| The effective regulation and control on the rheology and filtration loss under high-temperature and high-pressure is one of the major technical problems for water-based drilling fluids with high-density in deep wells, the key of which is to increase the colloidal stability of drilling fluids under high-temperature. And to fully understand the mechanism of high-temperature resistance of drilling fluid is the key technology in designing and producing the high-temperature resistant water-based drilling fluids. Based on the designed high-temperature high-pressure (HTHP) multi-function experimental apparatus LH-1 for dynamic evaluation, three kinds of high-temperature resistant additives, which are high temperature colloid protecting agent GHJ-1, high-temperature fluid loss additive GJZA-1 and high-temperature calcium/salt resisting mud thinner JNL-1, and two high-temperature resistant salt/fresh water-based drilling fluid systems with high density were developed in this paper. Focusing on the two systems, researches on the mechanism of high temperature resistance, fluid overall performance and fluid rheology under HTHP are carried out.With the designed HTHP multi-function experimental apparatus LH-1 for dynamic evaluation, the fluid properties can be evaluated under 300℃in temperature and 40MPa in pressure, such as dynamic and static HTHP filtration, plugging, aging and dynamic drilling cuttings scattering and sealing of drilling breaks. It is proved that this instrument is of high accuracy and reliability, with intelligent operation and data processing. GHJ-1, high-temperature colloid protecting agent, improves the overall performance of the drilling fluid systems for its good compatibility with sulphonate additives commonly used in deep wells, its high salt/calcium resistance and effective colloid protection under high temperature (240℃). GJZA-1, fluid loss agent, reduces the viscosity of the system effectively. JNL-1, polymer viscosity reducer, has good capability in adjusting the rheology of the system with high-density under HTHP for its high temperature and salt/calcium resistance. The produced salt water-based drilling system, with density as 2.2g/cm3 and temperature resistance as 220℃, and fresh water-based drilling system, with density as 2.2g/cm3 and temperature resistance as 240℃can effectively protect the oil/gas formation because of the good-inhibition, high anti-pollution capability and adjustable rheology and filtration loss. Furthermore, the anolysis on the rheology data showed that H-B model was the best in depicting fluid rheology under high-temperature. A mathematical model was built to simulate the relationship between the apparent viscosity and temperature/pressure.
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