Study On High Temperature And High Pressure Constant Rheological Water-based Drilling Fluid System In Deep Water

In the process of deep-water drilling,the viscosity stability of drilling fluid at low temperature is the key to ensure the safety,economy and success of drilling.At present,the existing drilling technology is difficult to solve the problem of deep-water temperature sensitivity of drilling fluid.The existing water-based drilling fluid adopts polymer viscosities,and the polymer and the molecular chain will curl,twist or stretch when the temperature changes,affecting its viscosity control effect.The water-based drilling fluid has a strong correlation with temperature,and the temperature drops and the viscosity rises sharply.And although widely using oil-base drilling fluid to work abroad,but for offshore drilling operation,using oil-base drilling fluid to work due to the environmental protection and economic cost,is not the best choice at present,and therefore need to analyze the existing water-based drilling fluid improvement and optimization,in order to reduce the temperature influence of water-based drilling fluid.In this paper,the deep high temperature and high pressure gas well is easy to form gas hydrate,the rheological properties of low temperature drilling fluid instability,high temperature and pressure to drilling fluid rheology and fluid loss is difficult to control,the problem such as safe drilling fluid density window is narrow,puts forward a set of suitable for the constant flow of deep high temperature and high pressure formation drilling fluid system,the system basic formula is:2%Seawater bentonite slurry+0.6% NaOH+0.3%G-61+0.1%BIOVIS+4%SPNH-HT+2%FT-1+2%POLY-D+STBHT+20%Na Cl+10%HCOOK+2%HLX-L+BARITE.??=1.5g/cm³?Experimental results showed that the deep high temperature and high pressure constant flow water base drilling fluid system has good viscosity-temperature properties,change between 4? to 70?,and the system viscosity change smaller,especially YP and ?₆/?₃ can keep constant with the rheological characteristics of constant under various temperature,and API fluid loss is low,only 2.7 ml,HTHP under 150?water loss is only 15.0 ml,system ability to resist temperature of 220?.The simple formula of the system is easy to adjust,which can adapt to the needs of deep water high temperature and high pressure formation drilling.The system has good weighting performance,and the rheological property of the system is relatively stable at all densities,especially the constant rheological characteristics are obvious.Moreover,it has a high anti-fouling performance.Under the invasion of a small amount of calcium salt,a large amount of sand,cuttings and seawater,the performance of the system changes little,especially the constant rheological characteristics can be maintained within a stable range.The high temperature and high pressure constant rheological water-based drilling fluid system in deep water has high inhibitive and lubricating performance,and the inhibition performance of the system is more than 85%,which can meet the requirements of drilling operation,and the friction coefficient is also low.The inhibition of hydrate in low temperature and high pressure layer is also good:the drilling fluid pressure is 20MPa and the temperature is 3?,and the pressure is still19.9mpa after 23 hours,indicating that this system can effectively inhibit the formation of hydrate.