A Seismic Attribute Study to Assess Well Productivity in the Ninilchik Field, Cook Inlet Basin, Alaska

Coal bed methane formed in the Tertiary Kenai Group has been produced from the Ninilchik field of Cook Inlet, Alaska since 2001. Cook Inlet exhibits a foreland basin geometry bounded by the Alaska Range to the northwest and the Chugach Mountain terrane to the southeast. Ninilchik field is located on the eastern margin of the central Cook Inlet on the Kenai Peninsula, approximately 90 miles southwest of Anchorage, Alaska. The field is characterized by a northeast-southwest trending, elongate anticline with 10,000 feet of Late Oligocene and younger, non-marine sediments.

Highly variable well production within the Oligocene to Miocene Tyonek formation has been a source of uncertainty. An investigation into the causes for variable well production is done by analysis of a 3D seismic data volume using seismic attribute visualization tools in Schlumberger's Petrel software. The 3D seismic volume covers approximately 128 square miles of onshore and offshore data. Geometrical seismic attributes, such as variance/coherence, dip, and azimuth, are the primary attribute tools used to investigate variations in the formation properties in the vicinity of the borehole locations. Five well groups, each with multiple boreholes reaching sufficient depths to the Tyonek sands, were examined individually. Production history data was correlated with various seismic attribute displays through visual observations.

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 accurately imaged by seismic attributes. Amplitude mapping is shown to be reasonably successful for tracking organic rich coal bed layers where data quality permits. Amplitude dimming, occurring where impedance contrast decreases between layers, is shown to be an indicator for the presence of gas above coal. Variance volumes combined with an ant tracking attribute are shown to be useful in low signal to noise areas for highlighting fault locations. Bottom-hole locations nearest the anticline axis, highlighted by the structural azimuth attribute, tend to have the highest production histories.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California