| In the progress of wellbore anti-collision, a common approach is calculating wellbore trajectory to determine the positional relationship between adjacent wells. Describing trajectory according to inclinometer data, a magnetic inclinometer is the main measuring equipment at present. when drilling near the other well, the casing of adjacent well will be magnetized by the earth’s magnetic field, causing local magnetic anomalies, thereby causing inclinometer data distortion, then leading to directional errors. It is very to meet the requirements of infill wells anti-collision if based on inclinometer data calculation. Therefore, It is necessary to study the influence of magnetic interference environment on the well trajectory magnetic measurement parameters and the method of judging adjacent well location.Adjacent well’s casing is magnetized by geomagnetic in the earth’s magnetic field environment, then magnetizing magnetic field appears,causing the data of the geomagnetic anomaly and azimuth angle distortion in the area nearby, so that the local area magnetic field intensity, the direction and the magnetic declination will be abnormal. Azimuth is calculated according to inclinometer measurement magnetic parameters, and the azimuth is a function of the geomagnetic component and the magnetic declination.The azimuth is also interfered, leading to azimuth data distortion. Azimuth distortion consists of two parts. One is the calculation data distortion caused by the magnetic distortion, the other distortion is caused by magnetic declination anomaly, which is caused by magnetic anomalies. Geomagnetic declination calculated by the abnormal data is always pointing to the magnetic anomaly sources, which also provided information for determining the orientation of adjacent wells.On one hand, the magnetic anomalies caused by casing as the anomaly resource interferes with the inclinometer measurement data, on the other hand, it provides information to determine the orientation of adjacent well. Magnetic field intensity, the gradient, gradient tensor and tensor invariants. With the proximity of the different measuring points and orientation of objects with magnetic, magnetic anomalies have different decay rates. Various magnetic anomalies values reflect different characteristic information. Based on this, the orientation of adjacent wells can be determined. With the analysis of the characteristics of the magnetic field strength, gradient tensor and tensor invariants information, it is can be seen that the different degrees of these features reflect the information of adjacent wells’ azimuth and the distance, and the casing’s different tilt angles also have some impact on these values, but the basic information is same.Magnetic field gradient tensor and tensor invariants have distinct features, and contains more information. Gradient tensor and tensor invariants affected by the earth’s magnetic field direction is relatively small, as the earth’s magnetic field gradient is negligibly small, So the magnetic field gradient measurement mainly reflects the abnormal magnetic field gradient. Magnetic field gradient tensor can clearly reflects inclinometer’s position and distance. Magnetic field gradient tensor invariant has the common features of the magnetic field gradient tensor, which is a comprehensive reflection of the magnetic field gradient tensor. The abnormal area is superimposed area of tensor abnormalities, and tensor invariants reflects the common characteristics of the magnetic field gradient tensor. Through the analysis of the magnetic field gradient, the explanation effect of magnetic field data can be improved and supplemented effectively. According to the magnetic field strength anomalies and the changes of magnetic field gradient, the position of the sleeve relative to the measuring point can be determined. By the changes of abnormal magnetic field strength and magnetic field gradient, the position of the adjacent well relative to the measuring point can be determined. |
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