An Analytical Method for Emulsifier Concentration in an Oil-Base Drilling Fluid
Authors: Matherly R. 
Published: December 2007

Summary
A laboratory procedure has been developed to determine the emulsifier content in an invert emulsion drilling fluid using chromatographic techniques. A detailed description of the new procedure is presented, along with some field case histories and the results of a study on the effects of high temperatures on emulsifier content. This new procedure has direct field applications both to improve the performance and lower the cost of invert emulsion drilling fluids.

Introduction
Invert emulsion, or oil-base, drilling fluids are used in drilling troublesome shale formations, water-sensitive production zones, and highly pressured hot formations. Recently, they have been used for penetration rate advantage as well.Invert emulsion fluids contain special surfactants that permit the formation of the water-in-oil emulsion and maintain its stability. These are called simply "emulsifiers" in this paper. The internal water phase of the emulsion typically is a sodium chloride or calcium chloride brine.Only a small quantity of emulsifier is required for an invert emulsion. Overtreatment with emulsifiers is costly. Undertreatment is even more costly if it results in failure of the emulsion and consequent water-wetting and settling of barite and drilled solids.Heretofore, there has been no procedure for determining the emulsifier content in invert emulsion drilling fluids. Interferences by the oil itself precluded determination.Now, however, a laboratory procedure has been developed to determine the emulsifier content in a drilling fluid. This new procedure has direct applications both to improving the performance and lowering the maintenance costs of the invert emulsion drilling fluid. Another application is the study of the chemical behavior of invert emulsion drilling fluids under various conditions. it is not known how much emulsifier is lost by coating out on shale and being discarded over the shaker screens. This loss also can be determined using the procedure. Finally, the test procedure is applicable to most manufacturers' invert emulsion drilling fluids since it is based on chemistry common to all invert emulsion drilling fluids.

Theory
Most invert emulsion drilling fluid concentrates contain fatty acids as the major emulsifier. Without any hydrocarbon contamination, they can be chromatographed to determine purity. However, in a drilling fluid, the diesel content interferes with the analysis in such a way as to cover up completely the chromatographic peaks from the fatty acids. The key to the new procedure is to react the fatty acids used as an emulsifier with a compound to produce a chlorinated fatty acid. This chlorinated derivative can be distinguished easily from the diesel by the use of a chromatographic detector that is highly sensitive to chlorinated compounds, such as an electron capture detector.The use of derivatives in chromatography is common. They are used either to improve the sensitivity of the chromatograph to a compound or to distinguish a compound from its matrix. The use of chromatographic derivatives in the drilling fluids industry, however, has been very limited. The basis for the derivative used in this procedure is from work done in the past to lower the detection limit of aromatic carboxylic acids.
JPT
P. 1389^