Acoustic Properties of Continental Carbonate Rocks - Controlling Factors, Analytical and Numerical Simulations

The complex nature of carbonate rocks is a major challenge when interpreting seismic data for subsurface characterization. Understanding the relations between sonic velocity and carbonate rock type is one of the keys to interpret data from seismic sections or from acoustic logs. Studies have shown that elastic properties of carbonate rocks are affected by many parameters such as dominant mineralogy, rock fabric, pore type and shape, porosity, and pore fluid, making it difficult to attribute changes in seismic expression to any one parameter. Continental carbonates gained interest following the discovery of the supergiant field in the post- and pre-salt deposits in offshore Brazil, as they account for a large portion of the deepwater production. The genesis of continental carbonates is generally associated with physico-chemical and biological precipitation of carbonates, coupled with a strong influence of clastic mineralogical inputs. This results in a complex mineralogical mixing, associated with a wide heterogeneity of pore types due to the intense diagenetic overprint potential of carbonate deposits (cementation, dissolution, recrystallisation, dolomitisation...). With that in mind, we propose insights on the controling factors of elastic properties in a continental carbonate dataset, analogue of the brazilian pre-salt deposits. An applicable model based on the effective medium theory is proposed and discussed regarding the experimental results, and try to account for the wide variability of the elastic properties. In addition, a numerical estimation of elastic properties is carried out on virtual microstructures generated by a random sequential addition (RSA) algorithm.