ABSTRACT

In-situ oil sands water treatment systems (WTS) used to treat and recycle produced water to ultimately supply steam to the steam assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS) processes have noted failures associated with corrosion including erosion-corrosion, under deposit corrosion (UDC), fouling/scaling, and localized corrosion among others. Oil sands operators employ corrosion monitoring tools, chemical treatment, and/or material selections to solve integrity related issues. However, the unpredictable occurrences of serious corrosion issues related to the complex and constantly changing water chemistries make it difficult to choose the appropriate preventative and mitigation strategies. This is further complicated by the effects of operating conditions; such as temperature, pressure, and flow geometry.

This paper presents a study on the corrosivity of field produced water obtained from in-situ oil sands operators to UNS G10180 carbon steel. Rotating cylinder electrode (RCE) and rotating cage autoclave (RCA) systems were used as test methods. The susceptibility of the carbon steel to pitting was also evaluated using cyclic potentiodynamic polarization method. The findings indicated that corrosion rates were highly influenced by both water chemistries and operating conditions.

INTRODUCTION

Background

Alberta's oil sands reserves are estimated at 170 billion barrels with the majority of the oil (< 80 %) accessible only using in-situ extraction processes. Various in-situ extraction methods have been proposed and/or implemented including steam assisted gravity drainage (SAGD), cyclic steam simulation (CSS), toe-to-heel air injection (THAI) and vapor extraction (VapEx).1 Currently, CSS and SAGD are the predominant in-situ processes for oil sands production. The two processes require water for steam generation and subsequent injection into the oil sands reserve to lower the viscosity of the bitumen prior to removal. Typically, these methods require 2 – 3 barrels of steam (cold water equivalence) to produce one barrel of oil.2 Water treatment systems used to recycle produced water and/or make-up water for the production of steam used in SAGD and CSS processes have noted failures associated with erosion-corrosion, under deposit corrosion, microbially influenced corrosion (MIC) and fouling/scaling. These different types of failures have been documented in water treatment plants that process brackish or fresh water sources, and recycle produced water.3

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