Research on a Measurement Method for Downhole Drill String Eccentricity Based on a Multi-Sensor Layout

Abstract

The drill string used in drilling is in a complex motion state downhole for several kilometers. The operating attitude and eccentricity of the downhole drill string play important roles in avoiding downhole risks and correcting the output of the imaging measurement sensor while drilling (IMWD). This paper proposes a method for measuring eccentricity while drilling using two sets of caliper sensors coupled with a fiber-optic gyroscope for continuous attitude measurement, which is used to solve the problem of the quantitative measurement of complex eccentricity that changes in real-time downhole. According to the measurement and calculation methods involved in this article, we performed simulations of the attitude of the drill string near where the IMWD tool is located in the wellbore under a variety of complex downhole conditions, such as centering, eccentricity, tilt, buckling, rotation, revolution, etc. The simulation and field test results prove that the distance between the imaging while drilling sensor and the borehole wall is greatly affected by the downhole attitude and revolution. The multi-sensor layout measurement scheme and the data processing based on the above-mentioned measurement involved can push the drill collar movement and eccentricity matrix specifically studied downhole from only qualitative estimation to real-time measurement and quantitative calculation. The above measurement and data processing methods can accurately measure and identify the local operating posture of the drill string where the IMWD sensor is located, and quantitatively give the eccentric distance matrix from the measuring point to the borehole wall required for environmental correction of the IMWD sensor.

Automated Stratum Interface Detection Using the Optimized Drilling Specific Energy through Self-Adaptive Logistic Function

“…Due to the susceptibility of individual data to disturbances, a more practical approach to reflecting the rate of change of indicators is to utilize the coefficient of variation for data intervals [16]. Figure 2 demonstrates the division of the drilling data into intervals of a specific length.…”

“…The coefficient of variation serves as a dimensionless measure reflecting the degree of data fluctuation, which can be expressed as Equation (4). Due to the susceptibility of individual data to disturbances, a more practical approach to reflecting the rate of change of indicators is to utilize the coefficient of variation for data intervals [16]. Figure 2 demonstrates the division of the drilling data into intervals of a specific length.…”

“…Moreover, to ensure the consistency of the corresponding displacement lengths of intervals, the data lengths of the intervals at the three penetration speeds were 16, 10, and 8, respectively. Due to the susceptibility of individual data to disturbances, a more practical approach to reflecting the rate of change of indicators is to utilize the coefficient of variation for data intervals [16]. Figure 2 demonstrates the division of the drilling data into intervals of a specific length.…”

“…Figure16. The interval coefficients of variation before and after the optimization of the driving parameters.…”