Colorimetric Field Test For Determining Hydroxyethyl Cellulose (HEC) And Other Polysaccharides In Drilling Fluids
Authors: Malone Thomas R. , Raines Russell H. , Weintritt Donald J. 
Published: December 2007

Optimum use of high performance polymer-based drilling fluids has been hampered by the lack of a reliable field method for determining the polymer concentration once the circulating fluid composition is altered by drilled solids, new make up volume or by electrolyte-solids interactions. Standard physical methods, such as determining the fluid physical methods, such as determining the fluid viscosity and relating it to the polymer concentration, are of value only when new volume is being built in a mud tank, but become virtually useless in the course of a real drilling or completion operation. To overcome this limitation, a colorimetric field test has been developed based on the quantitative reaction of diphenylamine/glacial acetic acid reagents with filtrate from a polysaccharide containing drilling fluid. Industry users will benefit from the field test method by monitoring and maintaining optimum polymer content during drilling and completion, giving lover overall polymer cost per well. In the case of HEC, resultant advantages per well. In the case of HEC, resultant advantages include faster drilling rates in hard rock, longer bit life, gauge hole, less impairment of tight oil and gas formations and reduced formation damage on completion of the well. The field test can be run an either a portable spectrophotometer or by comparison with color standards.

Introduction

There is an accelerating trend in the formulation of drilling, completion and workover fluids to use high performance water-soluble or water dispersible polymers. These materials may be extremely polymers. These materials may be extremely efficient viscosifiers or they may be used primarily to reduce filter loss. In the main they tend to replace bentonite which remains the leading product for viscosity and filtration control. product for viscosity and filtration control. The impetus for the introduction of polymers in the oil field was not for the purpose of selling something competitive to bentonite. Rather their purpose has been to improve operations so that wells purpose has been to improve operations so that wells can be drilled in less time and completed with minimum formation damage. When small quantities of polymeric materials are used as additives to conventional muds, there is little danger that the concentration will critically affect the success of the drilling operation. On the other hand, where no bentonite is included in the initial makeup and where nearly all drilled solids are removed at the surface by solids control equipment, then knowledge of the concentration of polymer is vital for maintenance of hole stability and for optimum hydraulics and drilling rate.

It is accepted in the industry that the "all polymer" drilling fluids gain benefit by being polymer" drilling fluids gain benefit by being formulated with the proper concentration of inhibitive salts such as potassium chloride, sodium chloride or calcium chloride — indeed, a special field test to monitor the concentration of potassium chloride has recently been introduced. It potassium chloride has recently been introduced. It is no less important that the concentration of polymer be known if the mud engineer is to use polymer be known if the mud engineer is to use the best available drilling technology.

WHY A QUANTITATIVE POLYMER TEST?

In conventional drilling fluids there is an API standard test for bentonite content by methylene blue adsorption. This test has been extremely helpful in running almost all types of nondispersed and conventional muds. Indeed high weight drilling fluids in particular would be far more difficult to run without the aid of the methylene blue test. Similarly, the methylene blue test data is complementary to the polymer concentration test reported here and it is believed the two procedures will be companion tests run back to back. In fluid systems where polymers are the primary colloidal additive, it has become apparent that a method of measuring the amount of polymer in the circulating fluid is needed to sustain growth of this application in the face of the high unit cost of polymers compared to drilling mud grade bentonite.

The purpose of the paper therefore, is to describe a method for determining the concentration of polymer in the new drilling fluids. polymer in the new drilling fluids.