Rheology of Various Drilling Fluid Systems Under Deepwater Drilling Conditions and the Importance of Accurate Predictions of Downhole Fluid Hydraulics

Abstract

Previous rheological studies of water-base and oil-base muds have concentrated on fluid viscosities at elevated temperatures and pressures. This paper extends the data available to cold temperature regimes which can be expected to occur in the riser for deepwater wells. The rheology of eighteen different drilling fluids covering WBM, OBM and SBM have been evaluated between -1° to 90°C and 1 to 344.7 bar. The Herschel-Bulkley and Casson models both fitted the OBM and SBM rheograms very well. For the different WBM systems, the Herschel-Bulkley model also fitted the salt/polymer fluids and unweighted bentonite-based fluid rheologies, however, the Casson model best described the weighted bentonite-based fluid rheologies. The effect of the cold fluid viscosity in the riser on ECD for deepwater wells was assessed using a software model which uses a transient temperature simulator in conjunction with a hydraulic model which accounts for different mud viscosity throughout the wellbore. Comparing the ECD predictions with those calculated where the mud rheology is independent of temperature and pressure, the ECD was found to be underestimated by up to 6.1% for a SBM and overestimated by 3.1% for a WBM. If there are formations with small differences in the fracture and pore pressure gradients, then these variations in ECD could cause well control problems.

Rheological properties of oil-based drilling fluids at high temperature and high pressure

“…A possible procedure for implementing the model is: Firstly, according to our model experiments should be made at HPHT in order to determine the characterized constants for the specific drilling fluid in use, which are required for accurate extrapolation of rheological parameters to downhole conditions. Secondly, to accurately predict the rheological parameters throughout the wellbore requires an accurate transient temperature and pressure profile to be calculated [7] . It can be obtained using a transient temperature and pressure simulator, and it has been described in detail elsewhere [8] .…”

Silica Nanoparticles for the Stabilization of W/O Emulsions at HTHP Conditions for Unconventional Reserves Drilling Operations

“…However, at high temperature and high pressure, drilling fluids are likely to exhibit thermal degradation and breakdown of surfactants/ emulsifiers leading to drastic inconveniences such as sagging, syneresis and formation damage, etc. (Davison et al, 1999;Garcia and Parigot, 1968).…”

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

“…Several investigations have been conducted to determine the effect of pressure and temperature on density of a variety of drilling fluids, and empirical correlations have been proposed (Hoberock et al (1982), Isambourg et al (1996), Hemphill and Isambourg (2005), Demirdal and Cunha (2006)). Several authors investigated changes in rheology of drilling fluid under downhole conditions and its effect on accurate predictions of downhole fluid hydraulics (Davison et al (1999), Demirdal and Cunha (2006)). …”