Petroleum Reservoir Engineering Practice: Porosity of Reservoir Rocks
Porosity is defined as a measure of the capacity of reservoir rocks to contain or store fluids. The fluids stored in the pore spaces within the reservoir rocks could be gas, oil, and water. High porosity values indicate high capacities of the reservoir rocks to contain these fluids, while low porosity values indicate the opposite. Consequently, porosity data are routinely used qualitatively and quantitatively to assess and estimate the potential volume of hydrocarbons contained in a reservoir. For instance, in a discovery well that shows the presence of hydrocarbons in the reservoir rocks, the set of data that is reviewed at least qualitatively to evaluate reservoir potential is porosity data acquired with either logging-while-drilling (LWD) tools or by running wireline tools. Porosity data are obtained from direct measurements on core samples and/or indirectly from well logs. In most cases, porosity data from core samples are used to validate or calibrate porosity data from well logs. Porosity data are also used in reservoir characterization for the classification of lithological facies, and the assignment of permeabilities using porosity-permeability transforms. Since porosity data are very important in many reservoir engineering calculations, this book begins by reviewing basic concepts in the determination of rock porosities. This review is concise and serves to refresh the reader with the many sources of porosity data that exist through applications of different formation evaluation tools.