Filtration properties of water based drilling fluids
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.