RU2402047C1 - Measurement procedure at lateral logging of wells - Google Patents

Abstract

FIELD: oil and gas production. ^ SUBSTANCE: alternate feed current is supplied to electrically connected central and shield electrodes of arrangement. Current I0 of the central electrode and potential öU of screen electrodes are measured relative to a reference electrode. During logging there are also measured specific resistance üc of drilling fluid and temperature t in the well. There is determined resistance of r0t circuit connecting central and shield electrodes at temperature t out of ratio: r0t=r0(1+öt), where r0 is resistance of the circuit preliminary measured at 20C; öt=t-20; and is a temperature coefficient of resistance. Further, there is calculated ratio and is determined apparent resistivity ük of rock from preliminary calculated dependencies for a row of values of specific resistance of a formation, of resistance r0 and nominal diametre of the well. ^ EFFECT: upgraded accuracy of measurements and reliability of their execution, automatic record of well influence. ^ 1 dwg

Description

The invention relates to geophysical methods for studying sections of oil and gas wells and, in particular, to three-element lateral logging, designed to measure the apparent resistivities of rocks.

где k - коэффициент зонда. При этом низкоомный шунт реализуют с помощью входного трансформатора тока центрального электрода и резистора, включенного параллельно его вторичной обмотке.A known method of measurement in lateral logging with a three-electrode probe (see, for example, S. S. Itenberg, T. D. Dakhkilgov. Geophysical surveys in wells. M .: "Nedra", 1982. S. 108, 131, 132), with where an alternating current is supplied to the central and shield electrodes of the probe, interconnected to equalize their potentials with an electric shunt of small (≈0.01 Ohm) resistance, the current I _{0 of the} central electrode and the potential ΔU of the shield electrodes relative to the reference electrode are measured and the apparent specific resistance ρ of _a mountain od from the relation:

where k is the coefficient of the probe. In this case, a low-impedance shunt is realized using an input current transformer of the central electrode and a resistor connected in parallel with its secondary winding.

This measurement method gives satisfactory results at not too low resistivities (> 0.1 Ohm · m) of the drilling fluid.

However, the potential equalization is carried out with some approximation, and there is a small potential difference between the central and screen electrodes of the probe, which distorts the probe field and ultimately introduces an error in the measurement results, the greater the lower the resistivity of the drilling fluid filling the well. In this case, the measurement error can reach 100% (see V.T. Chukin et al. On the effect of the potential inequality of the probe electrodes on the results of three-electrode lateral logging. In Sat: “Applied Geophysics.” Issue 39, M .: “Nedra” , 1964. S.114-122).

The distortion of the probe field caused by the inequality of potentials and the associated measurement error lead to a violation of the constancy of the probe coefficient in expression (1).

There is a known measurement method (see AG Melnikov. On the issue of equalizing the potentials of electrodes in lateral logging tools of the BK-3 type. NTV “Logger”. 2004. Issue 8 (121). S.51-53), in which potential equalization The probe electrodes are produced using an operational amplifier, the inputs of which are connected to the secondary winding of the input current transformer of the central electrode. A supply alternating current is supplied to the electrode system, the current of the central electrode and the potential of the screen electrodes relative to the reference electrode are measured, and the apparent resistivity of the rocks is determined from relation (1).

In this measurement method, the reduced resistance between the probe electrodes is reduced to 0.0035 Ohms, which increases the accuracy of the measurements.

However, such results are achieved when the input current transformer of the central electrode is located in close proximity to the central and shield electrodes of the probe, and the resistance of the connecting wires can be neglected. This is not always possible. So, in the side logging equipment used for measurements during well drilling, the central and screen electrodes of the probe are located on the outer surface of the drill pipe and are connected to the measuring electronic unit by conductors of considerable length (up to 2 m) (see, for example, A.A. Molchanov . Measurement of geophysical and technological parameters in the process of drilling wells. M .: "Nedra". 1983. S. 52-57).

The widespread use of polymer-salt drilling fluids with resistivities up to 0.02 Ohm · m while drilling wells exacerbate this situation. In addition, the resistance of the conductors depends on the temperature in the well, which introduces an additional temperature error in the measurement results.

There is also a method of measurement (See Melnikov A. G. On the issue of equalizing the potentials of electrodes in lateral logging tools of the BK-3 type. NTV “Logging”. 2004. Issue 8 (121). C51-53), adopted as a prototype, in in which the potential equalization of the probe electrodes is carried out using an operational amplifier, the inputs of which are connected directly to the central and screen electrodes of the probe. A supply alternating current is supplied to the electrode system, the current I _{0 of the} central electrode and its potential ΔU relative to the reference electrode are measured and the apparent resistivity of the rocks is determined from the relation:

The use of a transformerless potential equalization circuit in this method eliminates the influence of connecting conductors and temperature changes in their resistances on the measurement results.

The disadvantage is the low stability of the operational amplifier in such a measurement scheme, which leads to its self-excitation and, accordingly, a sharp decrease in the accuracy of measurements or the general impossibility of their implementation.

The objectives of the present invention are to improve the accuracy of measurements and the reliability of their implementation.

по которому судят о кажущемся удельном сопротивлении ρ_к горных пород, дополнительно в процессе каротажа измеряют удельное сопротивление ρ_с бурового раствора и температуру t° в скважине, определяют сопротивление r_0t цепи, соединяющей центральный и экранный электроды, при температуре t° из соотношения: r_0t=r₀(1+α·Δt°), где r₀ - сопротивление цепи, предварительно измеренное при 20°С; Δt=t°-20°; α - температурный коэффициент сопротивления, после чего определяют ρ_k по предварительно рассчитанным зависимостям

для ряда значений удельного сопротивления пласта, сопротивления r₀ и номинального диаметра скважины.This is achieved by the fact that in the measurement method for lateral logging of wells, in which an alternating current is supplied to the central and screen electrodes of the probe, the current I _{0 of the} central electrode and the potential ΔU of the screen electrodes relative to the reference electrode are measured, and the ratio is calculated

according to which the apparent resistivity ρ _{to the} rocks is judged, in addition, during the logging process, the resistivity ρ _{from the} drilling fluid and the temperature t ° in the well are measured, the resistance r _{0t of the} circuit connecting the central and screen electrodes is determined at a temperature t ° from the relation: r _0t = r ₀ (1 + α · Δt °), where r ₀ is the circuit resistance previously measured at 20 ° С; Δt = t ° -20 °; α is the temperature coefficient of resistance, after which ρ _{k is} determined from the previously calculated dependencies

for a number of values of formation resistivity, resistance r ₀ and nominal well diameter.

Thus, in the proposed method, a strict equalization of the potentials of the probe electrodes is not necessary, since the influence of the potential inequality is taken into account in the calculated dependences, and the probe coefficient due to its variability in this case is not used to determine ρ _k .

This reduces the requirements for the current measuring circuit of the central electrode, which can be used as a traditional transformer circuit and can be used quite long connecting wires.

могут быть получены в результате математического моделирования методом интегральных уравнений (см., например, Р.А.Кучеров. К расчету поля зондов бокового каротажа в пластах ограниченной мощности при наличии скважины. Известия высших учебных заведений. Геология и разведка. 1980. №7. С.93-96).Estimated Dependencies

can be obtained as a result of mathematical modeling by the method of integral equations (see, for example, R.A. Kucherov. On calculating the field of lateral logging probes in formations of limited power in the presence of a well. News of higher educational institutions. Geology and exploration. 1980. No. 7. S.93-96).

рассчитанных для удельных сопротивлений ρ_n пластов от 0,25 до 4096 Ом·м, r₀=0,25 Ом и диаметра d_k скважины 0,125 м.The drawing shows an example of dependencies

calculated for the resistivities ρ _{n of the} formations from 0.25 to 4096 Ohm · m, r ₀ = 0.25 Ohm and the diameter d _{k of the} well 0.125 m

и номинальный диаметр скважины.The method is as follows. The borehole logging equipment is additionally equipped with a resistivimeter and a thermometer, and the ground part is supplemented with a computerized computing unit, in the memory of which a previously measured resistance value r _{0 of the} circuit connecting the central and screen electrodes is entered, the previously calculated dependencies

and nominal well diameter.

и сопротивление r_0t. Исходя из значений r_0t и d_н, из памяти вычислительного блока извлекают соответствующую им зависимость

по которой, используя измеренные значения отношения

и удельного сопротивления ρ_с, определяют кажущееся удельное сопротивление ρ_k горных пород. При необходимости при выборе зависимости

и определении ρ_k используют линейную интерполяцию.In the logging process, the current I _{0 of the} central electrode, the potential ΔU of the screen electrodes relative to the reference electrode, the resistivity ρ _{s of the} drilling fluid and temperature t ° are measured. The measurement results are sent to the computing unit, with which the ratio is calculated

and resistance r _0t . Based on the values of r _0t and d _n from the memory of the computing unit, the corresponding dependence is extracted

according to which, using measured values of the ratio

and resistivity ρ _s , the apparent resistivity ρ _k of the rocks is determined. If necessary, when choosing a dependency

and the definition of ρ _k using linear interpolation.

The value of the temperature coefficient α for a particular metal of conductors is selected from reference data or determined experimentally. So for copper conductors α = 0.0039 deg ^-1 .

The proposed method allows to increase the accuracy of the measurement of apparent resistivities and the reliability of their implementation.

рассчитаны для условий пласта, пересеченного скважиной. Так, в непроницаемых пластах кажущееся сопротивление ρ_k, определенное по данному способу, будет соответствовать удельному сопротивлению ρ_n пласта.In addition, in this method, the effect of the well on the measurement results is automatically taken into account, since the dependencies

calculated for the conditions of the reservoir crossed by the well. So, in impermeable formations, the apparent resistance ρ _k determined by this method will correspond to the resistivity ρ _{n of the} formation.

Claims (1)

A measurement method for lateral logging of wells, in which an alternating current is supplied to the central and screen electrodes of the probe, the current I _{0 of the} central electrode and the potential ΔU of the screen electrodes relative to the reference electrode are measured, and the ratio

according to which the apparent resistivity of the rocks is judged, characterized in that, in addition to the logging process, the resistivity ρ _{c of the} drilling fluid and the temperature t ° in the well are measured, the resistance r _{0t of the} circuit connecting the central and screen electrodes is determined at a temperature t ° of ratios: r _0t = r ₀ (1 + α · Δt °), where r ₀ - circuit resistance, previously measured at 20 ° C; Δt = t ° -20 °; α is the temperature coefficient of resistance, after which ρ _{k is} determined from the previously calculated dependencies

for a number of values of formation resistivity, resistance r ₀ and nominal well diameter.