针对现行井眼定位方法存在的问题,提出真三维井眼定位方法,并进行算例分析。现行定位方法以网格北作为指北基准,基于地图投影坐标进行水平面定位,基于高程坐标进行垂向定位,且二者相互独立,只使用一点处的子午线收敛角和磁偏角来归算全井的井眼轨迹,存在固有缺陷和误差。基于地球椭球及其解算原理,揭示了井口坐标系与大地坐标系及高程坐标系之间的转换关系,提出了采用真北作为指北基准的真三维井眼定位方法。算例分析结果表明,现行定位方法算得的靶点垂深偏小、水平位移偏大,与真三维定位方法相比存在较大误差。真三维井眼定位方法从根本上解决了现行定位方法存在的问题,能精准定位靶点与井口间的相对位置,可显著提高井眼轨迹设计的精确性和可靠性。图3表6参16
In view of the problems existing in the current wellbore positioning method, a true three-dimensional wellbore positioning method was presented, and an example for analysis was given. The current positioning method uses the grid north as the reference datum to the north, positions in the horizontal plane based on the map projection coordinates, and positions in the vertical direction based on the elevation coordinates. It has inherent defects and errors, as the two positionings above are independent of each other, and only use the constant meridian convergence and constant magnetic declination at the wellhead to calculate the borehole trajectory for the whole well. Based on the earth ellipsoid and its calculating principle, the transformation relationship between the wellhead coordinate system, geodetic coordinate system and elevation coordinate system was revealed, and the true three-dimensional wellbore positioning method using the true north as the reference datum to the north was presented. Analysis results of an example show that the current positioning method yields a smaller vertical depth and a larger horizontal displacement for the target, and produces larger errors compared with the true three-dimensional positioning method. The true three-dimensional positioning method has fundamentally solved the problems existing in the current positioning method, accurately positioning the relative location between the target and the wellhead, and significantly improves the accuracy and reliability of borehole trajectory design.
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