In this paper, we will describe the development and testing of hydroxyaminocarboxylic acid chelating agents (HACA) as components of matrix acidizing formulations for stimulating carbonate formations. The pioneering work of Fredd and Fogler1 demonstrated that organic acids and chelating agents have unique attributes that lend themselves to efficient production of wormholes in many acidizing situations. We have applied the techniques for determining transport and reaction kinetics to stimulation fluids containing the hydroxy amino chelating agents. Linear core flood tests were used to study wormhole formation. Rotating disk tests with marble samples were employed to elucidate the kinetics and mechanisms of the dissolution processes over a temperature range of 20°C to >100°C (65 to >200°F).
Both HACA chemicals studied, that is, hydroxyethylethylenediaminetriacetic acid (HEDTA) and hydroxyethyliminodiacetic acid (HEIDA) produced wormholes in limestone cores when tested at 150°F. However the efficiency and capacities differ. Because these chemicals have high solubility in the acidic pH range, it was possible to test acidic (<ph a="" acids="" agents.="" allowed="" an="" and="" as="" at="" both="" by="" coefficients="" complexing="" determine="" different="" diffusion="" disk="" efficiency="" formation="" formulations.="" function="" have="" hler="" measure="" mineral="" of="" overall="" p="" parameters="" properties="" pump="" rate="" reaction="" rotating="" solutions="" surface="" temperatures.="" tests="" the="" these="" to="" us="" used="" vs.="" well="" were="" wormhole="">
Hydroxyaminocarboxylic acids (HACA) including hydroxyethylethylenediaminetriacetic acid (HEDTA) and hydroxyethyliminodiacetic acid (HEIDA) possess some unique chemical characteristics. The most significant attribute of these chemicals is the very high solubility of the free acids in aqueous solutions. In addition, HEIDA is very biodegradable. Other conventional chelating agents, such as ethylenediaminetetraacetic acid (EDTA) become insoluble in acid at pH values < about 4.0 and EDTA is essentially non-biodegradable. The unusual characteristics of the HACAs have facilitated the formulation of unique acidizing and scale removal systems that are being employed for cleaning and stimulating oil and gas wells. We have presented discussions of high-capacity iron-control formulations in SPE 632422 and provided descriptions of novel scale removal formulations in SPE 650273.
The current study describes a completely new family of matrix stimulation fluids based on HACA chemicals, which have a unique ability to be tailored to specific formation condition. Because of the high acid solubility of HACA chemicals, formulations containing mineral acids and organic acids, as well as high pH fluids have been produced. A major application will be stimulating high temperature formations where mineral acids cannot be pumped fast enough to produce wormholes unless they are retarded by formation of emulsions. In this paper, the low temperature data will be presented; high temperature data will be published at a later time. In addition, these new fluids will not require iron control agents to be added (they are effective iron complexers), and are easily inhibited to high temperatures (> 300°F) using minimal amounts of corrosion inhibitors. Based on similar work with EDTA, the formation of acid sludge is not expected to be as significant as that observed with conventional acid stimulation systems.
The experimental program included tests to determine the kinetic parameters for dissolution of calcite using the rotating disk (RD) methods, and for determining the extent of wormhole formation using core flood tests.