Core Analysis

Abstract

Core analysis is a recent development in the field of petroleum technology.The earliest work on this subject was done in connection with evaluating andplanning secondary oil recovery by water-flooding. Present-day analysis ofsands of flush fields requires new and independent interpretations of the dataprovided by cored material. Particular attention is being paid to thedevelopment of rapid, routine methods for measuring physical characteristics ofsandstone, such as permeability, porosity and grain size, as well as the sand's fluid content.Permeability may be defined as the fluid-passing capacity of a rock.For a sandstone to be permeable it must be possible to pass a measurablequantity of fluid through the material in a finite period of time. The commonunit of permeability is the darcy, which may be defined as the rate of viscousflow, in milliliters per second, of a fluid of one centipoise viscosity througha porous medium having a cross section of one square centimeter, under apressure gradient of one atmosphere (76.0 cm. Hg) per centimeter. 1 Forconvenience the subunit millidarcy, or one-thousandth darcy, is often used.Porosity is defined as the fluid-containing capacity of a rock and is usuallyexpressed as a percentage ratio of the total pore volume to the rock or bulkvolume. Since measurement of only the effective or communicating pore volume isoften made, porosities are distinguished as total or effective. Net effectiveporosity is defined as the net pore volume available for oil and gas. Oil andwater content of sand is measured and expressed either as the percentagesaturation of the total pores or of the bulk rock. The oil content may also beexpressed as the percentage saturation of the net effective pores.In connection with water-flooding, methods of core analysis were developed tofurnish data that could be used in determining the quantity of recoverable oil, and the probable rates at which various sands or divisions of a sand open tothe wells would take water or produce oil. In flush fields, the analytical dataare used to predict the productivity of a cored interval.T.P. 1024