Study Explores Effect of Solids on Topside Operations in an EOR Context

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 216848, “Impact of Solids on Topside Operations in EOR Context,” by Christian Blázquez, Marie-Hélène Klopffer, SPE, and Eric Kohler, IFP Energies nouvelles. The paper has not been peer reviewed. The presence of solids in hydrocarbon treatment and separation equipment downstream of the choke can have a significant effect on process operability, assets risks, and flow assurance, therefore affecting operational economics. In the complete paper, the effect of solid particles on oil/water (O/W) separators (i.e., emulsion stability) and on produced-water treatment has been studied. In this study, six different solids were chosen, three representing reservoir solids (sand, illite, and kaolinite) and three for scale and corrosion solids [calcium carbonate (CaCO3), barium sulfate (BaSO4), and iron sulfide (FeS)]. All solids used were characterized in terms of composition and size; for modified solids, their wettability also was measured. The sand sample was fully water-wet, while the wettability of the CaCO3 and the BaSO4 could not be measured. For the rest of the particles, contact angles lower than 90° showed water-wet properties. A crude oil from offshore Brazil was used. The oil is a heavy one that is quite viscous at normal conditions. The oil also is acidic with high content in polar components. The polymer used is xanthan gum. The ability of the solid particles to stabilize O/W emulsions depends on several factors, such as particle concentration, size, shape, and wettability. During this work, the evaluation of the effect of the selected particles on the stabilization of a 50% water-cut emulsion was performed in two steps. Before studying the effect of different solids on O/W separation in the presence of xanthan, the effect of solid concentration and nature was investigated through rapid emulsion tests. Afterward, the most-troublesome particle concentrations were evaluated in the presence of polymer and demulsifier. Effect of Solids Without Polymer. The rapid emulsion test was developed based on Tessari’s test method for the formation of medical foams. The basic principle is to produce an emulsion by forcing the oily and the aqueous phases to repeatedly experience a restriction. The resulting emulsion is poured into a glass tube. The experimental temperature is 50°C, and the water cut is 50%. O/W separation kinetics are followed for 60 minutes. In addition, the oil-in-water at the end of the test is evaluated by visual comparison with the reference case (no chemical analysis is performed during this phase). The effect of the solid particles on O/W separation depends not only on their nature but also on their concentration. Reservoir Solids. The presence of sand did not affect separation performance, presumably because of the large granulometry and reduced surface area. The sand settled quickly to the bottom of the flask, entraining some of the oil and thus affecting water quality. On the other hand, both clays affected the separation kinetics. When illite was used, no matter the concentration, the amount of settled water was lowered. Similar results were found when kaolinite was used. When the clays were modified, however, separation kinetics were clearly affected. In the case of illite, separation kinetics were improved with respect to the unmodified solid, while, in the case of kaolinite, the emulsion was further stabilized, producing a tighter emulsion.