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Oilfield Chemistry

Sulfide scales are becoming more prevalent in the oilfield environment. There are several reasons for this, including higher-pressure and -temperature fields being developed, which can be associated with the formation of zinc and lead sulfide; fields maturing, with iron sulfide being often associated with old mature waterflooded fields; and sour production becoming more commonplace, resulting in more-challenging integrity management.

Little comprehensive research has been conducted on sulfide scales when compared to that concerning conventional carbonate- and sulfate-scale species. Perhaps this is partly because of the challenge of studying these materials in the laboratory and the perception that iron sulfide formation in the oil field is protective of tubulars and production equipment.

As the prevalence of these scales increases, so too does the focus being placed on them by the industry, academia, and independent research groups. However, a lot of space remains for innovation and understanding.

Today, the correct mitigation and cleanup methods can be selected most appropriately only on the basis of accurate root-cause-of-failure analysis. Generally, no single solution can be applied to all systems because the root causes differ from system to system. Commonality exists, however, insofar as a combination of dissolver/chelant and surfactant is nearly always needed for cleanup of the typically oil-wet scale.

Control methods have focused very much on indirect techniques of removing one of the scaling species, such as chelation and sequestration of either the metal cation or the sulfide in order to reduce supersaturation. However, as the formation environments become more severe, these methods are being found to be increasingly challenging as they typically involve stoichiometric amounts of preventive chemicals. More recently, however, threshold inhibitors are starting to be reported in the literature, including some very promising chemistry evaluations from several research groups. Critical to success here is the accurate testing in the laboratory that best approximates field conditions. Unlike with conventional scale types, this is very easy to get wrong, so great care must be taken when intending to realize conformity between laboratory testing and success in the field. One thing is certain: More work needs to be performed by the industry before it can be said that control of these scales is understood and is as easy to manage as it is for conventional scale species.

This Month's Technical Papers

Sulfide-Scale-Formation and -Inhibition Tests for a Gas-Condensate Field

FeS-Scale Cleanout With High-Pressure Coiled Tubing and Tailored Fluid

Kinetics and Inhibition of Ferrous Sulfide Nucleation and Precipitation

Sulfide/Calcium Carbonate Scale Coprecipitation

Recommended Additional Reading

SPE 169777 Sulfide-Scale Control: A High-Efficacy Breakthrough Using an Innovative Class of Polymeric Inhibitors by A.J. Savin, Clariant Oil Services, et al.

SPE 169808 An Advanced Method for Preparing Ferrous Sulfide and Testing Potential Inhibitors by Robert G. Fowles, Weatherford, et al.

SPE 169810 Mechanisms, New Test Methodology, and Environmentally Acceptable Inhibitors for Codeposition of Zinc Sulfide and Calcium Carbonate Scales for High-Temperature Application by Christopher Tortolano, Nalco Champion, et al.

SPE 168196 A Comprehensive Geochemical-Based Approach To Quantify Scale Problems by Aboulghasem Kazemi Nia Korrani, The University of Texas at Austin, et al.

Jonathan Wylde, SPE, is the head of global innovation at Clariant Oil Services in Houston. He is responsible for research-and-development activities, including innovation, method development, and technical support. Wylde holds a BS degree in geology and a PhD degree in physical chemistry from the University of Bristol. He is author or coauthor of 75 papers and holds multiple patents. Wylde serves on the JPT Editorial Committee and on committees for the SPE International Conference and Exhibition on Oilfield Scale and the SPE International Symposium on Oilfield Chemistry. He also serves as a technical editor for SPE Production & Operations and SPE Journal.

Oilfield Chemistry

Jonathan Wylde, SPE, Head of Global Innovation, Clariant Oil Services

01 September 2014

Volume: 66 | Issue: 9

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