The Effects of Rock Texture and Pore Type on Sonic Velocity in Dolomite

Shouwen Shen¹* and Gregor P. Eberli^2
1Saudi Aramco
²University of Miami, USA
*[email protected]

In order to assess the controlling parameters for velocity in dolomites, the sonic velocities of 129 dolomite samples with different porosities were measured and their petrologic textures were determined using microscopy. The results revealed that sonic velocity is a function not only of total porosity but also of the pore type and rock texture. The measured velocities showed an inverse correlation with porosity, but departures from the general trends of correlation can be as high as 1,500 meter/second. These deviations can be explained by the occurrence of different crystal shapes, pore type, rock type and crystal size. When crystal shape and pore type were combined to classify the dolomite many relationships became apparent. Seven texture combination types were distinguished in the study samples. Rocks with texture combinations of anhedral and moldic (A + M) have relatively high velocities, whereas those with mostly euhedral shapes and inter-crystalline pore types (E + I) have relative low velocities. Rock types partially explained the variations of velocities. Generally, grainstones have relatively high velocities, whereas mudstones have relative low ones. Breccias have the lowest velocities. Crystal size itself is very poorly correlated to sonic velocity except that large crystal sizes do not have slow velocities. However, if the crystal size of each combination-type is evaluated, the correlation improves. Because total porosity, together with pore type and rock texture, control sonic velocity in dolomite, it is possible to predict the velocity from these parameters. The highlight of this research is an empirical formula that predicts the velocity of dolomite.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain