Research On High-temperature(240℃ ) Water-base Drilling Fluid In Daqing Oilfield

For now, deeper and hotter reservoirs are considered in well drilling design with the continuous development of deep well drilling technology. High temperature stability of deep well drilling fluid is an important basis for the other performances of the drilling fluid. Due to high temperature, the changes of clay and treating chemicals take place,which lead to physical and chemical changes between the components of drilling fluid. It destructs properties of drilling fluid and impacts on the safty of drilling work. Consequently, it is necessary to conduct a new study on high-temperature drilling fluid.Based on the characters of deep reservoirs in Qingshen gas field, this paper studied on the Mechanisms of high-temperature drilling fluids.By optimized experiments, main treating chemicals and initial formula of new high-temperature drilling fluid were obtained.By experiments, focusing on HPHT rheological stability and filter loss performance, initial formula was perfected and adjusted.Finally, a new set of drilling fluid system which can resist high tempreture (240℃) was determined. Properties of new drilling fluid system before and after thermal aging were tested. The experimental results show that the new products can resist high temperature, alcium and salt, and they also have good rheological properties and the HTHP filter loss performance.It can not ignored that high temperature and pressure deeply affected the mud density.which made the mud density no long a constant.After new high-temperature drilling fluid were determined, the paper conducted a study on the effects of high temperature and pressure on mud density. Prediction Model of quiescent density, rheological parameter and equivalent circulating density of the new drilling fluid system.The models provided theoretic foundation of pressure management technology and have directive significance for downhole pressure control and complicated accident prevention.