Fluid Identification - Cased-Hole Log Analysis and Reservoir Performance Monitoring - page 96

Optical Fluid Density
Yet another way to distinguish between water, oil, and gas is by use of the measure-
ment of the optical fluid density. A light source provides beams of light at different
frequencies or colors, some in the visible spectrum and others in the near infrared.
The percentage of the incident light that passes through a known thickness of the
fluid being sampled is characteristic of the fluid involved. This technology is used
in open-hole wireline formation testers to determine what fluid is being pumped out
of the formation under test and is useful in that application to indicate to the opera-
tor when the initial flow of mud filtrate has been exhausted and the virgin formation
fluids are then flowing into the sample chamber. In production logging, the same
technology can be applied to distinguish the components of a flow stream in a well.
Figure 7.14 shows a schematic of the optical fluid analysis device and Fig. 7.15 the
optical fluid density of a number of fluids as a function of the wavelength of the
light employed.
Fig. 7.14 Optical fluid analysis device. Image copyright Schlumberger. Used with permission