Combining Pore Architecture and Sonic Velocity Response to Predict Reservoir Quality: An Example from a mid-Continent Mississippian Carbonate

Beth Vanden Berg, Michael Grammer, Gregor Eberli, and Ralf Weger

Laboratory measured sonic velocities in carbonates are related to porosity, pore architecture, and diagenetic alterations, which are in turn related to the depositional environment and basin history. Understanding how these properties are related allows quantitative correlation of sonic velocity response to permeability. Predictable relationships between sonic velocity response and porosity are recognized in carbonate rocks, but the data have significant scatter. For example, a porosity of 40% can produce an acoustic velocity response varying from 2400-5000 m/s. The reason for this scatter is variations in pore architecture, depositional fabric, and diagenetic history. Classification by primary pore type (intergranular, moldic etc…) decreases the scatter but not enough to establish a quantitative relationship. Additional controls include the percentage of micro- and macro-porosity, dolomitization, non-carbonate mineralogy, and pore geometry. Because of this variability, laboratory measured sonic velocity response must be compared to petrophysical properties unique to each reservoir. The Mississippi Lime play, a mid-Continent Mississippian carbonate, is primarily located in Oklahoma and Kansas. Depositional environments vary from a deep basin to carbonate slope and ramp. Regional depositional settings and diagenetic alterations are mostly agreed upon, however details controlling reservoir quality are poorly understood. Petrophysical analyses of a Mississippi Lime outcrop will be integrated with laboratory sonic velocity response to quantify the porosity-pore architecture- permeability relationship. Laboratory analysis and field observations will be correlated with high resolution sequence stratigraphic studies to correlate results with specific facies and depositional environments. Quantification of sonic velocity relationships will provide valuable insight into the reservoir characterization and how to target key intervals within the Mississippian play. 

AAPG Search and Discovery Article #90176©AAPG Mid-Continent Meeting, Wichita, Kansas, October 12-15, 2013