Equipment and Methods of Measuring High Temperature Rheology of Drilling Fluids

Since the six-speed direct reading viscometer is unable to measure the change of mud rheology with downhole temperature, downhole pressure, downhole shear rate and time, drilling fluid researchers turn to the high temperature high pressure (HTHP) rheometer for evaluating the rheology and thermal stability of drilling fluids, hoping that it will give more scientific and effective test results. To simulate the actual mud properties downhole, several test methods are established, which are test of low shear rate viscosity, test of loss of viscosity at high temperatures and test of changes of mud viscosity with time at dynamic and static conditions. These tests are used to characterize the cuttings carrying capacity, rheology at elevated temperatures and high temperature stability of drilling fluids at dynamic and static conditions, the test results can reveal the actual rheology of the drilling fluids downhole. Field application of the HTHP rheometer in testing the properties of the organic salt drilling fluid used in drilling the well Chengtan-1 indicated that the test method can be used to provide field engineers with accurate data for judging whether the mud properties can meet the requirements of drilling operation under high bottomhole temperatures. The test method and the HTHP rheometer have provided a scientific and reliable way of designing, developing and using high temperature drilling fluids and mud additives, and greatly made up for the shortcomings and defects of using the six-speed viscometer to measure the rheology of drilling fluids.