Distinct Petro-acoustic signature for sonic-derived porosity prediction in dolostones

Dolomite reservoirs host significant volume of world’s hydrocarbons. Understanding the porosity distribution within such strata is crucial for hydrocarbon exploration. In this study, 100 dolomite samples were collected from Saudi Arabia to investigate the main controlling factors on sonic velocity, and to examine the application of porosity prediction from acoustic impedance (P-impedance).

Collected samples were plugged for porosity and velocity measurements. Thin-section were prepared from each sample to define the texture and pore types. Acoustic impedances were calculated using compressional velocity and bulk density.

The petrographic analysis revealed that the studied samples could be separated into two main groups Fabric-preserving dolostones, and Non-fabric preserving dolostones. In addition, pore type is the main controlling factor on the sonic velocity and consequently on the calculated acoustic impedances. The porosity-impedance relation reveals that the two groups could be separated at porosity higher than 10%. Each group showed distinct porosity-impedance trend characterized by high correlation (R2> 0.94). The fabric-preserving dolostones show higher impedances than non-fabric preserving dolostones. This is mainly due to the dominance of stiffer pores within the fabric-preserving dolostones, compared to less stiff pores within the non-fabric preserving dolostones. The results of this study can enhance the porosity prediction in dolostone strata.