BAKER HUGHES - Drilling Fluids Reference Manual

RESERVOIR APPLICATION FLUIDS
Clays have very low porosity due to packing or compaction. Dewatering due to compaction,
overburden (weight) increase, and dehydration, will cause a rapid decrease in porosity. Below
6,000 feet, porosity decreases more slowly and is lost due to the re-crystallization of minerals in the
pore spaces.
Reservoir Fluids
A key to the analysis of reservoir performance and production are the physical properties of the
reservoir fluids, and the variation of these fluids during the recovery and exploitation phase.
Petroleum fluids are a complex of naturally occurring hydrocarbon compounds within the porous
rock or reservoir.
These fluids may occur as vapor, liquids or solids, or any combination thereof. Their fluid state in
the reservoir is a function of the temperature and pressure under which they exist. The chemical
composition of petroleum deposits varies widely, but they have one thing in common, they are all
predominantly composed of hydrogen (H) and carbon (C) with lesser quantities of sulfur (S),
nitrogen (N) and oxygen (O). Broken down, most petroleum deposits exhibit the following
composition:
C = 84 - 87%
H = 11 - 14%
S, N, O = 0.1 – 2%
The production or producibility of petroleum reservoirs depends upon the physical characteristics
of the fluid within the reservoir. Of primary importance are the fluid viscosity and density, or when
vapor and liquid exist, the relative viscosity and density of the mixture. Of equal importance are the
volumetric variations of the fluids related to temperature and pressure. These values usually vary
during reservoir depletion. Of great importance, therefore, is the correct and accurate sampling of
the reservoir fluid and the laboratory analysis of the sample before production.
Reservoir Fluid Types
Generally four types of fluids exist:
1. Normal Crudes – These are the hydrocarbon liquids present in the reservoir commonly called
“crude oil”. The viscosity of these liquids can be as low as 1 cp or as high as 1000 cp or above.
Specific gravity can vary from 0.825 up to 1.075, and color varies from amber to greenish
black. Volumetric characteristics are related to pressure of the reservoir and can be
demonstrated with the cell test.
Figure 6 - 4
Normal Crude Oil
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 6-6