The compressional sonic log can be used as a moderately good estimator of porosity in water and, to some degree, oil-filled rocks.

• Stratigraphic correlation. • Identification of compaction. The equation is the following: Where: ɸs= sonic porosity; Cp= compaction factor

Sonic Porosity- Unconsolidated Formations.

Using porosity logs.

• Identification of source rocks. The answer porosity will be too high in gas if the corrections are not made. Figure 5. • Determination of porosity (together with the FDC and CNL tools). The sonic porosity measurement (calculated using a limestone matrix value, 47.6 μsec/ft) is shown by a long dashed line on a scale ranging from −0.10 to 0.30 (−10% to 30%) increasing from right to left. Sonic Log Porosity from Hunt-Raymer Method (curved lines) and Wyllie Method (straight lines) - Shale Corrections Are Required Before Using This Graph. Thus, when the sonic porosity is less than some measurement of the total porosity, the difference can be attributed to the presence of post-depositional, or secondary, porosity. To calculate sonic porosity for unconsolidated formation, we can start by getting the product of the Wyllie et al.

Given the neutron porosity log and the densities of clay (2.68 g/cc) and shale (2.35 g/cc), the volume fraction of shale (Vsh NPHI) can be calculated via determination of the clay-bound water by setting values representative of clean sand and pure shale that correspond to the maximum and minimum value of the neutron porosity log, respectively. Gas corrections similar to those used in the Wyllie method can be used if needed.

It s also useful in the detection of gas-bearing formations and in the recognition of evaporites.

An equation relating acoustic travel time to the matrix and fluid times with the aim of quantifying sonic porosity in clean formations is introduced. The gas correction represents a 45 degree line (in porosity units) on the crossplot.

The tool works at a higher frequency than seismic waves, therefore one must be careful with the direct comparison and application of sonic … where DT is the compressional sonic transit time, DTma is the matrix transit time (54 us/ft for sandstone, 48 us/ft for limestone, 44 us/ft for dolomite), VSH is the shale fraction (next section) and c and d are fitting constants.

In general, the sonic log is unsuitable for these formations and should not be used to determine porosities.

Primary and secondary porosity The neutron and density logs are responses to pores of all sizes. An equation relating acoustic travel time to the matrix and fluid times with the aim of quantifying sonic porosity in clean formations is introduced. Sonic log interval transit time (DT) is represented by a solid line, on a scale ranging from 140 to 40 μsec/ft increasing from right to left. Effective porosity is most commonly considered to represent the porosity of a rock or sediment available to contribute to fluid flow through the rock or sediment, or often in terms of "flow to a borehole".Porosity that is not considered "effective porosity" includes water bound to clay particles (known as bound water) and isolated "vuggy" porosity (vugs not connected to other pores). Through sound wave we calculate the porosity. However, field observation over many years has shown that the sonic log is a measure of interparticle (intergranular and intercrystalline) porosity but is largely …

Contents Density predictions using Vp and Vs sonic logs CREWES Research Report — Volume 10 (1998) 10-5 Figure 4. Figure 5. The formula required to estimate the sonic porosity is: phiS = c.(DT - DTma)/DT - d.VSH. Using porosity logs. However, it depends upon the sonic travel time of pore fluid, which may be unknown if the fluid column is variable, or if there is a transition zone with a blend of fluids. 13. THE FORMATION DENSITY LOG 13.1 Introduction The formation density log measures the bulk density of the formation. Its main use is to derive a value for the total porosity of the formation.

The method is best used in carbonates with or without gas, and is inappropriate for shaly sand. Density (g/cm3) versus Vs (ft/s) for 09-17 well showing the best-fit line through the data.