Development of Test Method and Environmentally Acceptable Inhibitors for Zinc Sulfide Deposited in Oil and Gas Fields

Abstract

Zinc sulfide (ZnS) is an exotic scale formed in the oil and gas fields, especially in HT/HP wells. It is relatively difficult to test ZnS formation and inhibition in the laboratory using traditional static jar and dynamic loop tests due to the oxidization during the test and its naturally ‘soft’ scale characteristic. Limited studies have been focused on ZnS and the detailed inhibition mechanisms are still unknown. In this paper, a newly developed stress test method has been applied to evaluate the performance and mechanisms of ZnS inhibition. Compared with the traditional test methods, it shows good reproducibility and provides a quick and effective way to evaluate the performance of inhibitors and information to understand the mechanisms of inhibition. More than 15 typical scale inhibitors, representing several different types, have been tested using this newly developed method. The ZnS scale inhibitors were classified as three types based on the inhibition mechanisms from this work: Type 1: Dispersion and nucleation inhibitors. These scale inhibitors showed nucleation and growth inhibition effect at low concentrations of sulfide and dispersion effect at high concentrations of sulfide. Type 2: Nucleation and growth scale inhibitors. These scale inhibitors inhibit nucleation and growth of ZnS formation, where the test can be stressed further. Type 3: Scale inhibitors with poor performance on ZnS inhibition. The turbidity and stress curve did not change obviously in the presence of scale inhibitors. This paper will give a comprehensive study of ZnS formation and inhibition, including scale prediction, development of test method and inhibitors, insight into the mechanism of ZnS inhibition and identification of environmentally acceptable inhibitors.

Mechanisms of Environmentally Acceptable Inhibitors for Zinc Sulphide Inhibition

“…Scaling of metallic or insulating walls in contact with hard water may create technical problems, including under-deposit corrosion, pipe or valve blockage, and, more importantly, unscheduled equipment shutdown. 1,2 The most common mineral scales formed from produced waters in the oil and gas industry are calcium carbonate and barium sulphate. Great efforts have been made to understand the conventional oilfield scale formation and inhibition.…”

“…14 - 16 Compared to conventional mineral scale deposits, zinc sulfide has received less attention over the years, possibly because of the challenges of studying zinc sulfide under laboratory conditions. 2 Zinc sulphide crystals often form a softer scale than conventional oilfield scales, which may not adhere to the surface of a test coil in the traditional tube blocking test rig. Furthermore, tiny amounts of zinc sulfide may be expected to form from field produced water chemistries, which also leads to a lower propensity for tube blocking.…”

“…2 Okocha (2010) studied the effect of zinc sulfide on the growth and dissolution of barium sulphate crystals using static jar tests under anaerobic conditions. 17 The morphology of barium sulphate and zinc sulphide crystals was examined in the presence and absence of scale inhibitor.…”

“…Wang and Chen (2012) developed a stress test method to evaluate the performance and mechanism of zinc sulphide inhibition. 2 Both these test methods are limited to 90°C, meaning that they could not be used to examine zinc sulfide formation and inhibition under the higher temperatures that may be experienced in the field. Dyer et al (2006) studied sulfide scales using both static jar tests and dynamic in situ filter tests and were therefore able to examine sulphide scale at elevated temperatures.…”

Mechanisms, New Test Methodology and Environmentally Acceptable Inhibitors for Co-deposition of Zinc Sulfide and Calcium Carbonate Scales for High Temperature Application

“…The formation of mineral scale is a persistent and expensive problem in oil and gas production. Scaling of metallic or insulating walls in contact with hard water may create technical problems including under-deposit corrosion, pipe or valve blockage and even more importantly, unscheduled equipment shutdown (Yang, et al, 2001;Wang, et al, 2012).…”