Method of maintaining a borehole in a stratigraphic zone during drilling

Abstract

Directional drilling techniques allow a borehole to be drilled downwardly, horizontally and even upwardly. The present invention provides a method of navigating a borehole that can be drilled with directional drilling techniques. The direction in which the borehole is drilled is determined relative to a stratigraphic target zone. By so navigating, the borehole can enter the target zone and be extended inside of the target zone. First, an offset log is obtained. Then a log of the borehole is obtained. Correlation points along the lengths of the borehole are selected. At each correlation point, the true stratigraphic depth of the borehole is determined, using the offset log. Knowing the true stratigraphic depth of the borehole allows the location of the target zone relative to the borehole to be determined, wherein the direction that the next segment of the borehole should be drilled is determined.

Dependencies are inferred from the claim text.