BAKER HUGHES - Drilling Fluids Reference Manual

Baker Hughes Drilling Fluids
MBT (Methylene Blue Titration)
Methylene Blue Testing provides field measurement of the reactive clay content of a drilling fluid.
The PERFFLOW ® DIF system is formulated with no reactive clays. Minimal clay content in the
system is desired so as not to promote any damage to the reservoir.
PH (API 13B-1) Field measurement of drilling fluid (or filtrate) pH and adjustments to the pH are
fundamental to drilling fluid control. Clay interactions, solubility of various components and
contaminants, and effectiveness of additives are all dependent on pH, as are the processes that control
acid and sulfide corrosion.
Note:
See Donvan, J. P. and Jones, T. A.,“Specific Selection Criteria and Testing Protocol
Optimize Reservoir Drill-In Fluid Design”, SPE 30104, May 1995 for a more detailed
discussion of drill-in fluid selection and testing
Filter Cake Formation and Dispersability
Fluid loss or leak-off is effectively controlled by bridging the pore openings with rigid or semi-rigid
particles of sufficient size and number. However, in order to ensure that the filter cake can be
effectively removed after placing the well in production, it must meet two important requirements:
The fluid must possess the right particle size distribution and particle concentration to build a filter
cake that will quickly and effectively bridge the pore openings.
The fluid must deposit a filter cake that is highly dispersive to the produced fluid. A quick and
effective particle bridge will limit particle invasion to maximize return permeability. In addition, a
highly dispersive cake will be removed by the production fluids, thus requiring no acidizing or
treatment with breakers.
The scanning electron microscope is a very useful tool to guide the selection of the bridging materials
since one can obtain a microscopic picture of the filter cake in place. Figure 1-15 shows a
photomicrograph of a PERFFLOW ® filter cake on a 3-Darcy filter media. These are lateral or crosssectional
views of the cake deposited on the filter surface. Note the clean delineation between the
filter cake on the left and the surface of the permeable rock. Intrusion of calcium carbonate bridging
particles has been limited to the first few micrometers of the rock surface.
Baker Hughes Drilling Fluids
Reference Manual
Revised 2006 1-39