With the increase of oil and gas resources exploitation, the difficulty of resource exploration and exploitation has also increased gradually, so the measurement accuracy of directional drilling trajectory has put forward higher requirements. The traditional drilling inclinometer cannot achieve real-time continuous dynamic measurement of drilling tool attitude, while the sensor measurement position is far away from the drill bit, and there are errors in the measured information, which cannot get accurate borehole trajectory information, thus will affect the whole drilling process.

To solve the problem of dynamic well slope angle measurement accuracy near the drill bit position, Yang Hai's research team from China proposed a dynamic and accurate measurement method based on Unscented Kalman Filter (UKF) and Complementary Filter (CF) to measure the well slope angle and tool face angle with drilling. To obtain more accurate measurement data, the team usedIMU (Inertial Measurement Unit)as a measurement tool and different filtering processes are applied to the IMU measurement data.

Diagram of the installation direction of the well inclination measurement sensor

The team used a limiting filter to filter out the shock noise from the accelerometer, a low-pass filter to filter out the high-frequency noise from the gyroscope, and then used a traceless Kalman filter to filter out most of the vibration noise in the IMU, and then used the angular velocity signal measured by the gyroscope and the acceleration signal for complementary filtering to eliminate the zero bias interference signal to calculate the well inclination angle and tool surface angle.

To verify the noise suppression capability of the proposed method and the accuracy of gravitational acceleration signal extraction, the team conducted three experiments:

①Algorithm verification using MATLAB: After the gyroscope angular velocity signal extracted by the UKF+CF based method, the error between the calculated result and the actual well inclination angle is ±0.2°.

②The experimental test was conducted using a rotary vibration test system (Figure 2). The actual well slope angle during the experiment was set to 30°, the drilling tool speed was 150 r/min, and the IMU sampling rate was 200 Hz. The maximum error of the calculated well slope angle was -0.08°, and the overall accuracy was close to ±0.1°.

③The performance of the algorithm was tested using the actual measured data stored during downhole work with the field drilling near-bit follow-through measurement instrument and derived from the surface. The results show that the test results using field data are basically consistent with the above experimental results, and the accuracy of the UKF+CF method to measure the well inclination is ±0.2°.

In order to verify the performance of the method under different well slope angles and different rotational speeds, the team also conducted additional experiments by adjusting the well slope angles to 10°, 30°, 45° and 60° and setting the drilling tool rotational speeds to 60r/min, 120r/min, 200r/min and 300r/min, respectively. The experimental results are basically consistent with the previous ones, and the well slope angle measurement accuracy is ±0.2°, with the maximum error of ±0.19°. It is evident that the method has high angle measurement accuracy, and the measurement accuracy is not limited by the drilling tool speed, which is very suitable for continuous well slope angle measurement at different speeds.