Thermal Stability of Various Chelates that are used in the Oilfield and Potential Damage Due to their Decomposition Products

Abstract

Chelating agents are used to remove various inorganic scales, including sulfates and carbonates. They are also used as stand-alone stimulation fluids and as iron control agents during acidizing treatments. The main chelating agents used in the field, include: ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), N-(hydroxyethyl)-ethylenediamineteriaacetic acid (HEDTA), and recently, L- glutamic acid-N, N diacetic acid (GLDA). One of the concerns with these chelates is their thermal stability at elevated temperatures. A few studies examined the thermal stability of these chelating agents, and the impact of thermal degradation products on permeability. The objectives of the present study are to: 1) Examine the thermal stability of several chelating agents and their salts up to 450°F, and 2) assess the effect of thermal decomposition products on the permeability of carbonate and sandstone cores with different initial permeabilities. We prepared solutions (0.4 to 0.6 M) of HEDTA, GLDA, NTA, EDTA and their salts. The solutions of these chelates were heated at various temperatures and times (2 to 12 hrs.). The concentration of chelate was determined using a new analytical technique that was based on titration with FeCl3. The products of thermal decomposition of chelates were determined using MS technique. Core flood tests were conducted on Berea sandstone and Indiana limestone to determine the effect of thermal degradation products on the permeability of these cores. Coreflood tests were conducted at 325°F and 3 cm3/min. Most chelates decomposed at temperatures greater than 350°F. Among monovalent salts, potassium salt was found to be the most stable one. Chelates with two nitrogen atoms were more stable than those with one nitrogen atom. For example, diammonium salt of EDTA is more stable than diammonium salt of GLDA. Analyses of chelate solutions after heating using MS technique highlighted that the decomposition products included: iminodiacetic acid, formic acid, and α-hydroxy acids. Results of the coreflood indicated that some of the thermal decomposition products can cause formation damage. This paper will summarize the results obtained, and explain how chelates can be used to improve field treatments, especially at high temperatures.

Stimulation of High Temperature SAGD Producer Wells Using a Novel Chelating Agent (GLDA) and Subsequent Geochemical Modeling Using PHREEQC

“…The chelate concentration was measured by titration with a ferric chloride solution (Sokhanvarian et al 2012). Filtration with 1 m pore size filter paper was used to separate solid particles.…”

“…These products are glutaric and iminodiacetic acids (Fig. It should be also noted that hydroxyglutaric and iminodiacetic acids were previously identified as a decomposition products for H 4 GLDA (Sokhanvarian et al 2012). Peak for retention time 17.33 minutes wasn't fully interpreted but it most probably presents heavy hydrocarbons.…”

“…As it was explained previously, sodium hydroxide was used to precipitate Fe(OH) 3 . Sokhanvarian et al (2012) reported that at 400°F for 6 hours of soaking time stability of the NaGLDA is less than 30 %. The initial concentration of the GLDA in the treatment prior to dilution was 20 wt% (Table 2).…”

“…Reyes et al (2013) tested an aminopolycarboxylic acid (APCA) which was found to be a biodegradable chelating agent. (Sokhanvarian et al 2012) examined the thermal stability of GLDA and other chelates at different temperatures and soaking time. (Sokhanvarian et al 2012) examined the thermal stability of GLDA and other chelates at different temperatures and soaking time.…”

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

“… 42 Ethylenediaminetetraacetic acid (EDTA), hydroxyethyl ethylene diamine triacetic acid (HEDTA), hydroxyethyl iminodiacetic acid (HIDA), glutamic acid di-acetic acid (GLDA), diethylenetriamine pentaacetic acid (DTPA), nitrilotriacetic acid (NTA), and methylglycinediacetic acid (MGDA) are considered common examples for the chelating agents in field descale operations. 43 A study was performed to evaluate the dissolution efficiency for DTPA (20 wt %) with a catalyst (9 wt % potassium carbonate) to dissolve the pyrite (FeS 2 ) scale precipitation, and results showed that 85% of the scale was dissolved at 70 °C and a time of 48 h. 44 , 45 Nitrilotriacetic acid (NTA) is an additional example of the chelating agents that provides a high biodegradability. 46 However, using the chelating agents in the descale treatment is not considered the optimum solution as they are expensive chemicals and further experimental work is needed to determine the optimum pH, solution concentration, treatment time, and thermal stability.…”