Research On Calcium Chloride And Clay-free Drilling Fluid System

With petroleum exploration and exploitation' deep development,deep and special process wells tend to be more and more.In the domestic and abroad,there are many special process wells of drilling,such as slimhole wells drilling,high temperature deep well drilling and highly-deviated well drilling and so on,which use more clay drilling fluid system containing bentonite to drill oil and gas layer.However,clay drilling fluid contains clay,fine clay particles,which get into reservoir easily,causing the hydrocarbon contamination.Therefore,it is vital important to study a kind of clay free drilling fluid system for the strong water sensitivity and strong stress mud page such as hydration expansion of the shale formation,which can effectively prevent the borehole wall collapse,create favorable conditions for improving the drilling rate and avoid the solid particle invasion formation for reservoir protection foundation.Through indoor research of clay-free drilling system in the study,it is concluded that a set of density in 1.16 ~ 1.77 g/cm~3 of calcium chloride clay-free drilling system is optimized by optimizing drilling fluid treatment agent,such as,viscosifiering and improving shear force agent,sealing polymer and reducing the fluid loss agent,inhibitor,and the various agents adding amount.Through the research of optimizing drilling fluid treatment agent and the optimization of the treatment agents added amount,we form calcium chloride clay-free drilling system formula that the resistance to calcium is 20% and the resistance to temperature is 150?.The clay-free drilling system performance evaluation results show that after 150?,16 hours high temperature aging,API filtration volume is 1.2 m L,high temperature and high pressure filtration volume is 14 mL,and the filter cake is thin and uniform after the API,high temperature and high pressure water loss test.The apparent viscosity of drilling fluid system was 48 mPa·s before aging,and the apparent viscosity of drilling fluid system was 49 mPa·s after aging.Before and after aging,the drilling fluid system's yield point and plastic viscosity ratio were 0.42Pa/mPa·s and 0.45 Pa/mPa·s;After 150?,16 hours high temperature aging,upper and bottom layers density difference of 1.24 g/cm~3 calcium chloride clay-free drilling system was 0 g/cm~3 after standing for 24 hours,and the upper and bottom layers density difference was 0.01 g/cm~3 after standing for 48 hours.In the shale rolling recovery experiments,the clay-free drilling system contains 20% calcium chloride,the shale recovery rate is as high as 95.1%,secondary recovery rate is as high as 92.2%,In drilling fluid lubrication performance experiments,under the condition of no added lubricant,different density of drilling fluid lubrication coefficients measured are: 0.1275,0.1259,0.1694.The results showed that the clay-free drilling fluid system has good filter loss property,rheological property,high temperature stability,anti collapse inhibition performance and lubrication performance.And Resistance capacity limit of bentonite pollution,water pollution and cuttings contamination can all reach more than 15%,which is suitable for borehole wall stability and reservoir protection.