ABSTRACT
An understanding of the mechanical properties of petroleum reservoirs is important for drilling, well stimulation and horizontal well development. Static and dynamic rock mechanical properties were measured on a suite of core samples taken through the Chase and Council Grove carbonate sequences of the Hugoton and Panoma fields, Kansas. The purpose of the study was to characterize the mechanical properties of the different facies and calibrate the dynamic mechanical properties so acoustic well logs from other wells can be utilized more effectively in determining areal and lithologic variation in mechanical properties of the field.
The mechanical properties of rocks can be measured in the laboratory from triaxial tests ("static" tests) or they can be estimated from wireline measurements of compressional and shear acoustic velocities and rock density ("dynamic" tests). Static measurements on cores are much more indicative of the mechanical properties of the reservoir than the dynamic results, however, the information from acoustic well logs covers much more of the reservoir than core measurements and is less expensive. Since there can be significant differences between static and dynamic values, it important to be able to translate the "dynamically" derived mechanical properties to the static values which better represent the reservoir.
Results of the tests show that Young's modulus correlates strongly with lithofacies and porosity. The Chase and Council Grove carbonate sequences can be separated into six "mechanical facies", defined by their modulus-porosity trends and their lithology. Only small percentages of secondary minerals (dolomite and anhydrite) appear necessary to alter the rocks properties significantly. Poisson's ratio is less sensitive to lithology but correlates with porosity. The dynamic Young's moduli are higher than the static values but dynamic and static Poisson's ratios correlate well with each other for liquid saturated samples.
Dynamic to static transforms based on lithofacies were developed from these data to correct the acoustic log derived mechanical properties to static values appropriate for reservoir deformations. The corrected mechanical properties along with the trends observed between mechanical properties, lithofacies, and porosity allow for the design of more effective hydraulic fracture treatments by utilizing accurate values for the reservoir's mechanical properties and their variability.
