The Efficiency of a DTPA-Based Solvent in the Dissolution of Barium Sulfate Scale Deposits

Abstract

This paper describes kinetic experiments to determine the rate at which Ba ions are mobilized from crystalline barium sulfate into aqueous solution by a solvent in which the active ingredient is a strong chelating agent for Ba ions (DTPA - diethylene triamine pentaacetic acid). The experiments define the temperature dependence and hence the activation energy of the dissolution process, the surface area dependence and most importantly the dependence on the concentration of the DTPA in solution. In a 0.05M DTPA solution the dissolution rate of barium sulfate is highly temperature dependent with an activation energy of 45kJ mol-1. This value suggests that the rate is controlled by the desorption of a Ba-DTPA surface complex. Surface complexation is further identified as the key to barium sulfate dissolution by the observation that over the concentration range 0.5M to 0.05M DTPA the initial dissolution rate is inversely related to the DTPA concentration. The activation energy remains unaltered but the absolute dissolution rate is increased. In other words, a 0.05M DTPA solution is more efficient as a solvent than a 0.5M solution. This unexpected result is interpreted in terms of a passivation of the barium sulfate surface by the formation of a surface complex layer at high DTPA concentrations. Introduction During secondary oil recovery from offshore oil-bearing reservoirs, pressure is maintained by injecting the well with seawater. A common problem with this procedure is that the formation water in the reservoir often contains high concentrations of alkaline-earth metal ions (Ba2+, Ca2+ and Sr2+). When the injected seawater, which contains sulfate ions (SO42-) comes into contact with the formation water in the region of the wellbore, the resulting barium, calcium and strontium sulfate precipitation blocks the production tubing and reduces the porosity of the surrounding reservoir rocks. This is a world-wide problem and causes considerable production losses. An associated problem is that the formation water may also contain a significant concentration of radioactive isotopes (uranium and thorium decay products) which also precipitates as the sulfate and may render the scale sufficiently radioactive to be a potential health problem. One possible approach to avoid the scaling problem is to attempt to remove the sulfate from the seawater by reverse osmosis prior to injection. However, the large volume of seawater to be treated would require significant capital expenditure. P. 773

Mechanisms of Surface Precipitation and Dissolution of Barite: A Morphology Approach

“…Most dissolution studies have employed solid particles stirred in water (10,12) or a chelating agent (4,13,14), with kinetic information inferred from changes in the chemical composition of the bulk solution, measured as a function of time. Surface complexation is a crucial step of initial dissolution of barite.…”

“…usc.edu. (13,17). This paper presents the results of experiments in which well-formed synthetic barite was reacted with DTPA (diethylenetrinitrilopentaacetic acid) at atmospheric pressure and temperature of 60°C.…”

A Novel Delivery Method for Combined Scale Dissolver and Scale Squeeze Treatments in Non-Isolated Subsea Wells

“…Slow dissolution rates and the need for temperature to enhance performance are key factors for sulphate dissolvers. Commercial sulphate scale dissolvers such as the product used in this case are normally based on an amino-carboxylic acid chemistry such as EDTA and DTPA which when combined with an activator have shown successful dissolution of mixed sulphate scales where applied appropriately (Bakken 1996;Benson 1997;Putnis 1995;Klepaker 2002;Kelly 2005;Jordan 2002). As already mentioned, factors that impact the amount of scale dissolved include test temperature, contact time, formulation pH, solution diluent, addition of mutual solvent and scale particle size (Jordan 2012).…”

Inhibition of growth in solid solution–aqueous solution systems by non-incorporating impurities

“…(8) it is assumed, as in the case of Eq. (5), that the degree of coverage of the surface by the impurity is proportional to its concentration in the aqueous solution (Eq. (4)).…”

“…Many industrial activities also require the usage of chemical compounds that inhibit mineral formation. For instance, phospho nates have been used to prevent undesirable barite mineralization in marine oil and gas wells where the concentrations of sulphate and barium ions are high [5][6][7]. In a similar vein, phosphate-based inhibitors and phosphonates have been employed to avoid calcite formation in pipes, cooling and boiling water systems, and desalina-E-mail address:cmpina@geo.ucm.es.…”