Study On High Performance Drilling Fluid System And Its Application Prospect In Indonesia Demonstration Mining Area

With the development of geological drilling to deep strata,the complexity of strata increases significantly.The problems of lost circulation,sticking and wellbore instability are prominent,which cause huge economic losses and seriously hinder the development of geological drilling technology.Hydration expansion of shale is one of the most important reasons for wellbore instability.Therefore,the drilling fluid is required to have excellent inhibitive property.Because of the narrow annulus in geological drilling,the drilling fluid is required to have low viscosity and yield point.At present,the drilling fluid system has high viscosity and yield point and insufficient inhibitive property.It is difficult to meet the requirements of drilling technology.Therefore,the study of high performance drilling fluid system（low viscosity,low filtration,strong inhibition,good lubricity）has become a key technology urgently needed in modern geological coring drilling.Most of rocks in Indonesia Nabire gold mining area are magmatic rocks and some metamorphic rocks.Most rock samples have undergone alteration,resulting in loose and fragmented rocks.Meanwhile,rock cracks are well developed and rock brittleness is high.Therefore,drilling fluid is required to have excellent sealing,inhibition,anti-collapse and lubrication properties.Based on the lithologic characteristics and technical requirements of Nabire Gold Mine,Indonesia,this paper screened drilling fluid addictives by single factor optimization experiment and established drilling fluid systems by orthogonal experiment of four factors and three levels.Finally,three drilling fluid systems with temperature resistance of 70℃,low viscosity and yield point,low filtration and strong inhibition were established.The rheological properties at room temperature and high temperature/high pressure,filtration,inhibition and lubricity of the optimized drilling fluid systems were evaluated.The results of optimization and evaluation are as follows:1.Clay free weak gel drilling fluid system:water+0.1%NaOH+0.15%Na₂CO₃+0.5%XG+1.0%GCMS-7#+1.5%HPA+0.7%RHJ-1+5%KCl+0.07%1227+4%ultra-fine CaCO₃+0.1%RHPT-2.The apparent viscosity（AV）was 19.5 mPa·s,the plastic viscosity（PV）was 11 mPa·s,the yield point（YP）was 8.5 Pa,the YP/PV was0.77 Pa/mPa·s,and the FL_API was 7.2 mL.In the optimum formulation,the linear expansion rate of sodium bentonite after 16 h was 20.09%,the EP lubrication coefficient was 0.18,and the friction coefficient of mud cake was 0.12.2.Cationic emulsion polymer drilling fluid system:3%sodium bentonite+0.2%Na₂CO₃+0.3%DS-301+2.0%KHm+0.6%NH₄-HPAN+0.6%DS-302+0.5%RHJ-1+0.5%RHJ-3+0.5%HPA+5%ultra-fine CaCO3.The apparent viscosity（AV）was 10.5 mPa·s,the plastic viscosity（PV）was 8 mPa·s,the yield point（YP）was 2.5Pa,the YP/PV was 0.31 Pa/mPa·s,and the FL_API was 7.4 mL.In the optimum formulation,the linear expansion rate of sodium bentonite after 16 h was 13.49%,the EP lubrication coefficient was 0.24,and the friction coefficient of mud cake was 0.39.3.Calcium chloride drilling fluid system:22.5%CaCl₂+0.3%XG+3.0%fluid loss additive+2.25%ultra-fine CaCO₃+1.0%lubricant.The apparent viscosity（AV）was 32.5 mPa·s,the plastic viscosity（PV）was 21 mPa·s,the yield point（YP）was11.5 Pa,the YP/PV was 0.55 Pa/mPa·s,and the FL_API was 3.8 mL.In the optimum formulation,the linear expansion rate of sodium bentonite after 16 h was 2.88%,the EP lubrication coefficient was 0.05,and the friction coefficient of mud cake was 0.06.