Confidence Limits Associated With Values of the Earth's Magnetic Field used for Directional Drilling

Macmillan, Susan; McKay, Allan; Grindrod, S.J.

doi:10.2118/119851-ms

Cited by 5 publications

(3 citation statements)

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“…As shown in the Earth field observation coordinates system in Fig. 1 (Finlay et al, 2010;Macmillan et al, 2009), the inclination and azimuth of the collision segment of the target well are b and a, respectively. The drill bit in the drilling well drills vertically along a distance of L t (unit: m) from a specific depth before colliding with the target well.…”

Section: Collision Avoidance Modelmentioning

confidence: 99%

“…The two electromagnets are situated symmetrically around the center of magnetometer, and the distance between them is l. The axes of the two electromagnets are parallel, while the current in the coils run in opposite directions, creating magnetic moments in the two magnetic sources equal in magnitude and opposite in direction. Therefore, the total magnetic field's intensity as detected by triaxial magnetometer is 0 when there is no other outer magnetic field, ensuring that the electromagnetic collision avoidance system provides a relatively strong magnetizing field without affecting the measurement by triaxial magnetometer (Diao et al, 2011;Liu and Wang, 2011;Finlay et al, 2010;Macmillan et al, 2009;Lousberg et al, 2009). Assuming that the radius and turn of the coil are R and n 1 , respectively, and the magnetic moment of the coil is amplified by the iron core up to n 2 times the original value.…”

Section: Structure Of Instrumentmentioning

confidence: 99%

“…When no casing exists around the triaxial magnetometer, or the casing is too far away, the Earth field and the field of the casing induced by electromagnets are both too weak, resulting in a magnetic difference value that is not sufficient to determine whether casing exists (Macmillan et al, 2009;Lousberg et al, 2009;Yang et al, 2010). Assuming that the existence of casing can be determined when peakepeak value is larger than 1 nT, then the effective detection range of this collision avoidance method is approximately 8 m (see the peakepeak value where borehole distance is 8 m in Fig.…”

Section: Numerical Examplesmentioning

confidence: 99%

See 2 more Smart Citations

An investigation of electromagnetic anti-collision real-time measurement for drilling cluster wells

Gao

Diao

2015

Journal of Natural Gas Science and Engineering

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Section: Collision Avoidance Modelmentioning

confidence: 99%

Section: Structure Of Instrumentmentioning

confidence: 99%

Section: Numerical Examplesmentioning

confidence: 99%

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An investigation of electromagnetic anti-collision real-time measurement for drilling cluster wells

Gao

Diao

2015

Journal of Natural Gas Science and Engineering

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Probability of Wellbore Intercept Made Easy

Codling

2018

IADC/SPE Drilling Conference and Exhibition

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Wellbore intercept probability calculations are important not only for avoiding collisions but also for relief-well planning and planning for wellbore reentry in abandonment projects. This study reviews the current methods for calculating probability and their sensitivity to the input variables. A probability of intercept calculation is presented that is proven, robust, and can be implemented in a spreadsheet as input-wellbore positions and survey-error dimensions. Given the lack of availability of empirical wellbore collision-frequency data, it was necessary to model the wellbore-intercept scenario using a Monte Carlo simulator constructed by breaking the two wellbores into short segments. The validity of the simulator is highly sensitive to the probability distribution of the input-survey errors. The input-probability distribution of well separations in the high side and lateral directions is determined from survey-comparison studies for both systematic and random-error sources. The simulator is used to compare the accuracy and reliability of different probability integration types and sensitivity to the input data and distribution of errors. It is observed from survey comparisons that the distribution of survey inclination and azimuth errors behave as "heavy tailed" probability distributions such as Laplace or Student's t. This increases the probability of intercept at higher sigma levels than the previously assumed normal distribution. The results of this study exhibit the sensitivity of the probability result to the degree of sophistication of the probability calculation from simple one-dimensional (1D) projection to three-dimensional (3D) integration of probability density. There is a law of diminishing returns with the sensitivity of complex models being lost in the reliability of the input-error values and assumptions on probability distributions. One observation is that there is no "pedal curve" effect for high-angle well crossings. The simple point-to-point collision calculations using this vector method do not include the confidence in the relative direction of the two wellbores. Therefore, probability calculations and separation-factor calculations that engage the pedal-curve distances are overly conservative. A reliable prediction of wellbore-intercept probability is achieved using a relatively simple method. This study shows the importance of the angle of intercept to enhance interception probability for relief wells and abandonment re-entry operations.

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