Correct wellbore placement is critical to the economic success of the well. Given the nature of the bare minimum total gamma and sparse 90' survey data used in most horizontal drilling applications, even the best geosteering geologists often find themselves running multiple simultaneous interpretations in hope that one will start to make sense as new data comes in.
Employment of azimuthal gamma imaging in conjunction with continuous inclination brings clarity to stratigraphic position, bed dip, faults, and zones where bedding is laterally discontinuous or completely absent. In many of these situations geosteering in its traditional sense cannot be executed. Through enhanced visibility of the subsurface by azimuthal gamma imaging, geological anomalies can be quickly identified and handled in the best possible manner. Furthermore, in many cases, the status quo of 2D geosteering software creates further confusion and uncertainty as it provides no indication beyond a projection as to what may lie ahead. Also, displaying cross sections in vertical section rather than curtain view, projects the wellpath onto a plane where the geological character may be different due to structure adjacent to the vertical section line.
Utilizing azimuthal gamma imaging data to identify faults, laterally continuous/discontinuous bedding, and high energy sedimentary deposition improves geological interpretation confidence. Furthermore a protocol has been developed to identify and handle challenging geosteering situations using a model based 3D geosteering solution with multiple well and seismic surface inputs providing options beyond traditional correlation alone.
Geosteering in its traditional sense involves correlation of logging data in deviated or horizontal wells to a nearby vertical typelog that characterizes the zone of interest. Correlating against a typelog requires that bedding thicknesses and gamma character of the target well be close to that of the typelog (which may be offset by many miles), otherwise the resultant geosteering interpretation will have unreasonable bed dips that will not accurately reflect that of the target lithology being drilled.
