Changes

===Density logging===

===Density logging===

Borehole gravity density measurements are unhindered by casing, poor hole conditions, and all but the deepest fluid invasion. The BHGM measurement samples a large volume of rock, which provides a density-porosity value that is more representative of the formation. This is especially beneficial in carbonate and fractured reservoirs.<ref name=pt07r48>Rasmussen, N. F., 1975, The successful use of the borehole gravity meter in Northern Michigan: The Log Analyst, v. 16, n. 5, p. 3–10.</ref> BHGM surveys have been used to find hydrocarbon-filled porosity missed by other logs in both open and cased holes. Gas-saturated sands are a particularly easy target<ref name=pt07r16>Gournay, L. S., Maute, R. E., 1982, Detection of bypassed gas using borehole gravimeter and pulsed neutron capture logs: The Log Analyst, v. 23, n. 3, p. 27–32.</ref>.

Borehole gravity density measurements are unhindered by casing, poor hole conditions, and all but the deepest fluid invasion. The BHGM measurement samples a large volume of rock, which provides a density-porosity value that is more representative of the formation. This is especially beneficial in carbonate and fractured reservoirs.<ref name=pt07r48>Rasmussen, N. F., 1975, The successful use of the borehole gravity meter in Northern Michigan: The Log Analyst, v. 16, n. 5, p. 3–10.</ref> BHGM surveys have been used to find hydrocarbon-filled porosity missed by other logs in both open and cased holes. Gas-saturated sands are a particularly easy target.<ref name=pt07r16>Gournay, L. S., Maute, R. E., 1982, Detection of bypassed gas using borehole gravimeter and pulsed neutron capture logs: The Log Analyst, v. 23, n. 3, p. 27–32.</ref>

The wide radius of investigation has also been successfully used to determine gas-oil and oil-water contacts in reservoirs where other measurements have been ineffective.<ref name=pt07r60>van Popta, J., 1990, Use of Borehole gravimetry for reservoir characterization and fluid saturation monitoring: Society of Petroleum Engineers, SPE 20896.</ref><ref name=pt07r51>Schultz, A. K., 1989, Monitoring fluid movement with the Borehole gravity meter: Geophysics, v. 54, n. 10., p. 1267–1273., 10., 1190/1., 1442586</ref> BHGM density measurements have been used to calculate hydrocarbon saturations: the larger the fluid density contrast, the larger the measured effect. Gas saturations are therefore the easiest to measure. The difference in densities measured by the gamma-gamma log and the BHGM can be used to calculate the difference in oil saturation between the invaded and undisturbed zones, which can in turn give an estimate of movable hydrocarbons.

The wide radius of investigation has also been successfully used to determine gas-oil and oil-water contacts in reservoirs where other measurements have been ineffective.<ref name=pt07r60>van Popta, J., 1990, Use of Borehole gravimetry for reservoir characterization and fluid saturation monitoring: Society of Petroleum Engineers, SPE 20896.</ref><ref name=pt07r51>Schultz, A. K., 1989, Monitoring fluid movement with the Borehole gravity meter: Geophysics, v. 54, n. 10., p. 1267–1273., 10., 1190/1., 1442586</ref> BHGM density measurements have been used to calculate hydrocarbon saturations: the larger the fluid density contrast, the larger the measured effect. Gas saturations are therefore the easiest to measure. The difference in densities measured by the gamma-gamma log and the BHGM can be used to calculate the difference in oil saturation between the invaded and undisturbed zones, which can in turn give an estimate of movable hydrocarbons.