| 主权项 |
1. A method of drilling a borehole, wherein the drilling tool includes a gamma ray tool providing gamma ray data within a natural gamma ray sphere of influence, the method comprising the steps of:
a) selecting a target formation layer in a formation, wherein the formation includes two or more formation layers having different lithologies; b) proposing a borehole trajectory to the target formation layer; c) drilling the borehole and obtaining real time directional and natural gamma ray data at multiple borehole positions along the borehole trajectory; d) processing the real time directional and natural gamma ray data for each of the borehole positions; e) locating a generally horizontally extending boundary of the target formation layer, wherein the boundary is located between the target formation layer and an adjacent formation layer having a different lithology; f) determining a tangent line extending between a first circle having a radius ri about a first point on the borehole trajectory and a second circle having a radius ri about a second point on the borehole trajectory, wherein the first point is located above the boundary of the target formation layer and the second point is located below the boundary of the target formation layer, wherein the distance between the first and second points is greater that 2ri, and ri is the radius of the gamma ray sphere of influence, and wherein the tangent line represents the boundary of the target formation layer; g) extrapolating the location of the boundary of the target formation layer ahead of the drilling tool; and h) adjusting the borehole trajectory based on the extrapolated location of the boundary of the target formation layer to maintain the borehole within the target formation layer. |
