Tóm tắt:

This study is the continuation of the work generated by Production and Drilling Research Project (PDRP) at New Mexico Institute of Mining and Technology with the purpose of developing a rheological model to quantitatively predict the thixotropic behavior. In order to do this, a number of shear relaxation tests were conducted at different fluid temperatures and bentonite concentrations. Five empirical correlations, which are the functions of fluid temperature and bentonite concentration, were attained based on the experimental data. These correlations are to calculate the five parameters existing in the PDRP’s model namely pre-exponential coefficient t  , inverse relaxation time 1/Tt, equilibrium yield point ye  , equilibrium consistency index Ke, and equilibrium flow behavior index me. With these five correlations, the rheological model to characterize the thixotropic behavior of a water based drilling fluid at any given bentonite concentration and fluid temperature is completely determined without the need of carrying other tests. The completed rheological model is then combined with the momentum equations to predict frictional pressure loss in pipe or annular flow. The results of this work make the prediction of thixotropic behaviors as well as the flowing bottom-hole pressure much simpler and quicker and hence help drillers’ response faster and more accurate during drilling operations.