Understanding the Mechanisms of Halite Inhibition and Evaluation of Halite Scale Inhibitor by Static and Dynamic Tests

Abstract

Abstract The inhibition of halite mineral scale formation in oil and gas production is notoriously difficult. High concentrations of halite inhibitors always provide limited inhibition performance. In addition, it is extremely difficult to test halite formation and inhibition in the lab. In this paper, the dynamic halite loop has been developed to test halite formation and inhibition. Halite formation and inhibition were tested under both traditional static conditions and newly developed dynamic conditions. The results showed inconsistencies based on static jar tests and dynamic loop tests. The possible mechanisms of halite inhibition are discussed. The following conclusions have been drawn:Compared with the traditional static jar test, dynamic halite loop tests are more representative of halite formation in the field conditions and showed good reproducibility.The newly developed scale inhibitor demonstrated dynamic inhibition performance towards halite formation. Efficiency loop tests showed that the minimum inhibitor concentration (MIC) is less than 200ppm to inhibit halite formation effectively under the test conditions. Introduction Halite scale is one of the 'exotic scales' found in the oil and gas industry. It deposits when field water condenses due to gas generation during production. In addition, it occurs when temperature is reduced, where the saturation of salt in field water drops. In Northern German gas reservoirs, the precipitation of salt from the reservoir water is observed to an increasing extent as recovery progresses [1]. Precipitation of halite can occur near wellbore as well as in the wellbore, if saline groundwater is present during the operation of natural gas storage aquifers and reservoirs[2].In addition, halite was found when the reservoir fluids cool down in an asset producing oil with a water cut between 1% and 5% and a TDS of 350000mg/l. The resulting halite scale reduces the wellbore performance drastically and causes a significant decrease in production rate, all the way to complete blockage of the flow paths and ultimately the abandonment of wells. In order to remove salt deposits as well as prevent the precipitation of salt in the zone immediately surrounding the well, fresh water treatments are performed at regular intervals during production operations [1]. This method is successfully used in oil and gas production. However, large quantities of fresh water bring operational difficulties. In addition, halite deposits quickly between the intervals of the fresh water treatments. Chemical treatment is an alternative approach to inhibit halite formation. High concentrations of the conventional nitrilotriacid based halite inhibitors provide limited performance and the mechanism of halite scale formation is still unclear [3]. In addition, it is extremely difficult to test halite formation and inhibition in the laboratory. The reproducility is a considerable challenge for the halite evaluation in the laboratory.