BAKER HUGHES - Drilling Fluids Reference Manual

Hydraulics
The theoretical change in filtrate, due to reduction of the viscosity of the filtrate as temperature is
increased, can be expressed by the following equation:
where,
f 1 = f μ
× ---------
μ 1
f = filtrate at a known temperature
f l = filtrate at an elevated temperature
μ = viscosity of water at known temperature
μ 1 = viscosity of water at an elevated temperature
The change in viscosity for water at various temperatures is noted in Table 1-2.
Table 1-2 Viscosity of Water vs. Temperature
Temperature Viscosity of Water
(Centipoise)
Temperature Viscosity of Water
(Centipoise)
°C °F °C °F
0 32 1.792 40 104 0.656
10 50 1.308 60 140 0.469
20 68 1.005 80 176 0.356
30 86 0.801 100 212 0.284
(Data from Rogers, W. F.; Composition and Properties of Oil Well Drilling Fluids, Third Edition)
For example, a fluid has a known filtrate of 6.0 mL at 86°F and 100 psi. It is desired to predict the
resultant filtrate at 140°F with pressure constant.
f 1
f ---------
μ 0.801
= × = 6.0 × ----------------- = 6.0 ×
.895 --------- = 7.8
.469 .685
μ1
Temperature changes of water-base fluid in the 80° to 140°F range will result in change of filtrate of
approximately 10% for each 17°F change. Filtrate increases as temperature increases.
Viscosity
The viscosity of the fluid phase of the drilling fluid, which is the same as the viscosity of the filtrate,
has a direct influence upon the filtration rate. The viscosity of filtrate, which is directly affected by
temperature has been previously described. As the filtrate viscosity decreases, the filtration rate and
total volume of filtrate measured increases.
Filtrate viscosity is also affected by water soluble materials, particularly polymers. When polymers
are added to the mud system, the viscosity of the fluid phase as well as the whole mud is increased,
thereby reducing the filtration rate. The equations presented above may be used to predict the effects
of water soluble polymers on the filtration rate. One must know, or have measured, the effects of
polymer additions on the viscosity of the filtrate in order to make such predictions.
Reference Manual
Baker Hughes Drilling Fluids
1-24 Revised 2006