Synergy between chemical demulsification and electrocoalescence: From bench to large scale
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Production of crude oil from reservoirs always contain additional fluids, namely formation water and gas that occur naturally below the surface or seabed. Especially problematic is the water that becomes dispersed within the oil phase, known as water-in-oil emulsions, through high-pressure changes across chokes and valves during pipeline transport from the reservoir to the platform. There are both economical and regulatory incentives for separating these reservoir fluids. Water-in-crude oil emulsions have been recognized as a long-standing transportation and processing issue within the industry. There are several available options for resolving this problem, like chemical demulsification and electrocoalescence. Each method, when used individually, has proven to yield efficient oil/water phase separation. However, limited research has been conducted on their combined effects. The aim of this thesis was, therefore, to uncover any existing synergy between the use of both chemicals and electric field for water resolution from crude oil emulsions. Additionally, the goal was also to identify mechanisms of demulsification for the chemicals used, as well as to understand the interplay between the electric field and chemical demulsifiers to improve droplet coalescence in crude oil emulsions. The work of the thesis was divided into four papers, where methods of increasing scale have been applied. The gradually increasing scales were used to develop a better understanding of how small-scale mechanistic interactions affect larger-scale interactions. In the first paper, the idea was to first develop an understanding of the mechanisms of crude oil components, chemicals and electric fields for attraction and coalescence between a pair of droplets in model oil. In the second paper, laboratory bench-scale crude oil emulsions were emulated as they appear in industrial conditions at high temperature. The focus of this paper was to develop a next-generation low field NMR method for quantifying oil-water separation by chemical demulsification (without electric fields). This NMR method was then used to acquire continuous real-time visualization of the sedimentation of water droplets and the development of the droplet size distributions. This information was used to attempt to probe the mechanisms of four different demulsifiers at play during emulsion separation. In the third paper, the same NMR method was applied to study emulsion separation at bench-scale by both chemical demulsification and electrocoalescence to determine any existing synergy. Two chemical demulsifiers were selected from the study in the second paper based on promising performances. These were then studied in combination with electric AC fields for crude oil emulsion separation. The synergy emerged most clearly at low to moderate chemical concentrations and low AC fields, where either factor would not dominate the separation. Above certain fields, chemical effects were marginal and electrical effects became dominant in separation. The goal of the last paper was to compare the separation efficiency of crude oil emulsions by chemicals and electric field, assessed by different methods of analysis. Techniques were tied to different scales, from 2 ml to 100 ml emulsions. A comparison was also drawn between the use of AC and DC electric fields in terms of separation efficiency. Several factors, such as chemical concentration and composition, electric field type, temperature, and strength were studied.