# Research on Intelligent Optimization of Wellbore Trajectory in Complex Formation
## 2 Related Work
### Key Parameters of Drilling Trajectory  
Well depth is the basic parameter to describe the extension degree of wellbore trajectory in the vertical direction. It is defined as the length of wellbore trajectory from the wellhead to the current measuring point. Generally, \(D_{m}\) is expressed in meters. In the actual measurement, the change of well depth is reflected by the well section. The well section refers to the difference of well depth between two adjacent measuring points, which is recorded as \(\Delta D_{m}\). For the two measuring points in the same measuring section, they are divided into upper measuring points and small measuring points according to the size of well depth. The calculation of well depth increment refers to the difference between the well depth of the lower measuring point and the well depth of the upper measuring point, namely \(\Delta D_{m}=D_{mB}-D_{mA}\). This parameter provides the basis for the subsequent calculation of the vertical depth and horizontal projection data of the wellbore trajectory, and this parameter is also a key indicator for evaluating the vertical development of the wellbore trajectory. The deviation angle is a quantity used to measure the degree of deviation of the wellbore trajectory from the vertical direction in space. It is the direction of the wellbore formed by the tangent of a certain point on the axis of the wellbore trajectory along the forward direction of the wellbore trajectory. The angle between the line and the gravity line is expressed by the Greek letter \(\alpha\), and the unit is degrees. In an inclination section, the change of the deviation angle is described by the increment \(\Delta\alpha\). The calculation method is that the deviation angle of the lower measuring point is subtracted from the deviation angle of the upper measuring point; that is, the deviation angle increment of the \(AB\) section is \(\Delta\alpha=\alpha_{B}-\alpha_{A}\), where \(\alpha_{A}\) is the deviation angle of the \(A\) point and \(\alpha_{B}\) is the deviation angle of the \(B\) point. Accurate measurement and analysis of well deviation angle is helpful to grasp the inclination trend of the wellbore trajectory in three-dimensional space, which is of great significance in designing a reasonable wellbore trajectory and avoiding wellbore collision. Refer to Figure 1, a well deviation angle diagram, for a visual representation of the well deviation angle. The well deviation azimuth refers to the angle between the tangent horizontal projection of a measuring point on the axis of the wellbore trajectory and the north direction. It is expressed by the letter \(\varphi\), and the unit is degrees, in which \(0<\varphi<2\pi\) and its increment \(\Delta\varphi\) are the difference between the well deviation azimuth of the lower measuring point and the well deviation azimuth of the upper measuring point; that is, \(\Delta\varphi=\varphi_{B}-\varphi_{A}\), in which \(\varphi_{B}\) represents the well deviation azimuth of the point \(B\), \(\varphi_{A}\) represents the well deviation azimuth of the point \(A\). The deviation azimuth determines the direction of the wellbore trajectory on the horizontal plane. In the actual measurement, a magnetic inclinometer is commonly used to measure the deviation azimuth based on the magnetic north of the Earth. However, due to the magnetic deviation angle in the magnetic north and the north direction, it is necessary to correct this to obtain the true azimuth. The magnetic declination is divided into east magnetic declination and west magnetic declination. The corrected true azimuth is calculated by the difference between the magnetic azimuth and the east magnetic declination or the west magnetic declination. In addition, the azimuth of the well deviation can also be expressed by quadrant angle; that is, the angle between the azimuth line of well deviation and the geographic north or south azimuth line.