A Method of Predicting High Temperature High Pressure Rheological Property Based on Viscometer Readings

Prediction and analysis of high temperature high pressure (HTHP) mud rheological property together form the basis on which drilling fluid property control and hydraulic parameter calculation for deep and ultra-deep wells are performed. This paper introduces a method of analyzing HTHP drilling fluid rheological property using viscometer readings. In developing the new method, the pattern of the rotational viscometer readings changing with temperature and pressure is analyzed using data from laboratory HTHP experiments. The readings at different rotational speeds are then normalized using factors of proportionality. Using numerical method, the relationship among the factor of proportionality, temperature and pressure at constant pressure changing temperature and constant temperature changing pressure is analyzed. A model for predicting HTHP factor of proportionality and a general model for predicting HTHP viscometer readings are established based on the analyses. Methods of selecting HTHP rheological model and calculating rheological parameters are also developed. The calculated rheological parameters and the measured ones fit very well, as shown by comparing two sets of parameters. Using the method, a set of rheological data of a drilling fluid taken from a wellbore is analyzed. Compared with conventional methods, this new method can be use to predict not only normal rheological properties (plastic viscosity, apparent viscosity etc.), but also HTHP parameters of all rheological models.