Novel Polymer Modifications Lead to Next-Generation Pour-Point Depressants

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 187386, “Next-Generation Pour-Point Depressants Based on Novel Polymer Modifications,” by Sabine Scherf and Albert Boddien, Sasol Germany, prepared for the 2017 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, USA, 9–11 October. The paper has not been peer reviewed. Current logistics and pipeline-infrastructure limitations make transportation and production of waxy crude oil challenging, necessitating a step change in the chemistry required to mitigate crude-oil-composition issues. For wax prevention, pour-point depressants (PPDs) or wax inhibitors usually are used. A new approach makes use of a special hydrophobe modification in typical polymer systems that significantly broadens the systems’ applicability. Introduction Several wax-control strategies are available in the oil industry. Waxy crude oils are sometimes mixed with a diluent to avoid deposits. The diluent can be a gas condensate, natural-gas liquid, or a lighter crude with a lower wax-appearance temperature. Other possibilities include heating pipelines and isolations, mechanical removal by pigging and wireline cutters, ultrasonic techniques or magnets, microbial treatments or wax dissolvers, wax inhibitors, PPDs, and dispersions. Many polymer compounds are described as PPDs; the ones most extensively used for crude oils are ethylene-vinyl-acetate (EVA) copolymers, poly-n-alkyl acrylates, methacrylate copolymers, and styrene-maleic anhydride copolymer esters. PPD polymer systems incorporate into the wax crystal and alter or even disrupt the crystal structures. Polystyrene-maleic anhydride (PSMA) copolymers can be modified easily with alcohols, amines, or other materials, which render them suitable to adjust the PPD performance for crude oil. However, until recently, research has focused on the effect of the polymer additives on the crystal structure of treated waxes in the crude oil and not on the applicability of the PPD itself. The PSMA PPD polymer systems are solids and must be solubilized by suitable solvents in order to be applied under field conditions. Equipment and Processes Synthesis. The polymeric backbone of styrene-maleic anhydride was synthesized by radical polymerization of styrene and maleic anhydride. In a second step, the respective copolymer was esterified with a fatty alcohol or mixtures thereof. The final product contained approximately 40% alcohol copolymer ester in xylene. The copolymer ester is characterized by complete saturation (92%) of the carboxylic groups with heavy alcohol molecules. The general structure of such a PSMA copolymer esterified with different alcohol mixtures is outlined in Fig. 1. Model Oils. Two model oils were prepared to mimic waxy crude oils with high paraffinic content and different carbon number distributions of the n-alkanes. The model oils were prepared by mixing 14 wt% synthetic paraffin waxes in n-decane. Alcohols. The styrene-maleic anhydride copolymer was reacted with behenyl al-cohol, C24+ alcohol, and mixtures of behenyl alcohol or C24+ alcohol with 2- tetradecyl octadecanol. Equipment and Methods The pour point (no-flow point) is the lowest temperature at which a crude oil stays fluid when it has been cooled under static conditions. The determination of the pour point was made by use of ASTM D5985, Standard Test Method for Pour Point of Petroleum Products (Rotational Method).