Gravity acceleration measurement apparatus and extraction method in a rotating state

Abstract

An apparatus for measuring gravity acceleration of a drilling tool comprises sensors and a measurement circuit. The sensor comprises a three-axis gravity accelerometer, a reference measurement sensor and a temperature sensor. The three-axis gravity accelerometer measures acceleration component signals in three mutually orthogonal directions, and the reference measurement sensor generates a signal that varies with rotation and is not affected by vibration or shock to serve as a reference signal. The temperature sensor measures the temperature in the apparatus to compensate the temperature effect of the gravity accelerometers. The measurement circuit acquires output signals of the sensors and performs cross-correlation processing on the accelerometer components using the reference signal to extract gravity acceleration signals so as to eliminate centrifugal acceleration, vibration, shock and other interferences generated by rotation. The non-interference gravity acceleration signals is used for calculating an inclination angle and a toolface angle of a drilling tool in the rotating state.

Claims

1. A gravity acceleration measurement apparatus mounted on a drilling tool, comprising a measurement circuit, a three-axis gravity accelerometer, a magnetometer, and a temperature sensor, wherein, during operation, the three-axis gravity accelerometer measures acceleration component signals in three mutually orthogonal directions that are in an X-axis, a Y-axis, and a Z-axis, respectively, the magnetometer generates a reference signal that varies with rotation of the drilling tool, the temperature sensor measures a downhole temperature, and the measurement circuit is connected to and acquires output signals from the three-axis gravity accelerometer, the magnetometer, and the temperature sensor, and performs cross-correlation processing of the reference signal and the acceleration component signals compensated using the downhole temperature, and eliminates centrifugal acceleration, vibration, shock and noises generated by rotation to obtain non-interference gravity accelerations along the X-axis and the Y-axis, respectively, and wherein the magnetometer has a sensitive axis perpendicular to the Z-axis, wherein the Z-axis is the rotational axis of the drilling tool, and wherein an inclination angle of the drilling tool is: $\theta =\arctan \left(2\times \frac{\sqrt{{\overline{R}}_{g_x{r}_x}^2+{\overline{R}}_{g_y{r}_x}^2}}{A_z}\right)$ and wherein the toolface angle of the drilling tool is: $\Phi =-\mathrm{arc}\tan \left(\frac{{\stackrel{\_}{R}}_{g_y{r}_x}}{{\stackrel{\_}{R}}_{g_x{r}_x}}\right)$ wherein R.sub.g.sub.x.sub.r.sub.x(τ) is a cross-correlated signal between the reference signal and the gravity acceleration in the X-axis, and ${\stackrel{\_}{R}}_{g_x{r}_x}\left(\tau \right)=\frac{\mathrm{Ax}}{2}\cos \left(\omega \tau +\phi \right),$ R.sub.g.sub.y.sub.r.sub.x(τ) is the cross-correlated signal between the reference signal and the gravity acceleration in the Y-axis, and ${\stackrel{\_}{R}}_{g_y{r}_x}\left(\tau \right)=\frac{\mathrm{Ay}}{2}\sin \left(\omega \tau +\phi \right),$ wherein A.sub.x is the gravity acceleration in the X-axis, A.sub.y is the gravity acceleration in the Y-axis, A.sub.z is the gravity acceleration in the Z-axis, ω is a rotating angular frequency of the drilling tool, φ is an initial phase of an output signal in the X-axis from the accelerometer.

2. The gravity acceleration measurement apparatus of claim 1, wherein the three-axis gravity accelerometer comprises a first gravity accelerometer installed in a first radial direction to the drilling tool along the X-axis, a second gravity accelerometer installed in a second radial direction along the Y-axis, a third gravity accelerometer installed along the Z-axis, wherein X-axis, Y-axis, and Z-axis satisfy a right-handed coordinate system, wherein the three-axis gravity accelerometer is connected with a lowpass filter, wherein, during operation, the lowpass filter performs analog filtering function to the output signals of the three-axis gravity accelerometer to remove frequency component from vibration and shock interference, the filtered signals are acquired by the measurement circuit, and a cut-off frequency of the lowpass filter is related to the frequency bandwidth of the three-axis gravity accelerometer and rotating speed of drilling tool.

3. The gravity acceleration measurement apparatus of claim 2, wherein the measurement circuit further comprises an analog-to-digital converter, a memory, a microcontroller, and a data interface, wherein the analog-to-digital converter is connected with the three-axis gravity accelerometer, the magnetometer, the temperature sensor and the microcontroller, the microcontroller is connected with the memory and the data interface, the lowpass filter is disposed between and connected with the analog-to-digital converter and the three-axis gravity accelerometer, wherein the analog-to-digital converter converts the filtered analog signals of the three-axis gravity accelerometer into digital signals in a format receivable by the microcontroller, wherein the memory is an EEPROM or a FLASH, and the memory stores temperature calibration coefficients, scale factors, offset parameters, and correction coefficients for installation error of the three-axis gravity accelerometer, wherein the microcontroller performs calculations according to an algorithm to obtain the non-interference gravity acceleration, and the data interface is used for inputting and outputting data.

4. The gravity acceleration measurement apparatus of claim 3, wherein the microcontroller comprises a digital filter for filtering out an interference component of the Z-axis gravity accelerometer caused by vibration and shock.

5. The gravity acceleration measurement apparatus of claim 4, wherein the three-axis gravity accelerometer is a quartz flexible accelerometer or a MEMS accelerometer.

6. The gravity acceleration measurement apparatus of claim 1, wherein the three-axis gravity accelerometer is a quartz flexible accelerometer or a MEMS accelerometer.

7. A gravity acceleration measurement and extraction method using the apparatus according to claim 1, comprising: respectively measuring axial Z-axis and radial X-axis, Y-axis gravity accelerations of a drilling tool by using the three-axis acceleration sensor, and generating a signal that varies with rotation and is not affected by vibration or shock to serve as a reference signal by using the magnetometer; measuring the temperature in the apparatus by using the temperature sensor, and performing temperature compensation on the gravity accelerometers; acquiring the output signals of the three-axis gravity accelerometer, the magnetometer and the temperature sensor by a measurement circuit, performing cross-correlation between the X-axis gravity acceleration, the Y-axis gravity acceleration measured by the three-axis gravity accelerometer and the normalized reference signal to eliminate the X-axis and Y-axis interference components generated by vibration and shock; and filtering the interference component measured by the Z-axis gravity accelerometer using the digital lowpass filter in the microcontroller, and obtaining a three-axis gravity acceleration in the rotating state with the influence of the vibration and shock eliminated.

8. The gravity acceleration measurement and extraction method of claim 7, wherein the method employs the apparatus according to claim 2.

9. The gravity acceleration measurement and extraction method of claim 7, wherein the method employs the apparatus according to claim 1.

10. A gravity acceleration measurement and extraction method, wherein the method employs the apparatus according to claim 1.

11. The gravity acceleration measurement and extraction method of claim 1, wherein the gravity acceleration obtained by the method is used for calculating an inclination angle and a toolface angle in the rotating state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of installation positions of a three-axis gravity acceleration sensor and a magnetometer in embodiment 1;

(2) FIG. 2 is a schematic circuit diagram of a gravity acceleration measurement apparatus in a rotating state in embodiment 1;

(3) FIG. 3 is a schematic diagram of a gravity acceleration measurement method in a rotating state in embodiment 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(4) In order that the objectives, technical solutions and advantages of the present invention are clearer and more apparent, the present invention will be further described below in detail in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are merely used for explaining the present invention rather than limiting the present invention. On the contrary, the present invention encompasses any alternatives, modifications, equivalent methods and solutions made within the spirit and scope of the present invention as defined by the claims. Further, in order to make the public better understand the present invention, some specific details are described in detail in the following detailed description of the present invention. It should be understood by those skilled in the art that the present invention may also be fully understood without the description of the details.

Embodiment 1

(5) A gravity acceleration measurement apparatus in a rotating state includes sensors and a measurement circuit, the sensors include three-axis gravity accelerometer, a reference measurement sensor and a temperature sensor, the three-axis gravity accelerometer is connected with a lowpass filter, an included angle between a sensitive axis of the reference measurement sensor and a rotating axis is determined by the sensor type, so that when a drilling tool rotates, the reference measurement sensor can generate periodic variety in the direction of the sensitive axis. The three-axis gravity accelerometer is installed orthogonally to each other, the Z-axis is arranged along the axial direction of the drilling tool, and X-axis and Y-axis are arranged along the radial direction of the drilling tool. The temperature sensor is installed close to the three-axis gravity accelerometer, a magnetometer is used as the reference measurement sensor, the sensitive axis of the magnetometer is parallel to the X-axis, and the installation mode is as shown in FIG. 1. The measurement circuit includes an analog-to-digital converter, a memory, a microcontroller and a data interface, and the connection mode of the apparatus is as shown in FIG. 2.

(6) The method for measuring the gravity acceleration in the rotating state by using the above apparatus is as follows: respectively measuring gravity accelerations of the drilling tool in axial direction Z and radial directions X and Y by using the three-axis gravity accelerometer, and generating a signal that varies with rotation and is not affected by vibration or shock to serve as a reference signal by using the reference measurement sensor; measuring the temperature in the apparatus by using the temperature sensor to perform temperature compensation on the gravity accelerometers; acquiring output signals of the sensors by the measurement circuit, performing cross-correlation on the X-axis gravity acceleration and the Y-axis gravity acceleration measured by the three-axis gravity accelerometer with the normalized reference signal to eliminate the interference components of the X-axis gravity acceleration and the Y-axis gravity acceleration generated by vibration and shock; and meanwhile designing the digital lowpass filter by the microcontroller to filter the interference component of the measurement of the Z-axis gravity accelerometer generated by vibration and shock, and finally obtaining a three-axis gravity acceleration in the rotating state with the influence of the vibration and shock eliminated. The non-interference gravity acceleration obtained by the measurement method can be used for calculating an inclination angle and a tool face angle of the drilling tool in the rotating state. The method is shown in FIG. 3

(7) The gravity acceleration measurement and extraction method in the rotating state is specifically as follows:

(8) (1) Acceleration Signal Measurement

(9) The gravity acceleration measurement apparatus is installed on the drilling tool and rotates around the Z-axis together with the drilling tool while drilling, the rotating angular frequency of the drilling tool is set as ω=2×π×f, the sampling frequency of the analog-to-digital converter is set as

(10) $f_s=\frac{1}{T_s},$
then the output signal of the acceleration sensor installed along the X-axis direction is:
g.sub.x(k)=A.sub.x cos(ω×k×T.sub.s+φ)+n.sub.1(k)=g.sub.x(k)+n.sub.x(k)  (1)
g.sub.x(k) represents an X-axis gravity acceleration signal that includes noise signals. A.sub.x represents the amplitude of the signal from the accelerator installed along the X-axis. k represents the sample point. T.sub.s is the sampling time interval, which is the inverse of the sampling frequency fs. ω is the angular speed, ω=2×π×f, wherein f is the ordinary frequency. φ represents an initial phase of the output signal of the acceleration sensor in the X-axis direction, g.sub.x(k) represents an X-axis gravity acceleration signal without noise, and n.sub.x(k) represents various noise signals including random noise generated by the circuit, centrifugal acceleration generated by the rotation, vibration and shock interferences of the drilling tool, and the like.

(11) The output signal of the acceleration sensor in the Y-axis direction has a 90-degree phase difference from the output signal of the acceleration sensor in the X-axis direction. Therefore, the initial phase of the output signal of the acceleration sensor in the Y axis direction is (φ−90) degrees, then:

(12) $\begin{array}{cc}{\stackrel{\_}{g}}_y\left(k\right)=A_y\cos \left(\omega \times k\times T_s+\phi -\frac{\pi }{2}\right)+n_y\left(k\right)=A_y\sin \left(\omega \times k\times T_s+\phi \right)+n_y\left(k\right)& \left(2\right)\\ {\stackrel{\_}{g}}_y\left(k\right)=g_y\left(k\right)+n_y\left(k\right)& \left(3\right)\end{array}$

(13) g.sub.y(k) represents a Y-axis gravity acceleration signal that includes noise signals. A.sub.y represents the amplitude of the signal from the accelerator installed along the Y-axis. g.sub.x(k) represents a Y axis gravity acceleration signal without noise, n.sub.y(k) represents various noise signals including the random noise generated by the circuit, the centrifugal acceleration generated by the rotation, the vibration and shock interferences of the drilling tool, and the like.

(14) The digital acceleration signal acquired and generated by analog-to-digital converter requires temperature compensation, sensor scale factor and offset correction, installation error correction, etc.

(15) (2) Magnetic Reference Signal Measurement

(16) A magnetometer is installed in the measurement apparatus to serve as the reference measurement sensor, as the signals measured on the horizontal plane (X and Y directions) by the magnetometer are better, the sensitive axis of the magnetometer is installed parallel to the X-axis, the output thereof is used as the reference signal, and the normalized magnetometer signal is expressed as:
r.sub.x(k)=cos(ω×k×T.sub.s)+n.sub.2(k)=r.sub.x(k)+n.sub.r(k)  (4)

(17) (3) Gravity Acceleration Extraction Method Through Correlation Detection

(18) The signals measured by the X-axis and Y-axis accelerometers are processed based correlation detection with the reference signal measured by the magnetometer respectively, and cross-correlation operation is performed on the formula (1) and the formula (4) to obtain a cross-correlation result of the X axis acceleration and the reference signal measured by the magnetometer.

(19) $\begin{array}{cc}{\stackrel{\_}{R}}_{g_x{r}_x}\left(\tau \right)=\frac{1}{N}\underset{k=0}{\overset{N-1}{.Math.}}{\stackrel{\_}{g}}_x\left(k+\tau \right)\times {\stackrel{\_}{r}}_x\left(k\right)=R_{g_x{r}_x}\left(\tau \right)+R_{g_x{n}_r}\left(\tau \right)+R_{r_x{n}_x}\left(\tau \right)+R_{n_x{n}_r}\left(\tau \right)& \left(5\right)\end{array}$

(20) In the formula (5), a sinusoidal signal is irrelevant to random noise, therefore R.sub.g.sub.x.sub.n.sub.r(τ) and R.sub.r.sub.x.sub.n.sub.x(τ) are zero; and because the magnetometer is insensitive to vibrating signals, the coherence between the random noise of the acceleration signal and the random noise of the magnetic reference signal is very weak, and thus R.sub.n.sub.x.sub.n.sub.r(τ)≈0.

(21) $\begin{array}{cc}{\stackrel{\_}{R}}_{g_x{r}_x}\left(\tau \right)=R_{g_x{r}_x}\left(\tau \right)=\frac{A_x}{2}\cos \left(\mathrm{\omega \tau }+\phi \right)& \left(6\right)\end{array}$

(22) Similarly, the cross-correlation operation is performed on the formula (3) and the formula (4) to obtain a correlation signal of the Y-axis acceleration and the reference signal measured by the magnetometer.

(23) $\begin{array}{cc}{\stackrel{\_}{R}}_{g_y{r}_x}\left(\tau \right)=\frac{1}{N}\underset{k=0}{\overset{N-1}{.Math.}}{\stackrel{\_}{g}}_y\left(k+\tau \right)\times {\stackrel{\_}{r}}_x\left(k\right)=R_{g_y{r}_x}\left(\tau \right)+R_{g_y{n}_3}\left(\tau \right)+R_{r_x{n}_2}\left(\tau \right)+R_{n_2{n}_3}\left(\tau \right)& \left(7\right)\\ {\stackrel{\_}{R}}_{g_y{r}_x}\left(\tau \right)=R_{g_y{r}_x}\left(\tau \right)=\frac{A_y}{2}\sin \left(\mathrm{\omega \tau }+\phi \right)& \left(8\right)\end{array}$

(24) Comparing the formula (1) with the formula (6), we obtain:
g.sub.x(t)=2×R.sub.g.sub.x.sub.r.sub.x(t)=A.sub.x cos(ωt+φ)  (9)

(25) The formula (9) is the output signal of the acceleration sensor in the X-axis direction after the noise is removed.

(26) Comparing the formula (2) with the formula (8), we obtain:
g.sub.y(t)=2×R.sub.g.sub.y.sub.r.sub.x(t)=A.sub.y sin(ωt+φ)  (10)

(27) The formula (10) is the output signal of the acceleration sensor in the Y-axis direction after the noise is removed. As the Z-axis is the rotating axis, in view of the fact that the acceleration of the Z-axis direction varies only when the inclination angle changes in the actual drilling process, and the inclination angle changes very slowly, and thus the acceleration signal of the Z-axis can be regarded as a direct current signal which changes very slowly, and the digital lowpass filter is designed in the microcontroller to further filter the vibration and shock interferences.

(28) The gravity acceleration further obtained by the measurement method can be used for calculating the inclination angle and the toolface angle of the drilling tool.

(29) (4) Method for Calculating the Inclination Angle and the Toolface Angle

(30) The inclination angle is:

(31) $\begin{array}{cc}\theta =\arctan \left(\frac{\sqrt{g_x^2+g_y^2}}{g_z}\right)=\arctan \left(2\times \frac{\sqrt{{\stackrel{\_}{R}}_{g_x{r}_x}^2+{\stackrel{\_}{R}}_{g_y{r}_x}^2}}{A_z}\right)& \left(11\right)\end{array}$

(32) The toolface angle is:

(33) $\begin{array}{cc}\Phi =-\arctan \left(\frac{g_y}{g_x}\right)=-\arctan \left(\frac{{\stackrel{\_}{R}}_{g_y{r}_x}}{{\stackrel{\_}{R}}_{g_x{r}_x}}\right)& \left(12\right)\end{array}$
g.sub.z represents the Z-axis gravity acceleration signal subjected to digital lowpass filtering.