Low Speed Ladder Drilling Fluid Rheology And Thixotropy

The thixotropy is one of the most important characteristics of the drilling fluid. The low-speed gradient drilling fluid's thixotropy means the thixotropy of the drilling fluid at the low shear rate.In process of oil drilling,the drilling fluid needs good rheology and thixotropy.At the moment of starting and stopping the mud pump,and up recurrent carrying sediment flowing in the annular space,and seepage flowing in the thief layer,the drilling fluid running very slowly.Right now the thixotropy of the drilling fluid is titled as the low-speed gradient thixotropy.Studying on the low-speed gradient drilling fluid's thixotropy is a very important scientific foundation on the evaluating the capacity of the drilling fluid carrying and suspending drilling cutting, stabilizing borehole and balance the formation pressure.This paper chose LV—CMC,FA367,PAC141,80A51,tri-sulfonated and polymer sulfonated drilling fluid system as experiment reagent.Through change the content and species of the treating agent,testing these systems'rheology and thixotropy at the regular speed gradient and low-speed gradient.Chose Znn-D6 six-rotating-speed rotational viscometer test these drilling fluid systems' rheology and thixotropy.Get the rheological parameters in the range of 5.11s^-1～1022s^-1,and draw out the thixotropy-loop.According to the thixotropy-loop,we can see every drilling fluid system has thixotropy.With the content of the treating agent increased, systems'thixotropy are increased,rheological parameters are higher,and shear stress are increased.Chose Znn-D6 six-rotating-speed rotational viscometer in the range of 5.11s^-1～1022s^-1 test.According to the relationship of the viscosity and shear stress with the shear rate,get the thixotropy equation about rheological index n and consistency coefficient K in this range of the shear rate.After sheafing all of systems,standing 10s and 10min to 1 hour,then test the shear stress.And regression fitting,get out the time-thixotropy equation with the standing time.The paper emphasis on using DV-Ⅲrheometer test the rheology and thixotropy of these drilling fluid systems at the extremely low- speed gradient.The speed gradient is low to 0.1～10s^-1.Through testing these drilling fluid systems' rheology and thixotropy at the low-speed gradient,drawing out the relationship curve about the viscosity- shear rate.The paper analysised the influence of the treating kind and agent and systems' temperature and the time of shear stress on these drilling fluid systems at the low-speed gradient.And using least square method fitting the experimental data,get out the thixotropy equation based on the hear rate,temperature and shear stress time.The paper discussed the evaluation method of the basic rheology and thixotropy of the drilling fluid systems.The paper also obtained the rheological equation of the drilling fluid systems in rectangular coordinate system,cylindrical coordinate system and spherical coordinate system.Combinning with the experiment at regular-speed gradient and low-speed gradient,analysised the rheology rule of the drilling fluid at circular tube and annular space in low low-speed gradient.At last the paper gave the rheological parameters' expression of all kinds of fluid.