Openhole Crossplot Concepts A Powerful Technique in Well Log Analysis

Abstract

A multitude of crossplot concepts for well logging parameters is available to the formation evaluation specialist. Raw and/or calculated logging parameters can be crossplotted on linear, semilogarithmic, and other exponential scales. Input data include resistivity, acoustic, and nuclear logging measurements and, if available, core, test, and production data. Applications of specific crossplot concepts allow recognition of log calibration problems, normalization of basic log measurements, and determination of lithologic reservoir characteristics in clastic and complex mineralogy. Additional information includes primary and total porosity, formation-water salinity, distinction between oil and gas, estimation of reservoir grain sizes, prediction of irreducible water saturation and, hence, anticipated water cut, heavy mineral analysis, and other data. This discussion focuses on advantages and limitations experienced with numerous crossplot techniques. Frequent reference is made to formation evaluation problems encountered in the North Sea area.

New techniques in lithofacies determination and permeability prediction in carbonates using well logs

“…Digitized logging parameters for each Resistivity crossplot from logs from the West Seminole Field where R t is the true resistivity, Rxo is the resistivity in the flushed zone, Rmf is the mud filtrate resistivity, R~ is the shallow laterolog resistivity and Rz is the estimated resistivity of mud filtrate and formation water in the partially flushed zonc. facies were then crossplotted following the method of Fertl (1981), and it was found that a plot of R t against q~p (Fig. 3) as well as a plot of ~o_ R t against q~N, could be used to distinguish the various facies.…”

Investigation of Petrophysical Parameters of Kangan Reservoir Formation in One of the Iran South Hydrocarbon Fields

“…Thus according to the following equations, the nominal porosity determined through density log is Open Journal of Yangtze Gas and Oil calculated and its shale effect is eliminated [12]. ma log Da ma fl ρ ρ φ ρ ρ − = − (11) φ Da is the nominal porosity read from density log, ρ ma is matrix density and ρ fl is the fluid density. In the next step, nominal porosity (φ Da ) affected by shale is corrected using the following equation [12].…”

“…The amount of porosity is obtained by Equation (2) in which φ is real porosity, a and b are experimental constant values and N is the value of used tools [11].…”

“…In non-shale formations (clean), porosity is calculated by density logging through Equation (3) [11]. According to this equation, matrix and density of the fluid determine porosity.…”

“…Comparing neutron with density double logging, the result indicates that the presence of gas can separate these two logs which are called the effect of rotor. Using Equation (8), the porosity is calculated through neutron-density crossplot [11] (Fertle et al, 1987).…”