Filtration properties of water based drilling fluids
Abstract
This thesis reports an experimental and theoretical study on filtration properties of
water based drilling fluids under dynamic and static conditions. The tested muds cover
Freshwater/Gypsum/Lignosulphonate mud and SeawaterlKCLlPolymer mud, bariteweighted
and unweighted. The effects of the solid concentration, pressure and shear rate
on the filter cake characteristics and the erodability were investigated. For static filtration
experiments, all tests were conducted for two hours and the spurt loss, the filter cake
thickness, the ratio of wet to dry cake mass and the cumulative filtrate volume against
time were measured. For dynamic filtration experiments, however, only the spurt loss
and the cumulative filtrate volume against time were measured and all tests were
conducted for at least 8 hours. A general filtration equation was developed based on the
cake filtration theory prevailing in the chemical engineering industry and it was utilised to
obtain the modified classic static filtration equation and the dynamic filtration equation.
The modified classic static filtration equation was then employed to fit the static filtration
experimental data and the average specific static cake resistance and the effective filter
medium resistance were calculated. The dynamic filtration equation showed a substantial
agreement with the dynamic filtration experimental data. Using the static filter cake
properties such as the ratio of wet to dry cake mass (m), the average specific dynamic
cake resistance, the effective filter medium resistance and the dynamic filter cake
erodability were calculated. In the study of the relationship between the static filtration
data and the dynamic filtration data, an attempt of predicting the dynamic filtration data
from the static filtration experimental data was conducted. Also, an attempt was carried
out to predict the static filtration data and the dynamic filtration data in a sequential
process. The experimental data suggests that a substantial difference exists between the specific resistances of static and dynamic filter cakes. No apparent distinction was found, however, between spurt loss and effective filter medium resistance. The reodability of dynamically deposited mud cake for Seawater/KCL/Polymer mud was found to be three fold for Freshwater/Gypsum/Lignosulphonate.