Rheological Properties And Temperature Dependence Of Organoclay Suspensions For Oil-based Drilling Fluids

Because of its excellent lubricity,wellbore stability and high thermal stability,oil-based drilling fluids is widely used in the fields of offshore oil well and high temperature well.organoclay is often used for increasing viscosity and shear to suspend barite and carry drill cuttings.Its properties have a direct impact on the rock-carrying capacity of oil-based drilling fluids and the stability of borehole wall.There are many additives besides organoclay in the actual oil-base drilling fluids suspensions,such as wetting agent and emulsifier.As a dispersing agent,the wetting agent can make the hydrophilic barite and drill cuttings in the oil-based drilling fluids disperse and suspend well in the oil phase,and it is not easy to aggregate into pellets.However,wetting agent may be adsorbed to the surface of organoclay,which will affect the performance of the organoclay.Formation water also affects the performance of organoclay suspensions.The rheology of organoclay suspensions depend on temperature,and the viscosity increase with increasing temperature.In previous studies on the temperature dependence of organoclay suspension,the rheological properties of organoclay suspension were only tested at a fixed temperature after aging at different temperatures,without considering the real-time rheology of the system at different temperatures.In this thesis,the temperature dependence of organoclay suspensions after high temperature aging is determined by testing the corresponding rheological properties in a wide temperature range.This method can better represent the rheological properties of organoclay suspensions at different temperatures.Both the wetting agent used in oil-based drilling fluids and formation water in the drilling process may affect the performance of organoclay suspensions,and the rheology of organoclay suspension depends on temperature.In view of the above problems,the following work is carried out in this thesis:(1)In order to explore the influence of wetting agent on the performance of organoclay suspensions,the organoclay suspensions are prepared by in-situ modification of Namontmorillonite(Na-MMT)in isoparaffin(Isopar-M)with the cationic surfactant dimethyldioctadecylammonium chloride(ODMA).A dichain polyisobutylenesuccinimide(T154A)is used as wetting agent.The effects of T154A concentration,stirring time and other factors on the stability and rheological properties of organoclay suspensions,are investigated by optical microscope and rheometer.The results show that with the increase of T154A,the suspensions gradually change from a non-Newtonian fluid in shear dilution to a Newtonian fluid,which greatly reduces the viscosity and shear force of organoclay suspensions,resulting in the loss of rheological property.At 80℃,for the organoclay suspensions with T154A added,the viscosity and shear force gradually increase with the increase of stirring time,and the suspensions recover from Newtonian fluid to non-Newtonian fluid.In order to explore the influence of formation water on the performance of organoclay suspensions,different amounts of deionized water and 25 wt%CaCl2 brine are added to the suspensions.The effects of a small amount of water on the static stability,apparent viscosity and yield stress of the organoclay suspensions without 180℃ high temperature treatment and the organoclay suspensions after 180℃ high temperature treatment are investigated.The results show that deionized water increases the apparent viscosity and yield stress of the suspensions that do not undergo high-temperature treatment;and deionized water increases the yield stress of the suspensions that after high-temperature treatment,but has little effect on the apparent viscosity.25 wt%CaCl2 brine has little effect on the static stability and apparent viscosity of the organoclay suspensions without high temperature treatment and the organoclay suspensions after high temperature treatment,and increases the yield stress.These data provide a new idea for exploring the properties of organoclay for oil-based drilling increases.(2)In order to reduce the influence of temperature change on organoclay suspensions of ODMA modified,dodecyl polyoxyethylene ether dimethyl methyl ammonium chloride(EDMA)and dodecyl polyoxyethylene ether dimethyl dodecyl ammonium bromide(EDDA)are used to modify Na-montmorillonite in isoparaffin respectively to prepare organoclay suspensions.The influence of modifier type,particle concentration,modifier concentration and other factors on the temperature dependence of rheological properties of organoclay suspensions in the range of 5-120℃,as well as the temperature dependence of simulated oilbase drilling fluids prepared are investigated.The results show that the degree of temperature dependence of the apparent viscosity of organoclay suspensions is ODMA>EDDA>EDMA;the concentration of particles has no effect on the temperature dependence of the suspensions;the overall viscosity and temperature dependence of the suspensions increase with the increase of the concentration of the modifier.The temperature dependence of rheological properties of simulated oil-based drilling fluids prepared with EDMA modified organoclay are also lower.The exploration of reducing the temperature dependence of organoclay suspensions provides some help for the study of temperature resistance of organoclay.