Promises and Pitfalls: Acoustic Properties in Carbonate Rocks

The acoustic properties of the matrix in carbonate rocks are affected by three main factors: pore fluids, rock framework and pore space configuration. In carbonate rocks, the latter two factors are a function of the depositional environment and the diagenetic history. Cementation, recrystallisation and dissolution processes can change the mineralogy and texture of the original framework and thereby alter the original grain-to-grain contacts and/or occlude pore space. Dissolution processes can enlarge interparticle pore space or dissolve grains entirely, thereby increasing porosity. Ultrasonic measurements of core plugs show that these diagenetic alterations and associated changes in the rock frame and pore structure result in a wide range of p-wave velocity at a given porosity. Understanding the effect of pore types on acoustic properties of carbonate rocks is vital for reliable porosity determination from seismic signatures. In addition, I will point out some pitfalls in relating pore type effects to observed acoustic properties responses.