The Litho-Porosity Cross Plot A Method Of Determining Rock Characteristics For Computation Of Log Data

Abstract

A common practice in log interpretation is to cross-plot van"ous porosity log readings in order to determine formation iithoiogy and compute porosi~accurately. LCrossplots of Sonic versus Densi~logs are widely used in the interpretation of shaly sands. For carbonates, Density versus Neutron cross-plots are commonly employed. These plots and the calculations based on them are extremely useful, but, when the lithology is a complex mtiture of ,m~",qg!$ i,nterpretgtie.~OJf the drta OJfte.nMcmnes am-bi~ous. The "Lithe-Porosity" cross-plot is introduced for interpretation in formations of complex lithology. It presents simultaneously the data from all three of the standard porosity tools: the Sidewall Neutron Porosity log, or the GNT; the Formation Density Compensated log; and the Borehole Compensated Sonic log. From the readings of these logs two porosity-independent parameters, "M" and "N'; are derived-M from the Sonic and Density, and N sented by a unique point regardless of porosity. For a formation of complex lithologv, the position of the log data points on the M-N plot relative to the pure mineral points is of great assistance in identifying various minerals in the formation. Litho!ogical information so derived is then used to calculate accurate values of porosity. The computer can be programmed to produce cross-plots of M versus N from logging data recorded on magnetic tape, or on punched cards. The method allows detailed studies of individual formations and compan"sons with other we[[s in a fraction of the time required using manual methods.The Lithe-Porosity technique has many applications in formation evaluation and interpretation. Examples are shown in the paper.

Lithology Investigation of Shaly Sand Reservoir by using Wire Line Data, “Nubian Sandstone” SE Sirt Basin

“…This technique is very similar to the previous one and introduced by Burke et al [1] for the study of complex lithologies. The authors apply this technique to compute parameters M and N independently of porosity assuming that all three tools (Neutron, Density and Sonic) respond linearly to porosity.…”

“…They allow measurement of apparent thickness and of real thickness if dipmeter data are taken into account. Burke et al and Clavier and Rust [1,2] have shown that well log responses can give a good idea of the lithology. With the increase of physical parameters recorded by modern logging tools e.g., parameters recorded by modern logging tools e.g., photoelectric cross section, natural or induced gamma ray photoelectric cross section, natural or induced gamma ray spectrometry (GRS), and dielectric constant it becomes more obvious that their combination can give a good lithologic description of the formations.…”

Rock Typing and Characterization of the Late Cretaceous Abu Roash "G" Reservoirs at East Alam El-Shawish Field, Western Desert, Egypt

“…M-N diagrams were employed to facilitate the interpretation of rocks based on neutron, density, and sonic logs. This chart, initially published by [43], utilizes three porosity logs to define the lithology-dependent quantities, M and N, which are independent of primary porosity. The M-N plot provides a clearer visualization of the lithological features.…”

Petrophysical analysis of regional-scale thermal properties for improved simulations of geothermal installations and basin-scale heat and fluid flow

“…If the number of components is larger than that, more measurements need to be taken into account and the analysis method needs to be changed. Burke et al (1969) developed the M-N plot, a method to analyse the mineral composition of a three-phase system. The original method uses sonic, neutron porosity, and density logs to compute two parameters M and N which are independent of porosity and can be used to identify the occurring minerals:…”