Horizontal well geosteering method

The invention relates to the technical field of petroleum and natural gas drilling exploration and development, in particular to a horizontal well geosteering method. The method comprises the following steps that (1) an inclination angle theta is calculated according to two adjacent layer crossing points of a horizontal well track, the inclination angle theta is equal to arctan (delta H/delta L), and delta H and delta L are the vertical depth difference and the horizontal plane projection distance of the two adjacent layer crossing points respectively; (2) the dip angle theta is compared with the stratum apparent dip angle range alpha min-alpha max of the horizontal well target section, and the initial value of the stratum apparent dip angle range is obtained through seismic data; (3) the drilling angle is adjusted; when [theta] is greater than or equal to [alpha] min and less than or equal to [alpha] max, if the previous layer crossing point is located at the top/bottom of the reservoir, performing inclinati