Density Logging in the Gulf Coast Area
- John L.P. Campbell (Lane-Wells Co.) | John C. Wilson (Lane-Wells Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- July 1958
- Document Type
- Journal Paper
- 21 - 25
- 1958. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 1.6.9 Coring, Fishing, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 5.2.1 Phase Behavior and PVT Measurements, 5.2 Reservoir Fluid Dynamics, 2 Well Completion, 4.3.4 Scale, 5.5.2 Core Analysis, 4.1.2 Separation and Treating, 1.2.3 Rock properties, 2.4.3 Sand/Solids Control, 4.1.5 Processing Equipment, 5.6.1 Open hole/cased hole log analysis
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A radiation log, depending upon gamma rays scattered by and absorbed in the formation, gives a record from which the formation density can be derived. A comparison with laboratory measurements of cores sets the accuracy of the log at approximately 0.03 gm/cc.
In areas where lithological identification and correlation is difficult, the density log can give useful assistance.
The density log provides more representative and detailed density values for gravity meter interpretation than has been available from measurements made on either bit cuttings, well cores or outcrop samples.
Densities derived from the density log provide a means of calculating the formation porosity in limestone and sandstone reservoirs.
Well logging equipment has been developed for measuring and recording many properties of the rocks through which the borehole passes, which are useful in the solution of exploration, well completion and petroleum production problems. Rock density or weight per unit volume of rock is a very important and basic rock property which has never been fully exploited. This has been due principally to the difficulty in making a suitable measurement of formation density from the borehole. However, within the past few years application of the strong effect of the density of materials on the absorption of gamma rays passing through them has provided a reliable means of making a continuous well log of formation density.
The density of materials can be measured in pounds per cubic foot but the metric unit, grams per cubic centimeter, is more commonly used because it is numerically equal to the specific gravity of the material, that is, the number of times the material is heavier than the same volume of water. The density of a rock is dependent upon the minerals of which it is composed. It varies from a low of 1.30 for lignites, through 2.05 for sulfur, 2.15 for salt, 2.31 for gypsum, 2.65 for clean non-porous sandstones, 2.71 for limestone, 2.85 for pure dolomites and 2.92 for anhydrite. These densities may be used for lithological identification of rocks which are known to be pure and non-porous. Fig. 1 illustrates the correlation of two logs showing density difference lithologically. However, many of the sediments are heterogeneous mixtures and cannot be identified on the basis of density measurement alone.
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