Development of Environmental Friendly Iron Sulfide Inhibitors for Field Application

Abstract

Abstract The inhibition of iron sulfide mineral scale formation in oil and gas production is notoriously difficult. High concentrations of scale inhibitors are always needed to provide limited inhibition performance. In addition, it is extremely difficult to test the iron sulfide formation and inhibition in the laboratory. In this paper, a novel iron sulfide test method has been developed to test the performance of iron sulfide inhibition. Compared with the traditional static jar test and dynamic loop test, this novel developed test method shows good reproducibility and provides a quick and effective way to evaluate the performance of iron sulfide scale inhibition. An environmentally friendly iron sulfide scale inhibitor has been developed based on this novel developed test method. It provided good performance on iron sulfide inhibition in synthetic field water. The mechanism of iron sulfide inhibition will be addressed. This paper will give a comprehensive study of iron sulfide formation and inhibition, including iron sulfide prediction, development of test method and development of inhibitors for field application. Introduction 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 pipe or valve blockage, under-deposit corrosion, and even more importantly, unscheduled equipment shutdown [1]. Over the past few decades, great efforts have been made to understand the conventional oilfield scale formation and inhibition, such as CaCO3, BaSO4 and CaSO4. Compared to these conventional mineral scale deposits, iron sulfide has received less attentions. Three of the major reasons are:Some iron sulfide crystals often form a softer scale than calcium carbonate. This scale may not always block tubing to the same degree that other mineral scales do. Thus, it may be seen as less of a problem than other mineral scales [2];Iron sulfide is much more difficult to study in the laboratory than other common mineral scales, where keeping the system oxygen free and the reproducibility of the iron sulfide test are two major challenges.Iron sulfide is present in several crystalline forms that have different sulfur to iron ratios. These different crystalline forms have different solubility in mineral acids, which make the research complex [3]. These challenges may deter the progress of research on iron sulfide scale formation and inhibition. Iron sulfide scale is thought to be deposited by microbial enhanced corrosion or derived from the reaction of iron oxide from corrosion and hydrogen sulfide, a by-product of sulphate reducing bacteria (SRB) metabolism. Another unexpected source of hydrogen sulfide is acid treatment [3]. Aksnick and Engen [4] found iron sulfide scale in well tubular following acid treatments of deep sour gas wells. Recently, sulfide scales have been encountered in more sour reservoirs and deeper wells and more attention has been paid on the study of iron sulfide. In the work reported herein, a novel iron sulfide test method has been developed to test the performance of iron sulfide inhibition. Compared with the traditional static jar test and dynamic loop test, this novel developed test method shows good reproducibility and provides a quick and effective way to evaluate the performance of iron sulfide scale inhibition. An environmentally friendly iron sulfide scale inhibitor has been developed based on this novel developed test method. It showed good performance on iron sulfide inhibition in synthetic field water. The mechanism of iron sulfide inhibition will be addressed.