Application Research Of High Temperature Resistant High Density Water-based Drilling Fluid System

There are 8 deep wells designed in the southern Junggar basin oil and gas reservoir, estimated at between 6100m-7700m, and the botton hole temperature can be reached 180? The geological conditions in the south of Junggar basin are very complex, so it is difficult to drill. In particular, the accurate information of the lower strata is not clear. The Dushan 1 design depth is 6185m, the information which lies 1280m below tugulu group is missing. The Dafeng 1 design depth is 7040m, the information which lies 2500m below the donggou group is missing. The unpredictability of different kinds of missing information of geology brings about great difficulty to drilling. Besides, taxihe formation condition is complex:illite smectite mixed layer, hydration capacity, and fracture development. The upper strata of the anjihaihe formation permeability is obvious, and the quite complex ground stress lead to well leakage. Ziniquanzi formation and Donggou formation result in well leakage, because there are multiple pressure systems in vertical plane, with a lot of complex formation.The southern Junggar basin formation is very complex, so this paper studies a set of high temperature and high density water based drilling fluid(named KGWTEK drilling fluid system). Firstly, the drilling fluid additive selection experiment is performed, including weighting agent, filtration reducing agent, surface active agent, diluent, lubricant and anti-high temperature plugging agent, which results in getting the drilling fluid additives of excellent performance. Secondly, non-weighted drilling fluid formulation is optimized with CPF, Redul-200, JNJS-220, KH-n, CPA, RH-220 and bentonite as variables by orthogonal experiment, then increases the density of drilling fluid to study the high density drilling fluid to optimize drilling fluid formulation, and evaluate the drilling fluid properties, including inhibition, anti-pollution, high temperature stability and sedimentation stability. Finally, the KGWTEK drilling fluid system is used in Dushan 1 and Dafeng 1.The formula of the KGWTEK drilling fluid system is consisited of 2.0-4.0%bentonite, 20%TX (tianze) alkali liquor,10%PPL,3.0%RSTF,5.0-10%CPF,0.5-1.0%Redul-200, 1.0-2.0%JNJS-220,5.0%TYJH-180,4.0-6.0%KH-n,3.0-5.0%CPA,2.0%CPI, 5.0-8.0%RH-220,1.0%OP-10,0.5%SP-80, barite,3.0%KCl,0.3%CaO and 1.0-3.0%solid lubricants. The drilling fluid properties are ranged as follows:density from 1.31g/cm3 to 2.60g/cm3,plastic viscosity from 27mPa-s to 56 mPa-s, FLAPI from 0.4 to 2.6mL,FLHTHP from 8.0 to 12 mL. In ordert to maintain the drilling fluid inhibition in the hydration layer, the KCl and the inhibitor CPI need to be added into; Increasing the Plugging agent KH-n in fractured formation is good for forming compact "shielding layer". Through the field test in Dushan 1 and Dafeng 1, The KGWTEK drilling fluid system accords with the drilling requirements of blind zone formation of basin in South Junggar, so it is a powerful guarantee for safety and fast drilling in the blind zone formation.