Abstract
The Denver-Julesburg Basin in northern Colorado is an unconventional hydrocarbon play utilizing horizontal wells to access several targets, known locally as benches, including the Niobrara B-Chalk. The need to navigate and optimally place completion packers in the unconventional play with complex, laminated rock structure and sub-seismic faulting is important to effectively stimulate productive rock. While bulk gamma is primarily used to correlate the formation, more advanced real-time LWD technology is proposed to navigate effectively and maintain the wellbore within the specific target chalk. A high resolution LWD electrical imaging tool is also employed to optimize the completion strategy and confirm real-time interpretations.
An azimuthal gamma ray image was used to determine formation bed dip and stratigraphic complexity along with two different resistivity measurements to correlate position within the reservoir. Thedata was transmitted in real-time to a remote geo-steering center where a Reservoir Navigation Engineer incorporated the data into the geological model and provided the operator with real-time steering recommendations for remaining within the zone of interest. Additionally, the data were used toidentify faults and interpret the fault-throw direction and distance.
The well was drilled with 85% of the lateral section placed in a 10-ft-thick target zone compared to less than 50% in offset wells navigating with gamma only. This was accomplished despite crossing over one sub-seismic fault and having relative formation dips varying from 88 to 92 degrees.
The improved net-to-gross was a result of the utilization of azimuthal gamma, multiple propagation resistivity, and the real- time Reservoir Navigation Service (RNS). The increased "in-zone" footage indicates this method provided a significant advantage over gamma-only measurements when navigating such complex and faulted formations. Post well, the high resolution LWD electrical image logs were used to confirm the faults and determine packer placement for optimal completionefficiency.
