Abstract
The behavior of compressional or P-wave velocity passing through natural porous rocks with heterogeneous and irregular shapes of the pore system is not well understood. The present study implemented a modified Kozeny equation to characterize pore attributes, pore geometry and structure, in an attempt to investigate factors influencing the velocity. This equation is in the form of a power law one from which a concept of similarity in pore attributes can be derived. Employing a large number of data of porous sandstones, the results show that a similarity in the pore attribute plays an important role in relating the velocity with the details of geometry and structure of the pores system. For a given group of rocks having similar pore structure, an increase in the pore geometry variable, (k/f)0.5, tends to increase the velocity provided that the increase in the geometry is due to an increase in permeability followed by a decrease in porosity. Overall, the prediction of P-wave velocity is best obtained when the rocks are grouped according to pore structure similarity.
Highlights
The main problem of defining the relation of wave velocity of porous rocks with petrophysical properties is that the heterogeneities of rocks are closely associated with the geological processes that formed the rocks
Variations in the geological processes associated with the deposition and diagenetic process control the rock texture, the type of minerals, and clay content which in turn affects the size, shape and relationships or connectivity between the pores
The present study focuses on dry P-wave velocity measured on sandstone core plugs of various both pore geometries and pore structures
Summary
The main problem of defining the relation of wave velocity of porous rocks with petrophysical properties is that the heterogeneities of rocks are closely associated with the geological processes that formed the rocks. Variations in the geological processes associated with the deposition and diagenetic process control the rock texture (grain size, uniformity of grain size and grain arrangement), the type of minerals, and clay content which in turn affects the size, shape and relationships or connectivity between the pores. Content, shape, and composition of the material produce different grain distributions so that the geometry and pore structure are different. The value of critical porosity of a porous rock is determined by its common mineralogy, grain sorting and angularity, and subsequent diagenetic processes after deposition (Mavko et al, 2009). The use of knowing the critical velocity of a group of rocks is to obtain a better relation between the wave velocity and porosity
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