially passes through the centers of the transmitting spiral ring 2 and the receiving spiral ring 3; and is connected in series with the core 4 to be measured to form a closed loop, the power supply 1 is connected with the transmitting spiral ring 2 and used for providing low-frequency alternating voltage, and the voltage detection device 10 is connected with the receiving spiral ring 3 and used for measuring the induction voltage of the receiving spiral ring 3. The structure of the spiral ring is shown in fig. 2.
In the measuring process, hydraulic oil with certain pressure is injected into the hydraulic oil bin 5 through the hydraulic oil pump 11, so that the rubber sleeve 6 is tightly attached to the side faces of the core 4 to be measured and the electrode 8, and the measuring accuracy is guaranteed to be affected due to the fact that no liquid space is shunted outside the core 4 to be measured. The displacement experiment can be carried out in the measuring process by injecting liquid into the displacement liquid channel 7 by using a constant-current pump, and the resistivity of the rock core under different oil saturation conditions can be measured.
On the other hand, a spiral wound ring type core resistivity measurement method is disclosed, as shown in fig. 3, the specific steps include the following:
the two electrodes are opposite without loading a rock core;
applying alternating voltage with fixed amplitude and fixed frequency on the transmitting spiral ring, and measuring the induction voltage of the receiving spiral ring;
calculating a loop background resistance value by using the alternating voltage and the induction voltage;
loading a rock core between the two electrodes, applying a second alternating voltage with fixed amplitude and fixed frequency on the transmitting spiral ring, and measuring a second induced voltage of the receiving spiral ring;
calculating the resistance value of a loop when the rock core is loaded by using a second alternating voltage and the second induction voltage;
and (4) making a difference between the loop resistance value and the loop background resistance value, and calculating the resistivity of the rock core by using the size parameter of the rock core.
Specifically, when an alternating voltage (U) is applied to the winding of the transmitting toroid in ) Then, a unidirectional annular magnetic field is generated in the magnetic ring, and the annular magnetic field induces a potential difference (U) at the two ends of the spiral ring again X ) When a closed loop in the magnetic ring is communicated, current passes through the loop (I). The voltage relationship between the toroid winding and the closed loop can be equivalent to a multi-turn to single-turn transformer. Thus, the following relationship exists:
in the formula, N is the number of turns of the transmitting spiral ring, and R is the total resistance of a current loop where the core is located.
When current passes through the center of the receiving spiral ring, a circular magnetic field is induced in the magnetic core, and an alternating voltage (U) is induced on the winding by the circular magnetic field out ). There is a linear relationship between the alternating voltage and the center conductor current, which can be expressed as:
U out ＝K·I (2)
k is the instrument coefficient, related to the number of turns of the receiving spiral winding wire, the material of the magnetic core and the like, unrelated to the loop resistance, and is a constant, and I is the loop current.
Combining the above two sets of relationships can yield:
in the formula K A The system scale factor shows that the resistance of the loop in which the core is located is in direct proportion to the ratio of the input voltage to the output voltage, so that the resistance of the loop in which the core is located can be calculated by determining the amplitude of the input voltage under the condition that the input voltage is known. In addition, the number of turns of the transmitting spiral ring and the receiving spiral ring is changed, the system proportionality coefficient can be adjusted, small signals are amplified and checked, and the measurement accuracy is improved.
In this embodiment, a feasibility test is performed on the method of the present invention, as shown in fig. 4, specifically as follows:
two spiral winding rings are prepared, the magnetic core of each spiral winding ring is made of zinc-manganese ferrite, and the winding wire is an enameled copper wire. The number of turns of the transmitting toroid 2 is 10 turns, and the number of turns of the receiving toroid 3 is 110 turns. The wire is threaded through the centers of the two spiral loops in turn and is connected in series with the variable resistance box 12 to form a loop. A sinusoidal voltage signal with the frequency of 100kHz and the amplitude of 10V is applied to the transmitting spiral ring by a signal generator, and the induced voltage of the receiving spiral ring is observed and recorded by an oscilloscope. The resistance of the resistance box was varied to simulate cores of different resistivities, the measurement results are shown in FIG. 5, and there was good between the ratio of the input voltage to the output voltage amplitude and the resistance of the resistance boxGood linear relationship, fitting with a linear function, R 2 Up to 0.99. The loop resistance can be calculated in reverse by using the fitting relation, and the difference value between the loop resistance and the display resistance of the resistance box is not more than 2%. The measurement loop used for the test is not a dedicated device, the accuracy is poor, and the received signal is a manual reading value, which may be a main source of error. The results demonstrate the feasibility of the design concept of the present invention.
In the present specification, the embodiments are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (2)
1. A spiral ring type core resistivity measuring method is characterized by comprising the following specific steps:
applying alternating voltage with fixed amplitude and fixed frequency to the transmitting spiral ring without loading a rock core between the two electrodes, and measuring the induced voltage of the receiving spiral ring;
calculating a loop background resistance value by using the alternating voltage and the induction voltage;
loading a rock core between the two electrodes, applying a second alternating voltage with fixed amplitude and fixed frequency on the transmitting spiral ring, and measuring a second induced voltage of the receiving spiral ring;
calculating the resistance value of a loop when the rock core is loaded by using the second alternating voltage and the second induction voltage;
calculating the resistivity of the rock core by utilizing the size parameter of the rock core as the difference between the resistance value of the loop and the background resistance value of the loop;
the formula for calculating the background resistance value of the loop is as follows:
wherein, K A Is the system scale factor, U in Is an alternating voltage, U out Is an induced voltage;
the calculation formula of the loop resistance value is the same as that of the loop background resistance value.
2. The spiral wound ring type core resistivity measuring method as claimed in claim 1, wherein the calculation formula of the induced voltage is as follows:
U out ＝K·I；
wherein K is an instrument coefficient and is a constant; i is the loop current.
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