The previous General Agreement on Trade in Services (GATS) negotiations produced little liberalization of the movement of individual service providers (mode 4), and the potentially large global gains from such movement remain unrealized. In the current negotiations, as part of the Doha Development Agenda, developing countries are seeking greater openness in their area of comparative advantage: the movement of providers unrelated to commercial presence abroad. At the same time, many multinational firms would like easier intra-corporate movement of their personnel. We describe how this coincidence of interest could be harnessed to deliver greater openness at least for skilled service providers.

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A copublication of the World Bank and Oxford University Press.The findings, interpretations, and conclusions expressed here are those of the author(s) and do not necessarily reflect the views of the Board of Executive Directors of the World Bank or the governments they represent.The World Bank cannot guarantee the accuracy of the data included in this work. The boundaries, colors, denominations, and other information shown on any map in this work do not imply on the part of the World Bank any judgment of the legal status of any territory or the endorsement or acceptance of such boundaries. Rights and PermissionsThe material in this work is copyrighted. No part of this work may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or inclusion in any information storage and retrieval system, without the prior written permission of the World Bank. The World Bank encourages dissemination of its work and will normally grant permission promptly.

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Mineral scale build-up decreases permeability of the formation, reduces well productivity and shortens the lifetime of production equipment. Chemical scale inhibitors are commonly used in production wells to prevent scaling in the formation and/or in the production lines downhole and at the surface. An ideal scale inhibition treatment will last as long as possible and minimize the production interruption for treatment. In the art for introducing scale inhibitors into production wells, adding a solid scale inhibitor into the producing formation in conjunction with a hydraulic fracturing operation is often preferred to extend scale inhibition lifetime.This study quantified release rates of a solid scale inhibitor for use in fracturing treatment. Tests were conducted under dynamic conditions with various loading rates as a percentage of sand proppant. Results show that this solid derivative of a phosphonate inhibitor has a sustained long-term release profile. Inhibitor release rate gradually increases with solid inhibitor loading. However, this effect slows when the loading exceeds 5% (wt/wt).Based on the test results, a mathematical model was developed to describe the release rate profile and thereby predict the long-term behavior of inhibitor returns from initial solid inhibitor loading. Actual data collected from treated wells were compared to the mathematical model. The earliest wells treated with this type of product have achieved 5 years of production with continued effective residual chemical measured in the produced water. Other wells treated have achieved greater than 1 million barrels of produced water with continued effective residual chemical measured in the produced fluid. The data from this laboratory release study have verified that additional long-term protection can be achieved by increasing initial loading rates. IntroductionTraditionally, liquid chemical inhibitors were primarily used to control the formation of scale in oil and gas production. These chemicals can be administered through batch, continuous or squeezed applications (Szymczak et al., 2006). A main drawback of conventional squeeze treatments in a carbonate formation is that most of the acidic phosphonate inhibitor is precipitated near the formation face because the reaction of acid with carbonate and the formation of Ca-phosphonate precipitation take place very quickly. As a result, only limited reservoir protection distance can be provided near the wellbore. In a sandstone formation, the squeeze treatment depends on adsorption of the phosphonate inhibitor on the formation. Adsorption squeezes are often performed in reservoirs where a neutralized inhibitor pill solution is injected into the formation. However, compared with precipitation squeeze, little or negligible amount of inhibitor can be retained and released slowly from the formation. A large fraction of the phosphonate tends to flow back within a few days and then decreases to an extremely low value, which is not enough to effectively inhibit scale formation (Shen, et al., 200...