NH_4Ca(NO_3)_3内相油基钻井液性能探讨

Properties of Oil-Based Drilling Fluid with NH_4Ca(NO_3)_3 as Internal Salt

分别以CaCl2、HCOOK、HCOONa和NH4Ca(NO3)3为内相,配制具有相同活度(0.9)、相同密度(1.8 g/cm3)的油基钻井液体系,油水体积比为80∶20。比较了4种钻井液的流变性、动态/静态沉降性能、黏弹性、触变性,考察了NH4Ca(NO3)3钻井液的抗污染能力。结果表明,150℃滚动老化16 h后,相同剪切速率下,NH4Ca(NO3)3内相油基钻井液体系剪切应力最小,黏度最低。在50℃、170.3 s-1下,该体系密度降低了0.255 g/cm3,其他3种钻井液的密度降低值⊿ρ为0.513~0.545 g/cm3;相同剪切应力下,NH4Ca(NO3)3钻井液弹性模量和黏性模量的比值(G’/G’’)最大,体系动态沉降稳定性能最好。在10000 r/min下搅拌30 min后在50℃静置16 h,NH4Ca(NO3)3钻井液体系的表面张力为27.744 mN/m2,上层分离油体积为1.37 mL,剩余溶液的上下层密度差为0.038 g/cm3;该体系的凝胶尖峰为3.47 Pa,静态沉降稳定性和触变性最好。NH4Ca(NO3)3钻井液体系抗污染能力较强,可以抗10%劣土污染和15%盐水侵入污染。

The oil-based drilling fluid with same water activity(0.9),density(ρ=1.8 g/cm3)and oil-water volume ratio(80∶20)composed by different internal salt such as CaCl2,HCOOK,HCOONa and NH4Ca(NO3)3 was formulated indoors. The rehological property,dynamic/static settling stability,viscoelastic property and thixotropic ability of four different systems were compared and the anti-pollution ability of NH4Ca(NO3)3 internal oil-based drilling fluid was studied. The results showed that after the systems were aged under the temperature of 150℃ for 16 h,NH4Ca(NO3)3 drilling fluid had the lowest shear force under the same shear rate compared with other drilling fluids with the lowest viscosity. The density decrease of NH4Ca(NO3)3 drilling fluid was only 0.255 g/cm3,while the ⊿ρ of other internal salt drilling fluids were 0.513—0.545 g/cm3 under the shear rate of 170.3 s-1 at 50℃. The ratio of elastic modulus and viscosity modulus(G' /G'')of NH4Ca(NO3)3 drilling fluid was the highest among four systems,which showed that it had the best dynamic settling stability. When four drilling fluids were aged at 50℃ for 16 h after they were sheared under the shear rate of 10000 r/min for 30 min at 50℃,the surface tension of NH4Ca(NO3)3 drilling fluid was 27.744 mN/m,the free oil volume was the smallest with only 1.37 mL and the density difference of upper and lower for the residual solution was only 0.038 g/cm3. It could formed the strongest gel structure with the peak of gel was 3.47 Pa. NH4Ca(NO3)3 drilling fluid had the best static settling stability and thixotropic ability. 10% drilling solids and 15% salt water were added to the system to test the effect of drill solids and brine on the property. The result showed that NH4Ca(NO3)3 drilling fluid had good anti-pollution performance.