In-Situ Validation of PSDM Seismic Volumetric Curvature as a Tool for Paleokarst Heterogeneity Studies: Results from an Extended-Reach Lateral
Rush, Jason; Watney, Willard L.; Hedke, Dennis E.; Doveton, John; Fazelalavi, Mina
This DOE-funded project evaluates the utility of seismic volumetric curvature (VC) for predicting stratal and structural architecture diagnostic of paleokarst reservoirs. VC has been championed for identifying faults (offset <¼ λ) that cannot be imaged by conventional 3-D seismic attributes such as coherence. The objective of this research is to prove-up VC-techniques for reducing uncertainties in reservoir compartmentalization studies and seal risk assessments. A 2000-ft horizontal lateral was purposefully drilled across VC-imaged lineaments—interpreted to record a fractured and fault-bound doline—to physically confirm their presence.
The 15-mile² study area is located in southeastern Bemis-Shutts Field, which is situated along the crest of the Central Kansas Uplift (CKU) in Ellis County, Kansas. The uppermost Arbuckle (200+ ft) has extensive paleokarst including collapsed paleocaverns and dolines related to exceedingly prolonged pre-Simpson (Sauk-Tippecanoe) and/or pre-Pennsylvanian subaerial exposure. A lateral borehole was successfully drilled across the full extent (~1100 ft) of a VC-inferred paleokarst doline. Triple combo (GR-neutron/density-resistivity), full-wave sonic, and borehole micro-imager logs were successfully run to TD on drill-pipe. Results from the formation evaluation reveal breccias (e.g., crackle, mosaic, chaotic), fractures, faults, vugs (1-6 in), and unaffected host strata consistent with the pre-spud interpretation. Well-rounded pebbles were also observed on the image log. VC-inferred lineaments coincide with 20-80-ft wide intervals of high GR values (100+ API), matrix-rich breccias, and faults.
Interpretations of the PSDM volume, VC-attributes, core, and wireline logs provide an integrative assessment of karst landscape evolution along the CKU. In contrast to the southeastern part of the study area, the northwestern part is characterized by large dolines (>1000-ft wide) that coincide with radiating lineaments as shown in VC-attribute maps. Dolines likely functioned as small, local river basins (i.e., interior drainage). Surface water may have been focused into dolines along channels that preferentially formed along radial fractures created by sagging and brittle failure within paleocavern roofs. Geomorphic evidence suggests that a karsted plateau developed where runoff was diverted into a groundwater system via dolines (i.e., disappearing streams), moved downdip along an aquitard, and emerged as springs along an escarpment.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013