Rheological and yield stress measurements of non-Newtonian fluids using a Marsh Funnel Matthew T. Balhoff ⁎, Larry W. Lake, Paul M. Bommer, Rebecca E. Lewis, Mark J. Weber, Jennifer M. Calderin Petroleum and Geosystems Engineering, University of Texas at Austin, 1 University Station C0300 Austin, TX 78712–0228, USA abstract article info Article history: Received 30 September 2010 Accepted 10 April 2011 Available online xxxx Keywords: Marsh Funnel Yield stress Rheology Drilling mud Polymer Non-Newtonian Accurate and simple techniques for measurement of fluid rheological properties are important for field operations in the oil industry, but existing methods are relatively expensive and the results can be subjective. This is particularly true for measurements of fluid yield stress, which are notoriously difficult to obtain. Marsh Funnels are popular quality-control tools used in the field for drilling fluids and they offer a simple, practical alternative to viscosity measurement. In the normal measurements, a single point (drainage time) is used to determine an average viscosity; little additional information is extracted regarding the non-Newtonian behavior of the fluid. Here, a new model is developed and used to determine the rheological properties of drilling muds and other non-Newtonian fluids using data of fluid volume collected from a Marsh Funnel as a function of time. The funnel results for viscosity and shear-thinning index compare favorably to the values obtained from a commonly-used Fann 35 viscometer. More importantly, an objective, static method for determining yield stress is introduced, which has several advantages over dynamic, extrapolation techniques used for rheometer data. Published by Elsevier B.V. 1. Introduction 1.1. Non-Newtonian fluids in the petroleum industry Hydrocarbon production uses many fluids that are rheologically complex. Among these are cement, drilling muds, aqueous solutions of water-soluble polymer, and, of course, crude oil itself. Drilling fluids can be air or water, but most commonly they are “muds” or suspensions of solids in an aqueous or oleic fluid. The solids are suspended with one or more surfactants. The solids are to provide weight to the mud for pressure control, the main function of muds, but muds also lubricate the drill, carry drilling cuttings to the surface and cool the bit. Most muds are water-based as is the type used in this study. When fresh water is the liquid base, bentonite is the clay used for its superior properties necessary to achieve the goals stated for drilling mud. Salt water mud can be created using bentonite that has been pre-hydrated with fresh water so long as the salinity is not much more than that of sea water. Drilling mud exhibits several important rheological properties (Bourgoyne et al., 1991). The viscosity or consistency index of a mud is a measure of flow resistance. Therefore viscosity should be as small as possible to limit friction pressure. However a certain amount of viscosity is required to improve the solids carrying capacity of the mud. If viscosity is too small, the mud may be unable to suspend drilled solids at the desired pump rate. This requires the pumps to be run faster to continue to circulate drilled solids out of the well. If viscosity is too high, an excessive pump pressure will be required to circulate the mud at the desired rate. Higher than necessary pump pressure is an added strain on the pumps and piping and an added pressure in the bore hole that can lead to well bore stability problems. Water-soluble polymers are also used in drilling fluids to improve the ability of muds to lift cuttings, but they are also used as fracturing fluids to improve the removal of solids after fracturing, and in enhanced oil recovery. Two common polymers used are xanthan gum (hereafter just xanthan) and partially hydrolyzed polyacrylamide (HPAM). These are also used in the current study. These non-Newtonian fluids (drilling muds and polymers) may also exhibit a yield stress (or gel strength). For drilling operations, the higher the yield stress the more pump pressure will be required to initiate circulation. The yield stress can also be a desirable property because it will suspend the drilled solids and prevent or slow them from slipping back to the bottom of the hole during periods when there is no circulation. Fluid yield stress in fracturing fluids can help carry and suspend proppant, but can also make cleanup difficult (May et al., 1997; Balhoff and Miller, 2005). Journal of Petroleum Science and Engineering 77 (2011) 393–402 ⁎ Corresponding author. Tel.: + 1 512 471 3246; fax: + 1 512 471 9605. E-mail address: Balhoff@mail.utexas.edu (M.T. Balhoff). 0920-4105/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.petrol.2011.04.008 Contents lists available at ScienceDirect Journal of Petroleum Science and Engineering journal homepage: www.elsevier.com/locate/petrol