Research On Strong Plugging And Anti-Collapse Drilling Fluid Technology In Southern Sichuan Block

The oil and gas resources in Sichuan-Chongqing block are mainly natural gas,and the amount of oil and gas resources can reach more than 50%of the national natural gas reserves.However,the geological environment of shale gas in Sichuan-Chongqing block is complicated,and the instability of borehole wall sometimes occurs in the drilling process,and in the worst cases,the borehole wall collapse leads to technical difficulties in the drilling process of shale gas in China.In view of the above problems,the longmaxi Formation cuttings were sampled from a well site in southern Sichuan block,and the physical and chemical properties were analyzed.The results show that the clay mineral content of the rock samples in this block is up to 45.4%,including high illite and chlorite content,low expansion rate,and the formation is not prone to hydration.The development of fractures and micro-fractures is the main factor of stratum collapse,block falling and shaft wall instability.Aiming at problems of crack and the development of micro cracks formation,the introduction of particles with confidential filling theory,on the basis of screening the don’t match at the same level of superfine calcium carbonate particle rigidity,combined with the deformation of particles（oil soluble phenolic resin）,filling particles blocking agent（sodium microns）distribution,formed a set has a strong effect of broad-spectrum seal system:2%compound superfine calcium carbonate+2%oil-soluble phenolic resin+1%nano micron plugging agent,the plugging agent has good plugging effect,and the plugging rate of different sizes of micro-cracks can reach more than 90%.On the basis of using nano-sio2 particles as auxiliary emulsifier of water-in-oil emulsion,Pickering emulsion with stable emulsifying effect was prepared.By screening other oil-based drilling fluid treatment agents and combining with the use of broad-spectrum plugging system,a set of strong plugging and anti-collapse oil-based drilling fluid system formula was finally formed.The specific formula is as follows:240m L3#white oil+3%high temperature resistant main emulsifier XG-ZR1+2%hydrophobic nano-SiO₂+60ml30%Ca Cl₂brine+2%organic soil+2%MOTEX+4%calcium oxide+2%composite ultrafine calcium carbonate+2%oil-soluble phenolic resin+1%Boreplus+2%petroleum sulfonate+barite,The oil-water ratio is 80:20.The drilling fluid system has stable emulsifying properties and wide density range.It can completely plug nano-scale pores and fractures,and the plugging rate of 1-10μm micro-fractures can reach 99.2%.The plugging rate of 30～50μm micro-cracks can reach over 90%,resistant to 150℃high temperature,with good rheology,plugging,inhibition,settlement stability and resistance to cuttings invasion and other characteristics,to meet the needs of the site.