Formation Density Log Applications in Liquid-Filled Holes

Abstract

The formation density logging tool provides a radioactivity measurement that yields formation densities in situ.The relationship between bulk density and porosity is well understood. With knowledge of grain 'and fluid densities, porosity may be computed from the indicated formation bulk densities in shale-free formations. The porosities thus determined may be used with a resistivity log for water-saturation determinations. One technique utilizes a density vs resistivity plot.A plot of density vs Sonic-log transit time is used for porosity determinations in shaly sands. This method is particularly suited to wells drilled with oil-base or salt muds.In shale-free formations, comparisons of density values and neutron-log readings are used to identify lithology and, thus, to select appropriate values of grain density for porosity computations.Through the use of Formation Density, Sonic and neutron logs, the interpretation problems caused by complex matrix lithologies are simplified.Other applications of the Formation Density log are found in the identification of minerals in evaporite deposits and in yield determinations of "oil shales".

A Comparison of Shaly-Sand Interpretation Techniques in the Mesaverde Group of the Uinta Basin, Utah

“…This model was used in early computer applications in the field. Sw from the Simandoux relation in a practical form 16 The total shale relation, 16 or modified Simandoux equation,2 is described by the following: (17) and €/>a-€/>p q = -- (18) …”

Openhole Crossplot Concepts A Powerful Technique in Well Log Analysis

“…5) correlating log-derived parameters -such as the q factor [q = (<<1> AC -«1> DEN )/ «1> AC 1 , effective and total porosity, and production test data -has been developed for several geological provinces. 7,8 The DEN/ AC crossplot also has been proposed for refined, log-derived overpressure evaluation in the North Sea area. 9 Presence of mica (Pma ~3.1 g/cm3, f1tma = 64 J.l.s/ft), which is encountered in the massive Jurassic North Sea sands, is evident on the DEN/ AC crossplot (Fig.…”

New Analytical Method To Calculate Matrix- and Fluid-Corrected Total Porosity in Organic Shale

“…Compensated neutron tools use the ratio of detector count rates to minimize environmental effects (Alger et al 1972). Count rates or count-rate ratios are correlated to laboratory measurements performed on homogeneous, water-saturated blocks (usually limestone solid composition) with different porosities.…”

“…Nonetheless, this tool response is not totally disadvantageous. Low readings of neutron porosity compared with density porosity are used to qualitatively identify rock formations bearing gas or light oil (Alger et al 1972). In the case of hydrocarbon-rich shaly formations, the effect of gas and shale is opposite and results in neutron-porosity measurements that are often difficult to interpret.…”

“…Minerals such as anhydrite and gypsum have measurable effects on thermal-neutron logs caused by the presence of chemically attached water molecules that also lead to overestimation of neutron porosity (Savre 1963). Assuming water saturation in the calculation of porosity from neutron and density measurements can lead to errors of approximately 10% in the case of oil-bearing, and as high as 40% in the case of gas-bearing rocks (Alger et al 1963). An important breakthrough concerning the correction of neutron-porosity logs for presence of hydrocarbon in a clean matrix was proposed by Gaymard and Poupon (1968).…”