Carbonate Scale Formation on Steel Surfaces

Abstract

Abstract This study was concerned with scale deposition on heated steel disks under controlled laboratory conditions. Produced brines from fields in South and West Texas were used as the scaling solutions. These brines exhibited a wide range of salt concentration. A laboratory testing apparatus was developed. The main feature of the new apparatus is its ability to measure the skin temperature (i.e., the temperature at the brine-steel interface). A series of tests were made covering a temperature range of from 120 to 190°F. This temperature range represents a variety of field conditions, from surface to downhole. A quantitative measurement of calcium carbonate deposition vs temperature was obtained. Thirteen selected chemicals were tested for possible use as scale inhibitors. The selection was based on the properties that might affect scale deposition, such as dispersion, sequestration, interionic action, film formation ... etc. The inhibition of scale by the various chemicals used was found to vary considerably. Film-forming compounds in the presence of crude oil proved highly effective. The nature of the scale crystals and the influence of the additives on crystal habit modification was studied through microscopic examination and photomicrographs. X-ray studies were used to indicate the chemical nature of the scale. The experimental procedure and conditions under which scale is deposited were found to be of great importance. In view of the encouraging results, the field application of film-forming compounds as scale inhibitors is highly recommended.