A Novel Low-Temperature Non-Corrosive Sulfate/Sulfide Scale Dissolver

Abstract

The oil and gas production operations suffer from scale depositions. The scale precipitations have a damaging impact on the reservoir pores, perforations, downhole and completion equipment, pipeline network, wellhead chokes, and surface facilities. Hydrocarbon production possibly decreased because of the scale accumulation in the well tubular, leading to a well plugging, this requires wells to be shut-in in severe cases to perform a clean-out job. Therefore, scale deposition is badly affecting petroleum economics. This research aims to design a scale dissolver with low cost, non-damaging for the well equipment and has a high performance at the field operating conditions. This paper presents a novel non-corrosive dissolver for sulfate and sulfide composite scale in alkaline pH and works at low-temperature conditions. The scale samples were collected from a production platform from different locations. A complete description of the scale samples was performed as X-ray diffraction (XRD) and X-ray fluorescence (XRF). The new scale dissolver was prepared in different concentrations to examine its dissolution efficiency for the scale with time at low temperatures. The experimental design studied the solid to fluid ratio, temperature, solubility time, and dissolution efficiency in order to achieve the optimum and most economic performance of solubility in terms of high dissolution efficiency with the smallest possible amount of scale dissolver. A solubility comparison was performed with other commercial-scale-dissolvers and the corrosion rate was tested. The experimental work results demonstrated the superior performance of the new scale dissolver. The new scale dissolver showed a solubility efficiency of 91.8% at a low temperature of 45 °C and 79% at 35 °C. The new scale dissolver showed a higher solubility ratio for the scale sample than the ethylenediaminetetraacetic acid (EDTA) (20 wt. %), diethylenetriamine pentaacetic acid (DTPA) (20 wt. %), and HCl (10 wt. %). The corrosion rate for the new non-corrosive dissolver was 0.01357 kg/m2 (0.00278 lb./ft²) which was considered a very low rate and non-damaging for the equipment. The low corrosive effect of the new dissolver will save the extra cost of adding the corrosion inhibitors and save the equipment from the damaging effect of the corrosive acids.

Barium Sulfate Scale Removal at Low-Temperature

“…The high pH scale dissolvers will not damage the well tubular and equipment as the corrosion rate is low. At the same time, high pH solutions will save the additional cost that is commonly applied for the scale inhibitors and intensifiers [31,32]. A study was performed to provide a scale dissolver with a 12.5 pH value for removing sulfate and/or sulfide scale types by employing specific concentrations of ethylenediamine, nitrilotriacetic acid (NTA), and chloroacetic acid [33].…”

From initial treatment design to final disposal of chelating agents: a review of corrosion and degradation mechanisms

“…A new sulfate scale dissolver composed of ethylenediamine, NTA, EDTA, chloroacetic acid, and a surfactant with a pH of 12.5 showed a corrosion rate of 12.7 mmpy (0.014 lb ft −2 ) at 90 °C (194 °F) and 6 h of testing. 75 A 0.4 M DTPA in presence of 1 vol% corrosion inhibitor and mutual solvent yielded a corrosion rate of 0.9 mmpy (0.001 lb ft −2 ) (N80) during an iron sulfide scale treatment process at 65 °C (150 °F). 76 Luo et al studied a DTPA–sodium polyacrylate blend (pH = 12) for the dissolution of barite and evaluated the blend's corrosion performance at 90 °C (194 °F).…”

Development of a Unique Organic Acid Solution for Removing Composite Field Scales

“…Another recent research was executed and provided a chemical dissolver with a 12.5 pH value for composite sulfate/sulfide scale removal at low temperatures, and the results showed scale solubility efficiencies of 91.8% at 45 °C and 79% at 35 °C. 30 …”

“…Calcium sulfate is a scale type that was found to have low solubility with high pH dissolvers . Also, dissolvers that have low pH will increase the tubular corrosion and therefore damage the facilities’ integrity. , Recent research studies − are directed to provide chemical dissolvers with high pH to sustain the well downhole and surface equipment, processing units, and facilities; also, this will save the corrosion inhibitor and intensifier cost that is commonly added to the treatment operations for low pH dissolvers. , Ahmed et al added tetrakis hydroxymethyl phosphonium salts (THPS) to ethylenediaminetetraacetic acid (EDTA) to formulate a slightly alkaline chemical solution with about pH value of 8. Another recent research was executed and provided a chemical dissolver with a 12.5 pH value for composite sulfate/sulfide scale removal at low temperatures, and the results showed scale solubility efficiencies of 91.8% at 45 °C and 79% at 35 °C …”

“…Another recent research was executed and provided a chemical dissolver with a 12.5 pH value for composite sulfate/sulfide scale removal at low temperatures, and the results showed scale solubility efficiencies of 91.8% at 45 °C and 79% at 35 °C. 30 The chemical removal for scale precipitations is a common method for descaling operations in the oil and gas industry that utilized various organic and inorganic solutions that depends mainly on the scale chemical composition for the chemical design of the dissolver. 33 Surfactants can be used to remove the hydrocarbon layer that covered the scale precipitations, and therefore, the dissolver solubility increased as there is more contact with the scale body after removing this layer of hydrocarbon.…”