Barite Sag: Measurement, Modeling, and Management

Abstract

A joint industry project was established to study barite sag mechanisms and to develop field guidelines to manage the consequences. A simple empirical model was developed to compare sag potential for a wide range of fluid types. In the study, physical properties of the mud, wellbore conditions, and characteristics of the weighting material were shown to have a large influence on sag behavior. The study also included direct measurements of the properties of settled weight-material beds. These results provide new insight into the mechanisms of barite sag and how best to manage problems in the field.Data from the tests clearly demonstrate that the parameters affecting sag are interrelated and seldom act in isolation. For all muds tested, the highest sag occurred at low annular velocities over angles from 60 to 75°. Drillpipe rotation was particularly beneficial in minimizing barite settlement. Rotation also assisted in re-distributing barite deposits formed on the low side of the hole.The improved understanding of the mechanisms of barite sag enabled development of practical field guidelines. Case history studies presented in the paper demonstrate how the results of the work together with better field monitoring have been successfully applied to manage the effects of barite sag in high-pressure/hightemperature and extended-reach drilling operations.Test Fluids. The 20 test fluids represented a variety of mud types, formulations, weights, suppliers, and geographical sources. One of the project goals was to select muds from active directional wells ͑Ͼ30°͒ using weighted muds ͑Ͼ12 lbm/gal͒ in order to provide immediate feedback to operations. No other stipulations were made on field muds. Some laboratory-modified and laboratory-prepared fluids were also tested. Physical properties of all test fluids are listed in Tables 1 and 2. Mechanical-Parameter Results. Fig. 3 shows results for Mud 6 using the standard protocol at four inclinations ͑45, 60, 75, and 90°͒. Circulating fluid density change ͑corrected to 120°F͒ is plotted vs. time. All fluids tested responded similarly although the magnitudes varied.Most, if not all, of the sag-bed formation occurred at low flow rates and no rotation. Initial pipe rotation to 75 rpm consistently had the greatest effect on removing the beds. Doubling the rotary speed and then the annular velocity helped as expected, but to a much lesser extent.Time-segment 3 in Fig. 3, during which the sag was greatest, most clearly demonstrates the effects of angle. For Mud 6, the order of decreasing sag severity was 60, 45, 75, and 90°. While each individual mud tested exhibited slightly different behavior, the angle at which the maximum sag occurred was consistently in the range 60 to 75°. This is consistent with previously reported data. 3Fluid-Parameter Results. Rheology, density, weight material, and chemical treatments were the key fluid parameters investigated. These parameters emerged from an earlier study as the most significant variables affecting sag that can easily be controlled in the fie...

Development and Field Testing of a Unique High-Temperature/High-Pressure (HTHP) Oil-Based Drilling Fluid With Minimum Rheology and Maximum SAG Stability

“…In order to check the stability against settling of weight material, the oil-based MBS fluid was tested in a large scale flow loop following the test design described by Bern, et al 1 The oil-based MBS fluid was compared to a conventional HTHP oil-based fluid. In this test the influence of flow velocity and pipe rotation on dynamic barite sag is monitored.…”

“…It has been well documented in the literature that the potential for sag is considerably higher in oil-based drilling fluids when compared to their water-based counterparts. 1,2,3,4,5,6 The heightened tendency for sag in nonaqueous fluids is believed to be a function of the differences in structural build-up or the gelling mechanisms of the two systems. Consequently, employing conventional weight materials in the development of oil-based drilling fluids for HTHP drilling that possess acceptable rheology to minimize ECD while also maintaining satisfactory sag stability has been very difficult.…”

A Phenomenological Approach to Analysis of Barite Sag in Drilling Muds

“…They concluded that dynamic sag is partially related to low shear rate viscosity. The results of experimental studies by Bern et al (1996Bern et al ( , 1998) employed a dynamic sag flow loop. The apparatus contained an annulus with controllable eccentricity and the ability to induce relative rotation between the inner and outer walls.…”

Using Nanoparticles to Formulate Sag-Resistant Invert Emulsion Drilling Fluids

“…Barite sag in IEF is countered with a viscoelastic gel behavior (Sasson et al 1995;Sasson et al 1991) or increased low-shear rheology (Dye et al 1999;Kenny 1996). The low shear rheology is characterized by the low shear yield point (LSYP), typically a value from 7-15 lb/100ft 2 (Bern et al 1996;Bern et al 2000), is believed to impart sag resistance to the IEF. In the organoclay free IEF, low-gravity solids (clay-type materials and micronized calcium carbonate) are added to improve the rheology of the IEF.…”

“…This ability of the nanoparticles to provide stable water in oil emulsion has been used to formulate stable organoclay-free invert emulsion fluids free of low gravity solids like calcium carbonate and other clay-type materials. The nanoparticles used in the organoclay-free IEF provide good sag resistance without drastically increasing the fluid rheology, which usually delivers a viscous IEF with increased ECD (Bern et al 1996;Bern et al 2000).…”