Optimization And Evaluation Of High Temperature And High Density Drilling Fluid System In Shunbei Area

There are abundant oil and gas resources in the Shuntuoguole area of the Tarim Basin in Xinjiang.The Shunbei area has complex topographical conditions,a series of fault zones,and deep oil and gas reservoirs.It has encountered many difficulties in the exploration and development of oil and gas:Mesozoic strata sand and mud stone interactions Layers are easy to leak and make slurry;the Paleozoic strata have developed cracks and pores,and the leakage is serious;the adjacent wells are invaded by salt water several times;the high temperature makes the rheology of the drilling fluid difficult to control and other problems.Through physical and chemical analysis and clay mineral content analysis of the Triassic Halahatang Formation and Ketur Formation shale in the Shunbei area of Triassic,the clay content of this formation is relatively high,among which the Halahatang Formation drill cuttings samples The clay content is high,the main mineral component is I/S,and the relative content is 80%;the clay content of the Kotul Formation is about 70%,and the main clay mineral components are chlorite and illite.Based on the geological conditions of the Shunbei industrial area,the high content of clay minerals,the development of micro-fractures,and the distribution of fracture zones are the reasons for the instability of the Shunbei shaft wall.Therefore,it is necessary to develop a simple,low-cost,high-performance drilling fluid system based on the characteristics of high temperature and high pressure in the Shunbei District.Sodium bentonite and attapulgite composite soil slurry with a ratio of 1:1 is used in the preparation of the base slurry,which can maintain a high slurry production rate at high temperatures;adding 15%NaCl and 5%KCl composite brine improves the resistance of the base slurry.Salt inhibition ability and density;then after selecting a series of main treatment agents such as:HPL-3,sulfonated lignite resin,emulsified asphalt,polyamine HPA,etc..In particular,the introduction of the new temperature and salt resistance polymer HPL-3 has a significant effect on reducing fluid loss at high temperatures.The drilling fluid formula is:water+1.5%sodium soil+1.5%attapulgite+0.3%Na₂CO₃+0.1%Na OH+15%NaCl+5%KCl+1.8%HPL-3+1.0%LV-PAC+4%SMC+6%SPNH+0.5%HPA+2.5%RHJ-3+1.5%KHm+1.5%water base Lubricant typeⅡ+barite,ρ=2.0g/cm³.Under the aging condition of 180℃,its plastic viscosity is 96m Pa·s,the dynamic shear value is 21.5m Pa·s and the filter loss is 17m L,which meets the basic performance requirements of construction.Through comprehensive performance evaluation experiments,the results prove that the drilling fluid has good rheology,temperature resistance up to 180℃,high temperature settlement stability,and has good anti-collapse inhibition.It has good effects on shale formations and micro-fracture pores in the Shunbei area.The developed stratum plays a role of anti-collapse and sealing.After anti-pollution evaluation experiments,the drilling fluid can resist NaCl pollution up to 30%,KCl pollution up to 25%,CaCl₂pollution up to 0.6%,and drill cuttings pollution up to 9%.It can be seen that its anti-pollution ability is strong.Meet the construction needs of Shunbei District.