Abstract

This paper investigates the application of halite inhibitors and the mechanisms associated with salt formation and inhibition. Several new chemistries (two inorganic compounds and one organic nitrogen-based product) have been identified which provide improved halite inhibition. Their inhibition performance was studied and compared with commercially available inhibitors.

Salt deposition in high salinity brines can cause blockages to production and process systems requiring remedial action, often on short notice. Current commercial halite inhibitors are only effective at high concentrations (250 - 5,000 ppm). Therefore, a more efficient salt inhibitor would need to reduce both treatment level and production downtime.

The inhibition performance of three new chemicals and two commercial products were evaluated under static conditions along with performance assessment after aging. Both sea salt and pharmaceutical-grade sodium chloride were used in the tests. All three new chemicals showed improved inhibition efficiency over the two commercially available products. The retention property for one of the three new chemicals was evaluated using two different core materials. The test results showed a satisfactory amount of adsorption under favourable pH conditions. Core floods using field core materials were conducted to evaluate the chemical squeeze packages. No formation damage was observed, both oil and brine permeabilities have recovered following the chemical treatments.

A lower dosage (10-50 ppm) was required for the new chemical as compared with conventional treatment levels. The lower treatment level provides the potential to reduce cost, treatment intervals and production downtime. Moreover, there is the opportunity for the new product to be batch squeezed into the reservoir, providing prolonged protection against salt deposition.

Introduction

Sodium chloride is the most common salt present in formation waters. For high salinity brines (>200,000 mg/L) or formation waters containing sodium chloride close to saturation, there is potential for sodium chloride deposition (halite) during production due to the cooling of the reservoir fluids. Salt deposition downhole may cause substantial well productivity impairment and culminate in total flow blockage. Like any other type of scale precipitation, the halite deposition can bridge in the tubing, block the flowline and result in production decline. Even in relative low water-cut wells, dramatic halite buildup is still experienced in some parts of the world due to rapid salt deposition.

Although salt deposition is generally easier to remove than other type of scales by washing with fresh or low-salinity water periodically, frequent treatments necessitate well intervention and cause significant production deferment. This is further complicated with the availability of fresh or low-salinity water in some areas of the world due to the very large volume required during wash treatments. These issues necessitate preventative measures through chemicals with halite inhibition properties. However, the current commercial available halite inhibitors are only effective at high concentrations (>250 mg/L). This high MIC (Minimum Inhibitor Concentration) requires high dosage in continuous injection applications. When the same chemistry is used in squeeze applications, the squeeze life is often short due to the high MIC and the poor retention characteristics of the inhibitors.

To address these problems and limitations of the current available chemistries associated with salt removal, inhibition, and to improve the lifetime of a squeeze treatment, a R&D project was initiated to develop new chemistries and technologies to provide improved halite inhibition. The mechanisms of halite formation and inhibition were studied in detail. Various morphology changes following the addition of different halite inhibitors were recorded with the assistance of microscopic pictures. Based on this preliminary mechanistic overview of halite formation and inhibition, three new chemistries have been developed which have shown much improved inhibition efficiencies against the current commercial available chemistry under static field conditions.

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