Comparing Efficacy of Scale Inhibitors for Inhibition of Zinc Sulfide and Lead Sulfide Scales.

Abstract

A large independent operator in Mobile Bay, Gulf of Mexico was experiencing a buildup of common and exotic scales where the produced waters are commingled.The scale species encountered included barium sulfate, zinc sulfide, and lead sulfide.Traditionally, scale inhibitor chemistries have not been used in the past to inhibit these exotic sulfide scales in this region.This is due to some amount of belief within the industry that conventional inhibitors alone could not inhibit these scale species. Prior to the application of the scale inhibitor in the field, the platform's overboard water line required cleanout every two months due to scale buildup.Not a single cleanout has been necessary since a polymeric scale inhibitor has been applied downhole via continuous capillary injection for over one year. This paper presents the results of laboratory tests which were used to demonstrate how a polymeric scale inhibitor was identified and approved for inhibition of lead sulfide and iron sulfide, as well as the more common scales.The sulfide scale tests performed in an anaerobic dynamic tube-blocking test unit showed this inhibitor chemistry to be as effective as combined scale inhibitor/dispersant products. The paper then presents the field treatment results, which shows good agreement with the lab test results. Introduction Commingled brines present problems in the surface and subsurface due to ionic species forming insoluble mineral scale species.Barium sulfate (BaSO4) and calcium carbonate (CaCO[3]) are two of the most common mineral scales encountered in the oilfield and could be considered well-understood.However, zinc sulfide (ZnS) and lead sulfide (PbS) are less common, and require a slightly different approach to treatment.It has been suggested in the past that a special type of "novel" scale inhibitor is best for inhibiting zinc sulfide and lead sulfide scales[1].Additionally, there are a handful of commercial inhibitors which are sold as specialized sulfide scale inhibitors.The goal of this work was to compare the efficacy of one of these specialized sulfide scale inhibitors versus a proprietary product chemistry to determine the relative performance under the conditions of this Mobile Bay field. Whereas most ZnS/PbS scale inhibitor evaluations have relied on static bottle tests or field test data to determine[1,2,3,4], the tests described in this paper were performed using an anaerobic dynamic tube-blocking apparatus.There are distinct advantages to be gained with the ability to compare product efficacies before progressing to a field trial stage.The anaerobic tube-blocking tests more accurately simulate the dynamic environment where the scale inhibitor products would be used than static bottle tests.The differential pressure transducer detects very minor increases in differential pressure (DP), which indicates when scale has deposited in the test apparatus. This allows nucleation inhibition properties and dispersant properties of the scale inhibitor products to be more closely evaluated than in static bottle tests. Scale Inhibitor Products The main focus of this study was to compare the performance of a commercial sulfide scale inhibitor against a proprietary polymeric scale inhibitor.Product A is a commercially-available sulfide scale inhibitor.Products B through E were polymeric scale inhibitor products provided by chemical suppliers, who indicated the chemistries might be effective as zinc sulfide and lead sulfide inhibitors.Product F is a blend of polymers.Product G is a proprietary polymeric scale inhibitor which was readily available commercially.Table 1 provides a quick reference to the generic chemistry of each product.

Development of a Unique Organic Acid Solution for Removing Composite Field Scales

“… 11 Commonly, zinc and lead sulfides precipitated in downhole completion tools as control valves. 12 , 13 The drilling operations utilized barite (barium sulfate) as a weighting material for the drilling fluids, and during drilling operations, the mud invades the drilled formation with barite solids, and therefore, barium sulfate scale precipitated and damaged the drilled formation by reducing the rock porosity and permeability. 14 Strontium-based sulfate is a common scale with the production surface facilities and processing units.…”

“…Due to these controlling conditions for the scale precipitation, the location of scale is different based on the existing source and operation condition as the sulfate scales precipitated with the seawater injection system because of incompatibility of water sources and this is considered as a hard scale type due to its low solubility with acid . Commonly, zinc and lead sulfides precipitated in downhole completion tools as control valves. , The drilling operations utilized barite (barium sulfate) as a weighting material for the drilling fluids, and during drilling operations, the mud invades the drilled formation with barite solids, and therefore, barium sulfate scale precipitated and damaged the drilled formation by reducing the rock porosity and permeability . Strontium-based sulfate is a common scale with the production surface facilities and processing units .…”

A Novel Low-Temperature Non-Corrosive Sulfate/Sulfide Scale Dissolver

“…The locations of scale depositions differ due to temperature and pressure conditions. Lead and zinc sulfide scales are found to be deposited in the shallower part of the well completion, control valves, and in the subsurface safety control valves [13,14]. Sulfate scales were found to be deposited by the seawater injection operations, and such a scale is one of the hardest scales to be removed as it has low acid-solubility.…”

Deposition of Inorganic Carbonate, Sulfate, and Sulfide Scales on Antifouling Surfaces in Multiphase Flow

“…Previous research in the area of sulfide mineral scale prevention has predominantly focused on chemical inhibition, ,, or physical removal through acid chemical treatment combined with mechanical methods . As an alternative to batch injection or reactionary mechanical techniques, the use of antifouling coatings has been proposed as a way to drastically reduce the initial deposition and buildup of inorganic scales on surfaces. − This contribution investigates a number of proposed antifouling coatings with diverse physio-chemical parameters, variants of which are already implemented in downhole applications due to their high durability and fouling resistant properties.…”