Affiliation:
1. Institut Français du Petrole
2. Solutia Europe SA
3. Royal Cosun
Abstract
Abstract
The oil industry is currently facing severe restrictions concerning the discharge of oilfield chemicals into the environment. For most of the actual widely used mineral scale inhibitors, the future will depend on the possibility of their re-injection into disposal wells. Another alternative could be the deployment of biodegradable chemicals. For this purpose a new class of "green" scale inhibitors, the Carboxy Methyl Inulins (CMI), has been evaluated in its ability to prevent carbonate and sulfate scale deposition by squeeze treatments.
Jar Tests and Tube Blocking Tests, performed on actual reconstructed injection and production waters show that the CMI inhibitors exhibit competitive inhibiting performances compared to currently used scale inhibitors. Core tests for the determination of CMI adsorption / desorption properties in static and dynamic conditions help to predict inhibitor squeeze lifetime and to design its implementation in future squeeze applications.
It is finally concluded that the Carboxy Methyl Inulins may already be considered as viable alternate mineral scale inhibitors to currently used but not biodegradable chemicals.
Introduction
The discharge into the environment of oil-field chemicals becomes more and more scrutinized and legislated. The oil offshore industry is particularly concerned by the severe restrictive regulations concerning the environmental impact of the products used. In the field of the mineral scale inhibition, chemicals are usually squeezed directly into the reservoir section surrounding the production well and back produced with the formation fluids. The only alternative for the produced water seems to lie between the re-injection on site or the use for the squeeze treatment of biodegradable chemicals.
Poly (amino-acids) and in particular polyaspartates have recently been evaluated1–3 as environmental safe "green" mineral scale and corrosion inhibitors. They have been also field tested4,5 in down-hole squeeze operations.
In the present paper a new class of biodegradable chemicals, the Carboxy Methyl Inulins (CMI)6, has been evaluated in its ability to prevent carbonate and sulfate scale deposition during topside or squeeze treatments. Their efficiency as scale inhibitors has been checked comparatively to that of the currently used phosphonates or polyacrylates by conducting Jar tests and Tube blocking tests. Their possible application in squeeze operations has been investigated by performing adsorption/desorption measurements on model limestones in static and dynamic conditions. In particular the influence of the composition of the production brine, used in the desorption step of the core-flood experiment, on the inhibitor return concentration was investigated. An experiment using Sea water as production brine was compared to an experiment using Forties water, which has a higher TDS and in particular a higher calcium content.
These tests seek to establish an evaluation of two different products but of very comparable structure. We tested the CMI and the polyacrylate. Both are polymers with carboxylic groups but with a very different structure of their polymeric chains.
Products.
Carboxy Methyl Inulins (CMI) are derivatives from Inulin. Inulin is a natural ß (2–1) polyfructoside with a glucose unit at the reducing end7. It is extracted from Chicory roots and used mainly in food applications. Carboxylate groups are introduced into the polysaccharide by carboxymethylation with Sodium monochloro acetate as reagent in alkaline medium (Figure 1).
Carboxymethyl Inulin is made at different degrees of substitution (DS:average amount of carboxymethyl groups / monosaccharide unit) and products are commercially available with a DS of 1.5, 2.0 and 2.5. The average degree of polymerization (DP) of the commercial product is DP=10.
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9 articles.
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