Abstract

Soap deposits, which can manifest as emulsion soaps (carboxylates) or hard deposits (naphthenates), are an increasingly recognized cause of some unique flow assurance and crude marketing problems in oilfield processes.This paper illustrates the physical and chemical drivers for the generation of soap scales in a number of differing and challenging production system environments.Mitigation options for the successful treatment of soap scales are also discussed. Where possible, data presented in this paper are taken from field trials in order to illustrate these drivers and the impact of successful mitigation strategies.

An understanding of the key fluid characteristics allows pre-screening of fluids from new field developments that are likely to develop naphthenate/soap deposits and allows diagnosis ofthe likely soap scaling problems. The critical fluid characteristics required for the generation of naphthenate soaps are different from those required for generation of carboxylate soaps.An empirical approach to predicting the degree of risk for soap generation, based on oil and produced water properties, can be adopted, although there are knowledge and data gaps that increase the uncertainty of this approach.

Physical parameters, such as pressure, are known to influence soap generation. However, other physical parameters that are key in the design and operation of an oil-field process can also influence the soap severity. These parameters include temperature, shear, electrostatic fields, water cut and fluid-fluid incompatibility; examples of each are discussed. This information can be used in the design stages of an oil-field process where engineers must think beyond the conventional process designs.

Despite the fact that the impact of a soap problem can be considerably reduced by adjustment of physical design and operating parameters, chemicals are usually required to provide complete mitigation of soap. Chemical mitigation (acid and non-acid) guidelines are discussed with field examples and the need for a chemical management and monitoring programme.

Introduction

Soap solids are formed when metals present in the reservoir water react with the napththenate or carboxylate groups to form salts (or soaps), which are generally sodium or calcium salts. These salts have been known to occur in a number of forms in the oilfield production system, including:

  • Dissolved salts that can and do affect the sales value of the crude by giving increased metal ion contents (e.g. calcium).

  • Viscous emulsions from wells and interfacial emulsion pads in separators, which hinder efficient oil-water separation and can become waste sludges/slops in Crude Oil Terminals.

  • Hard, solid scale deposits that restrict production render controls systems inoperable and cause discharge water and export oil qualities to deteriorate.

Recognition of soap scales in production systems is becoming increasingly common.Such materials if not properly identified, understood and handled, will reduce the efficiency of a number of critical oilfield operational activities.These activities include oil dehydration, fluid desalting, produced and waste water treatment and disposal, oil storage and export.

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