3-D ANALYSIS OF POROSITY AND PERMEABILITY OF A TIGHT CARBONATE FORMATION, LOWER HENRYHOUSE FORMATION, HUNTON GROUP, CLEVELAND COUNTY, OKLAHOMA

The Hunton Group, central Oklahoma, contains thick reservoir facies in the Frisco Limestone, the uppermost formation in the Group. The Frisco Limestone and formations in the Chimneyhill Subgroup at the base are potential zones of underground storage of fluids, including wastewater and CO₂. Other intervals such as relatively clean carbonates within the Lower Henryhouse Formation lack the porosity and natural permeability to facilitate the storage and transmission of fluids. Core analysis of these potential seal intervals confirm very low matrix porosity values and extensive cementation of fractures resulting in very low storage capacity for fluids, but high potential as internal seals to vertical fluid migration within the Hunton Group. In addition to these low-permeability low-clay content carbonates, there are several one-foot scale (30 cm) intervals in the Lower Henryhouse Formation with significantly higher clay content that contribute to seal integrity and impede unwanted vertical migration of fluids. Most of the wireline logs in the area do not show any indications of open fractures in the Lower Henryhouse Formation and this interval is easily correlated over more than 40 square miles (100 sq kilometers).

Unless there are external factors such as faulting or improperly cemented wellbores, this type of internal seal should impede vertical migration of fluid injectate within the Hunton Group. Impeding vertical migration is important in areas like central Oklahoma with multiple stacked reservoirs where upward or downward movement of fluids to permeable intervals could result in its lateral migration to nearby wells. The importance of internal seals that prevent downward migration of disposed wastewater from oilfield operations is illustrated by the induced seismicity of the past decade in Oklahoma and Kansas, where migration of wastewater into the basement triggered earthquakes at depths far below the depth of injection.