Synthesis of Sulfurized Fatty Acid Ester and its Application in High TemperatureHigh Pressure Drill-in Fluids

In high temperature extended reach well drilling, the water-based drilling fluids are generally treated with liquid lubricants to alleviate friction. In high density, high salinity and high temperature conditions, the lubricity of the liquid lubricants is not enough to reduce the friction to the required level, causing from time to time downhole troubles such as halting of drilling string, stuck pipe and wear and tear of drill tools. To solve these problems, a sulfurized fatty acid ester is synthesized in laboratory and is compounded with lubricants to obtain a compound lubricant QT311. Adding the lubricant QT311 into the HTFlow high temperature high pressure water-based drilling fluid greatly improves the lubricity of the drilling fluid. Testing the QT311 treated HTFlow drilling fluid on four-ball friction tester shows that treatment of 1%QT311 reduces the coefficient of friction by 64% and the diameter of the wear scars is reduced by 43%. These results indicate the QT311 as a lubricant is superior to several widely used commercial lubricants. Analysis of the surface of the friction pair with SEM shows that QT311 react chemically with iron during friction to form sulfur-iron extreme pressure membrane, thereby improving the friction-reducing performance of the drilling fluid. The laboratory experiments also show that QT311 has excellent compatibility with the HTFlow drilling fluid, anti-hydrolysis performance, salt resistance and high temperature resistance. The experimental results have provided a reference for further studies on drill-in fluid lubricants.