INTRODUCTION

The most basic property of reservoir rocks is porosity (f) which allows the rock to store fluids (gas, oil, and water). The total volume of fluid that can be stored in a given bulk volume (V _b) of rock is its pore volume (V _p). The solids volume (or grain volume) (V _s), is the portion of the rock comprised only of solid matter. The total exterior, or bulk volume, of the rock is, therefore, the sum of the grain and pore volumes. The total, or absolute porosity, is the pore volume divided by the bulk volume (expressed as percentage, or fraction, of the bulk volume). The void ratio (e) is the pore volume divided by the solids volume.

The complex internal structure of pores and solution vugs in rocks frequently results in the formation of isolated pores. These isolated pores contribute to the overall (or absolute) porosity of the rock, but are not interconnected to the main body of pores and, therefore, are not involved in the flow of fluids through the rock. The interconnected pores that support the flow of fluids make up the effective porosity, which is numerically less than the absolute porosity, that is, the intercommunicating porosity excluding the pores containing irreducible fluid saturation. The small pores occupied by the irreducible fluid (water or oil), and cracks and dead-end pores are not involved in the flow process.

For example: the mass (M) of a sample...