阅读说明：本技术 一种地层视电导率测量方法 (Stratum apparent conductivity measuring method ) 是由 刘晓博 王安玲 刘福平 于 2020-12-21 设计创作，主要内容包括：本说明书一个或多个实施例提供的一种地层视电导率测量方法,通过在地层内构件测井系统,发射线圈发射低频阶跃形电磁波,接收线圈接收二次感应电动势V-R,从而计算地层总视电导率σ-a,去除其中金属套管、水泥环以及水泥环外泥浆的影响后,获得地层视电导率σ-4,从而准确的测量了地层视电导率。(One or more embodiments of the present disclosure provide a method for measuring apparent conductivity of a formation by constructing a logging system in the formation, wherein a transmitter coil transmits a low-frequency step electromagnetic wave, and a receiver coil receives a secondary induced electromotive force V R To calculate the total apparent conductivity σ of the formation a Removing the influence of the metal casing, the cement sheath and the mud outside the cement sheath to obtain the apparent conductivity sigma of the stratum 4 Thereby accurately measuring the apparent conductivity of the stratum.)

1. A method of measuring apparent conductivity of a formation, comprising:

constructing a logging system in a stratum, wherein the logging system comprises a metal casing, a cement sheath is arranged outside the metal casing, and a transmitting coil and a receiving coil are respectively arranged in the metal casing from bottom to top;

introducing low-frequency alternating current to the transmitting coil so as to enable the transmitting coil to transmit low-frequency step-shaped electromagnetic waves;

the receiving coil receives secondary induced electromotive force V_R；

Based on the secondary induced electromotive force V_RCalculating total apparent conductivity sigma of stratum_a；

Removal of the total apparent conductivity σ of the formation_aInfluence of the inner metal casing, the cement sheath and the outer mud of the cement sheath to obtain the apparent conductivity sigma of the stratum₄。

2. The method of claim 1, wherein the transmitter coil and the receiver coil are concentrically disposed within the metal casing and are located on a centerline of the metal casing.

3. The method of claim 1, wherein said measuring is based on said secondary induced electromotive force V_RCalculating total apparent conductivity sigma of stratum_aThe calculation formula of (2) is as follows:

wherein σ_aIs the total apparent conductivity of the formation;

V_Rto receive the secondary induced electromotive force in the coil;

k is the coefficient of the electrode (k),

l is the distance between the transmitting coil and the receiving coil;

S₀is the area of the transmitting coil, S₀＝πa²；

a is the radius of the transmitting coil;

omega is the round frequency of the transmitting coil;

mu is the stratum magnetic permeability;

n_Rto receive the number of turns of the coil;

n_Tthe number of turns of the transmitting coil;

i is the current in the transmit coil.

4. The method of claim 3 for measuring apparent conductivity of a subterranean formationMethod, characterized in that said removal of the total apparent conductivity σ of the formation_aInfluence of the inner metal casing, the cement sheath and the outer mud of the cement sheath to obtain the apparent conductivity sigma of the stratum₄The method comprises the following steps:

by

Wherein: g (r, z) is called differential geometry factor,

σ₁is the electrical conductivity of the metal sleeve;

σ₂is the electrical conductivity of the cement sheath;

σ₃the conductivity of the mud outside the cement sheath;

σ₄apparent conductivity for the formation;

ρ_Rthe distance from any point in space to the center of the receiving coil;

ρ_Tthe distance from any point in space to the center of the transmitting coil;

G₁、G₂、G₃、G₄are all integral geometric factors;

can obtain the product

5. The method of claim 4, wherein the measurement of apparent conductivity of the earth formation is performed by

6. The method of claim 5, wherein the measurement of apparent conductivity of the earth formation is performed by

u→0；

G₄＝M-G₃。

7. The method of claim 6, wherein the frequency of the low frequency alternating current is 1-30 Hz.

Technical Field

One or more embodiments of the present disclosure relate to the field of formation apparent conductivity measurement technologies, and in particular, to a formation apparent conductivity measurement method.

Background

Evaluation of residual oil and dynamic monitoring of oil and gas reservoirs are important problems to be solved by logging in the middle and later stages of development of oil and gas fields.

The existing through-casing resistivity detection method mostly adopts contact type measurement, and has the limitations of long test time, high cost, poor test effect and the like when a casing is deformed or corroded, so that the through-casing well measurement has larger uncertainty.

The transient electromagnetic method mainly uses a step wave or pulse current field source as excitation, and measures the change characteristics of a secondary induction field caused by a stratum medium during the intermittence of a primary field, thereby realizing the measurement of stratum electrical parameters. In the method, due to the important influence of the metal casing, the original theory of the ground transient electromagnetic method is not suitable for the through casing logging of the transient electromagnetic method in the well, the research of the through casing resistivity logging by using the transient electromagnetic method is still in the initial research stage of the experiment at present, the through casing resistivity logging is only limited to the measurement of field distribution response, a through casing resistivity measurement and calculation method based on the transient electromagnetic method is not available, a practical specific apparent resistivity calculation formula is not available, and the influence of the high-conductivity metal casing with the strong shielding effect on the measurement result is not eliminated and corrected.

Disclosure of Invention

In view of this, an object of one or more embodiments of the present disclosure is to provide a method for measuring an apparent conductivity of a formation, which can eliminate the influence of a metal casing, a cement sheath, and mud, and accurately achieve the measurement of the apparent conductivity of the formation.

In view of the above, one or more embodiments of the present disclosure provide a method for measuring apparent conductivity of a formation, comprising:

constructing a logging system in a stratum, wherein the logging system comprises a metal casing, a cement sheath is arranged outside the metal casing, and a transmitting coil and a receiving coil are respectively arranged in the metal casing from bottom to top;

introducing low-frequency alternating current to the transmitting coil so as to enable the transmitting coil to transmit low-frequency step-shaped electromagnetic waves;

the receiving coil receives secondary induced electromotive force V_R；

Based on the secondary induced electromotive force V_RCalculating total apparent conductivity sigma of stratum_a；

Removal of the total apparent conductivity σ of the formation_aInfluence of the inner metal casing, the cement sheath and the outer mud of the cement sheath to obtain the apparent conductivity sigma of the stratum₄。

As an alternative embodiment, the transmitting coil and the receiving coil are concentrically arranged in the metal sleeve and are located on the central line of the metal sleeve.

As an optional implementation, the second-order-basedInduced electromotive force V_RCalculating total apparent conductivity sigma of stratum_aThe calculation formula of (2) is as follows:

wherein σ_aIs the total apparent conductivity of the formation;

V_Rto receive the secondary induced electromotive force in the coil;

k is the coefficient of the electrode (k),

l is the distance between the transmitting coil and the receiving coil;

S₀is the area of the transmitting coil, S₀＝πa²；

a is the radius of the transmitting coil;

omega is the round frequency of the transmitting coil;

mu is the stratum magnetic permeability;

n_Rto receive the number of turns of the coil;

n_Tthe number of turns of the transmitting coil;

i is the current in the transmit coil.

As an optional implementation mode, the total apparent conductivity sigma of the removed stratum_aInfluence of the inner metal casing, the cement sheath and the outer mud of the cement sheath to obtain the apparent conductivity sigma of the stratum₄The method comprises the following steps:

by

Wherein: g (r, z) is called differential geometry factor,

σ₁is the electrical conductivity of the metal sleeve;

σ₂is the electrical conductivity of the cement sheath;

σ₃the conductivity of the mud outside the cement sheath;

σ₄apparent conductivity for the formation;

ρ_Rthe distance from any point in space to the center of the receiving coil;

ρ_Tthe distance from any point in space to the center of the transmitting coil;

G₁、G₂、G₃、G₄are all integral geometric factors;

can obtain the product

As an alternative embodiment, the

As an alternative embodiment, the

G₄＝M-G₃。

As an alternative embodiment, the frequency of the low-frequency alternating current is 1-30 Hz.

From the above, it can be seen that one or more embodiments of the present disclosure provide a method for measuring apparent conductivity of a formation by constructing a logging system in the formation, wherein a transmitting coil transmits a low frequency step electromagnetic wave, and a receiving coil receives a secondary induced electromotive force V_RTo calculate the total apparent conductivity σ of the formation_aRemoving the influence of the metal casing, the cement sheath and the mud outside the cement sheath to obtain the apparent conductivity sigma of the stratum₄Thereby accurately measuring the apparent conductivity of the stratum.

Drawings

In order to more clearly illustrate one or more embodiments or prior art solutions of the present specification, the drawings that are needed in the description of the embodiments or prior art will be briefly described below, and it is obvious that the drawings in the following description are only one or more embodiments of the present specification, and that other drawings may be obtained by those skilled in the art without inventive effort from these drawings.

FIG. 1 is a logic diagram of one or more embodiments of the present description;

FIG. 2 is a schematic illustration of a logging system according to one or more embodiments of the present disclosure;

FIG. 3 is a schematic diagram of a coordinate system established based on a logging system in accordance with one or more embodiments of the present disclosure.

Detailed Description

To make the objects, technical solutions and advantages of the present disclosure more apparent, the present disclosure is further described in detail below with reference to specific embodiments.

In order to achieve the above object, an embodiment of the present invention provides a method for measuring apparent conductivity of a formation, including:

constructing a logging system in a stratum, wherein the logging system comprises a metal casing, a cement sheath is arranged outside the metal casing, and a transmitting coil and a receiving coil are respectively arranged in the metal casing from bottom to top;

introducing low-frequency alternating current to the transmitting coil so as to enable the transmitting coil to transmit low-frequency step-shaped electromagnetic waves;

the receiving coil receives secondary induced electromotive force V_R；

Based on the secondary induced electromotive force V_RCalculating total apparent conductivity sigma of stratum_a；

Removing total apparent electricity of stratumConductivity sigma_aInfluence of the inner metal casing, the cement sheath and the outer mud of the cement sheath to obtain the apparent conductivity sigma of the stratum₄。

In the invention, a logging system is constructed in a stratum, a transmitting coil transmits low-frequency step electromagnetic waves, and a receiving coil receives secondary induced electromotive force V_RTo calculate the total apparent conductivity σ of the formation_aRemoving the influence of the metal casing, the cement sheath and the mud outside the cement sheath to obtain the apparent conductivity sigma of the stratum₄Thereby accurately measuring the apparent conductivity of the stratum.

FIG. 1 illustrates a method of apparent conductivity measurement of a formation, comprising:

s10, constructing a logging system in the stratum, wherein the logging system comprises a metal casing, a cement sheath is arranged outside the metal casing, and a transmitting coil and a receiving coil are respectively arranged in the metal casing from bottom to top;

as an alternative embodiment, as shown in fig. 2, the transmitting coil and the receiving coil are concentrically arranged in the metal sleeve and located on the center line of the metal sleeve, where R denotes the receiving coil, T denotes the transmitting coil, a denotes the radius of the transmitting coil and the radius of the receiving coil, the radius of the transmitting coil is equal to the radius of the receiving coil, and L denotes the distance between the transmitting coil and the receiving coil.

S20, introducing low-frequency alternating current to the transmitting coil to enable the transmitting coil to transmit low-frequency step-shaped electromagnetic waves;

optionally, the frequency of the low-frequency alternating current is 1-30 Hz.

S30, the receiving coil receives the secondary induced electromotive force V_R；

S40, based on the secondary induced electromotive force V_RCalculating total apparent conductivity sigma of stratum_a；

Optionally, the voltage based on the secondary induced electromotive force V_RCalculating total apparent conductivity sigma of stratum_aThe calculation formula of (2) is as follows:

wherein σ_aIs the total apparent conductivity of the formation;

V_Rto receive the secondary induced electromotive force in the coil;

k is the coefficient of the electrode (k),

l is the distance between the transmitting coil and the receiving coil;

S₀is the area of the transmitting coil, S₀＝πa²；

a is the transmit coil radius (receive coil radius);

omega is the round frequency of the transmitting coil;

mu is the stratum magnetic permeability;

n_Rto receive the number of turns of the coil;

n_Tthe number of turns of the transmitting coil;

i is the current in the transmit coil.

S50, removing the total apparent conductivity sigma of the stratum_aInfluence of the inner metal casing, the cement sheath and the outer mud of the cement sheath to obtain the apparent conductivity sigma of the stratum₄。

Optionally, the total apparent conductivity σ of the removed formation_aInfluence of the inner metal casing, the cement sheath and the outer mud of the cement sheath to obtain the apparent conductivity sigma of the stratum₄The method comprises the following steps:

wherein: g (r, z) is called differential geometry factor,

σ₁is the electrical conductivity of the metal sleeve;

σ₂is the electrical conductivity of the cement sheath;

σ₃is mud outside the cement sheathThe electrical conductivity of (a);

σ₄apparent conductivity for the formation;

ρ_Rthe distance from any point in space to the center of the receiving coil;

ρ_Tthe distance from any point in space to the center of the transmitting coil;

G₁、G₂、G₃、G₄are all integral geometric factors;

wherein, the following formula (1) and formula (2) can be obtained:

integrating the differential geometric factor g (r, z) with r

Equation (4) is referred to as the longitudinal geometry factor. Let r be²X then has

R＝[r²+(z+L/2)²][r²+(z-L/2)²]，

＝r⁴+(2z²+L²/2)r²+(z²-L²/2)²＝x²+(2z²+L²/2)x+(z²-L²/4)²

Let α ═ z²-L²/4)²，β＝2z²+L²And/2, if epsilon is 1, then R is alpha + beta x + epsilon x²，Δ＝4αε-β²＝-4z²L²，

The longitudinal geometry factor can be expressed as

As shown in FIG. 3, 1 denotes a metal casing, 2 denotes a cement sheath, 3 denotes a slurry outside the cement sheath, 4 denotes a bottom layer, and r denotes₁Representing the distance, r, of the centre line of the transmitter coil and the receiver coil from the outer diameter of the metal sleeve₂Representing the distance, r, of the center line of the transmitter coil and the receiver coil from the outer diameter of the cement sheath₃Showing the spacing of the transmitter coil and receiver coil centerlines from the outer diameter of the mud outside the cement sheath.

According to the integral interval of the formula (2), the longitudinal geometric factor can be written into the form of the partition longitudinal geometric factor by using the formula (5), and r is set²＝x，r₁ ²＝x₁，r₂ ²＝x₂，r₃ ²＝x₃Then the partition longitudinal geometric factor is

WhereinAlso obtain longitudinal geometric factors of other intervals

Unfolding R in the longitudinal geometric factor

Where a is²＝(r²+L²/4)²，b²＝r²-L²/4，

Integrating g (z) with z to obtain integral geometric factor

Wherein, it is provided with

u is the lower limit of integration, u is not less than 0, F (alpha, gamma) is the first class of elliptic integration,when u → 0, α ═ pi,e (α, γ) is a second type of complete elliptic integral. In the formula (12), a singular point exists when u is equal to 0, and the value of u is appropriately selected when the numerical value is calculated.

Order to

Wherein

The integral geometry factor can be written in the form of an r-function, and equation (6-9) can be written in the form of an algebraic sum of the two-part integral results

In equations (14) and (15), the calculation result approaches the integration result of equation (1) as long as u → 0 is taken, and thus the partition integration geometric factor can be expressed as

G₄＝M-G₃ (19)

Wherein G is₁+G₂+G₃+G₄＝1。

The embodiment of the invention has the following characteristics:

(1) an analytic calculation formula expression of the stratum apparent conductivity is derived, the stratum apparent conductivity is directly calculated by utilizing the secondary induced electromotive force of the receiving coil, and the problem that a calculation method is not available in the transient electromagnetic method through casing conductivity logging is solved;

(2) the method for correcting the influence of the metal casing with the strong shielding effect on the measurement result of the stratum apparent conductivity is provided, the automatic correction of the measurement result of the stratum apparent conductivity of the metal casing, the cement sheath and the borehole mud logging response is realized, and the problem that the influence of the high-conductivity metal casing on the measurement result is not eliminated and corrected is solved;

(3) the analytic calculation result of the integral geometric factor is utilized, the calculation speed is high, the calculation and settlement result is accurate, the algorithm can be directly placed in a chip of an instrument receiving coil, the real-time calculation and output of the stratum apparent conductivity of the transient electromagnetic field method are realized by utilizing the secondary induced electromotive force of the receiving coil, and the measurement and data processing speed is greatly improved.

Due to G₁、G₂、G₃、G₄The calculation is analytically represented, the calculation speed is high, the calculation result is accurate, and then G can be obtained₁、G₂、G₃、G₄The calculation method is written into a program and arranged in a measuring instrument, and metal casing, cement sheath and borehole mud sigma are actually input according to the field during logging₁、σ₂、σ₃r₁、r₂、r₃Equal parameters, calculate G₁、G₂、G₃、G₄And then, the formula (3) is utilized to carry out logging influence correction on the measurement result by using the metal casing, the cement sheath and the borehole mud, so that the real-time measurement calculation and data processing of the apparent conductivity of the through casing logging stratum are realized, and an apparent resistivity logging curve is directly formed.

It is to be appreciated that the method can be performed by any apparatus, device, platform, cluster of devices having computing and processing capabilities.

It should be noted that the method of one or more embodiments of the present disclosure may be performed by a single device, such as a computer or server. The method of the embodiment can also be applied to a distributed scene and completed by the mutual cooperation of a plurality of devices. In such a distributed scenario, one of the devices may perform only one or more steps of the method of one or more embodiments of the present disclosure, and the devices may interact with each other to complete the method.

The foregoing description has been directed to specific embodiments of this disclosure. Other embodiments are within the scope of the following claims. In some cases, the actions or steps recited in the claims may be performed in a different order than in the embodiments and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In some embodiments, multitasking and parallel processing may also be possible or may be advantageous.

Those of ordinary skill in the art will understand that: the discussion of any embodiment above is meant to be exemplary only, and is not intended to intimate that the scope of the disclosure, including the claims, is limited to these examples; within the spirit of the present disclosure, features from the above embodiments or from different embodiments may also be combined, steps may be implemented in any order, and there are many other variations of different aspects of one or more embodiments of the present description as described above, which are not provided in detail for the sake of brevity.

It is intended that the one or more embodiments of the present specification embrace all such alternatives, modifications and variations as fall within the broad scope of the appended claims. Therefore, any omissions, modifications, substitutions, improvements, and the like that may be made without departing from the spirit and principles of one or more embodiments of the present disclosure are intended to be included within the scope of the present disclosure.