A seismic attribute study to assess well productivity in the Ninilchik field, Cook Inlet basin, Alaska

Abstract

Coal bed methane which has formed in the Tertiary Kenai Group strata has been produced from the Ninilchik field of Cook Inlet, Alaska since 2001. Ninilchik field is located on the eastern margin of the central Cook Inlet along the Kenai Peninsula. Cook Inlet is a forearc basin and is characterized by northeast trending anticlines with upwards of 10,000 feet of Late Oligocene and younger, non-marine sediments. Highly variable well production within the Oligocene to Miocene Tyonek formation of the Kenai Group has been a source of uncertainty. A series of seismic attributes visualized in Schlumberger's Petrel® software were studied on a 3D seismic volume to investigate potential structural and stratigraphic controls for the observed, variable well production. Geometrical seismic attributes, such as variance/coherence, dip, and azimuth, are the primary attributes used in pattern recognition to investigate the formation properties near well locations. Production data were integrated with the seismic attributes on five distinct well groups targeting sand reservoirs in the Tyonek formation. A complete seismic attribute evaluation for all well groups is not feasible due to some data quality issues. Overall, structural properties such as folding and faulting are large scale enough to be confidently imaged by seismic attributes. Amplitude or envelope strength mapping to detect fluid changes poses problems in the coal-dominated stratigraphy. No correlation between the source rock thickness and well production quality is evident from log analysis. Variance volumes co-rendered with the ant tracking attribute, a method for enhancing geologic discontinuities, are shown to be useful for highlighting faults in low signal to noise seismic. Bottom-hole locations nearest the anticline fold axis tend to have the highest production histories due to the increased stresses and faulting near the fold crest.