Abstract
The perennial problem of identifying the “best” scale inhibitor is complicated by the wide diversity of operating conditions found in the field and the variety of available chemistries. To provide some guidance in selecting the proper scale inhibitor, a study was made of several scale inhibitors to map their limitations against common field conditions.
Seven scale inhibitors with different active chemistries were identified and assessed to determine their limitations in the following areas: performance against calcite and barite scale, thermal stability (inhibitor performance and physical properties after ageing), brine compatibility/calcium tolerance, and tolerance to dissolved iron.
Each product’s effectiveness as a scale inhibitor was assessed by dynamic scale loop (DSL) testing against calcium carbonate scaling and barium sulfate scaling. Thermally aged testing used samples of the product aged for 24 hours at temperatures ranging from 110 to 170°C before testing. Assessing the brine compatibility of the inhibitors required unaged products and brines of varying calcium levels to be tested over 24 hours at 90°C. Analyzing the effectiveness of each product in the presence of iron compared the minimum effective dosage (MED) required to inhibit scale in brine with and without the addition of iron.
Using the results of this test matrix, the authors identify which chemistries best apply to a given set of field conditions.
Introduction
It is known within oil and gas industry that correct experimental design to replicate the scaling conditions in the field is key to the correct selection of scale inhibitor and considerable effort has been expended in this direction.1,2,3
The impact of dissolved iron on inhibitor performance has been indicated previously for two generically different chemistries by Graham et al. who identified that even small levels of dissolved iron can have an a significant impact on scale inhibitor performance.4,5 Equally it is also understood that inhibitor chemistries will offer different levels of performance against different scale types.
In this work we present an assessment of seven different inhibitor chemistries to determine their limitations in the following areas:
• Scale inhibition against calcium carbonate scale
• Scale inhibition against barium sulfate scale
• Thermal stability (product performance and stability of physical properties (pH, specific gravity (SG), appearance) after ageing)
• Brine compatibility/calcium tolerance
• Tolerance to dissolved iron
