The Effect of Temperature and Pressure on the Viscosity of Oil-Base Muds

Abstract

Introduction The viscosity of oil-base muds can be determined over a wide range of temperature and pressure using the BHC Viscometer. This instrument consists of two concentric cylinders mounted in a 20,000-psig autoclave that has an upper operating-temperature limit of 650 degrees F. The inner cylinder, or rotor, is connected by a magnetic couple to a Haake Rotovisko. A detailed description of the instrument has been published previously. In operating the BHC Viscometer, the autoclave is completely filled with mud and sealed. The rotor is rotated at a constant rate and the sample is allowed to reach an equilibrium temperature. The pressure is then adjusted with an auxiliary pump and the shear stress is recorded for each shear rate. The instrument was calibrated by first calculating the shear rates from the viscometer dimensions. This method gave shear rates of 11, 21, 32, 64, 96, 191, 286, 573, and 860 sec-1. The mean shear-stress constant was then determined experimentally to be 8.1 dynes/cm2/scale part (1.6 lb/100 ft2/scale part). Discussion The best mathematical description of the viscosity of an oil-base mud at constant temperature and pressure is the power-law model. The linear form of this model is power-law model. The linear form of this model is(1)ln = ln K + n ln y However, two sets of constants are required, one set for use at shear rates below ~ 200 sec and the other set for the higher shear rates. The analysis of the pressure and temperature effects shows that the logarithm of the shear stress is directly proportional to the pressure and inversely proportional to proportional to the pressure and inversely proportional to the temperature. These relationships can be expressed by the following equations:(2)ln p, JPT P. 884

Importance of Drilling Fluids' Rheological and Volumetric Characterization to Plan and Optimize Managed Pressure Drilling Operations

“…Since the rate of change in yield stress is minimal at high temperatures, the relation between yield stress and temperature is also expressed using a power function as follows: 4.5 θ600-θ3* θ600-θ3 θ600-θ3 θ600-θ3 θ600-θ3 27.0 θ600-θ3 θ600-θ3 θ600-θ3 θ600-θ3 θ600-θ3 49.0 θ600-θ3 θ600-θ3 θ600-θ3 θ600-θ3 θ600-θ3 93. 5 θ600-θ3 θ600-θ3 θ600-θ3 θ600-θ3 θ600-θ3 138.0 θ600-θ3 θ600-θ3 θ600-θ3 θ600-θ3 θ600-θ3 * Shear rates: 600 rpm, 300 rpm, 200 rpm, 100 rpm, 6 rpm, 3 rpm Similar to plastic viscosity, coefficients δ and φ are dependent on operating pressure conditions. A closer look at Figure 2 shows that the fluid under investigation has a higher yield point at 101 kPa compared to yield point values at other operating pressures.…”

“…For this reason, it is important to determine the response of the rheological parameters to wellbore conditions in order to fully understand the fluid performance and estimate parasitic pressure losses along the wellbore. Several investigators have attempted to model the effect of temperature and pressure on drilling fluid rheology through the shear rate history of the fluid (4)(5)(6)(7)(8)(9)(10)(11)(12) .…”

Determination of drilling fluid rheology under downhole conditions by using real-time distributed pressure data

“…Over the past years, several studies were performed to find correlations between the rheological parameters of the drilling fluids and the effects of temperature and pressure. For instance, Annis (1967), Hiller (1963) and Alderman et al (1988) studied the rheology of water-based mud under HPHT conditions, while the rheology of invert drilling fluids (OBM/SBM) under HPHT conditions was investigated by McMordie et al (1975), Bailey et al (1986), Politte (1985), Houwen and Geehan (1986).…”

Interaction of Water With Organophilic Clay in Base Oils To Build Viscosity

“…6,7 In their model, individual water molecules form hydrogen bonds (through the oil phase) with the edges of organophilic clay platelets.…”