Robust Scale Dissolver Mitigates Mixed-Scale Issue in South China Sea
Authors: Carpenter Chris 
Published: November 2023

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 211187, “Tackling Mixed-Scales Issue in an Oil Field Using a Novel Robust Scale Dissolver,” by Nora Aida Ramly, Luky Hendraningrat, SPE, and Latief Riyanto, SPE, Petronas, et al. The paper has not been peer reviewed.

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The evaluation of a recently developed robust solid dissolver (RSD), from the laboratory phase through pilot deployment, is presented in the complete paper. Based on laboratory tests, the RSD can dissolve mixed scales completely in 24 hours at well temperatures while experiencing no incompatibility issues with production chemicals and all pumping and wireline components. The RSD was developed based on the total organic system that can prevent corrosion and is compatible with hydrocarbon. The RSD was piloted at oil Well 1 in Field PN and successfully removed mixed scales, allowing the well’s revival.

Introduction
Solid scale deposition is one of the most frequent flow-assurance issues both in subsurface and at the surface. The scale can be classified as organic (wax or asphaltenes), inorganic (calcites, sulphates, sulfides, halites, carbonates, and oxides), soap-related (naphthenates and carboxylates), gas-related (hydrates), or mixed scales. Scale occurrence, quantity, and severity mainly are determined by mineralogy, water chemistry, reservoir pressure and temperature, and the flow characteristics of the producing fluid in the well. Furthermore, scale formation is exacerbated by higher pH conditions and a higher water-cut environment, as would be expected in oil fields where water is to be injected for pressure maintenance.
The most common type of scales found in Malaysian oil fields are organic and inorganic scales. The operator’s previously deployed scale-dissolving chemical in its fields only could cater to a single type of scale treatment at a time, which was ineffective for dissolving mixed scales simultaneously. Another method is the use of a mechanical solution using a coiled tubing unit (CTU). Removal mechanically by CTU in tubulars is a successful method in removing hard barite scales, but the cost is high and the method requires several days of production deferment. An improved and cheaper mixed-scale removal approach was needed to clean out mixed-scale issues in more-challenging brownfields.
The RSD technology was developed for wellbore cleanout caused by mixed scale based on a stable microemulsion solution consisting of acid and solvent components. The solution was proposed to dissolve both organic and inorganic scales simultaneously in the near-wellbore area and tubing string of an oil well. The very small droplet size formed by the surfactant system and solvent is a significant advantage of using microemulsion and can allow penetration even in tight formations with small pore throats and promotes more-uniform surface coverage because of the increased interfacial area of the droplets. Previous studies have reported that the microemulsion can be pumped without causing a significant increase in pumping pressure.