No abstract

No abstract

No abstract

Significant advances in acidizing chemistry have led to the introduction of sequestering agents, such as hydroxypolycarboxylic acids, followed by chelating agents, to mitigate precipitation reactions. The initiative to obtain fluids with an improved environmental footprint has led to the redesign of treatment fluids to possess distinct advantages, such as stability at higher temperature, broader pH activity, and stronger complex formation. In the area of hydrofluoric (HF) acidizing chemistry, the conceptualization of the unique HF acid reactions on clays and silica surfaces—namely, kinetic controls over the so-called primary, secondary, and tertiary reactions—has facilitated fluid designs that can handle such varied reactions. The work presented here describes the development of a new acidizing fluid containing an environmentally relevant chelating agent and an aminpolyocarboxylic acid. The chelating agent is fully biodegradable, according to the Organization for Economic Co-operation and Development (OECD) protocols, is stable in fluid media from pH 1 to 7 and at high temperatures, and stabilizes the dissolved ions during an acidizing treatment. In HF acidizing, the chelant performance has been tested at 0.6 mol/L and HF acid concentrations from 0.5 to 2%, pH of 2.5 to 4, including a stabilizing agent to mitigate the precipitation of fluorosilicates or fluoroaluminates, and is effective in temperature ranges from 200 to 300°F. Laboratory tests show it to be effective in maintaining in solution dissolved aluminum (3000 to 10 000 mg/L), calcium (5000 mg/L), and iron (6000 mg/L). The use of nuclear magnetic resonance (NMR) spectroscopic analysis revealed additional dissolved-fluoride-containing species that has not been previously reported. Moreover, the chelating agent can also be used when stimulating carbonate rocks in concentrations from 0.2 to 0.6 M with a pH of 1 to 4 and is effective from 125 to 350°F. The representative pore volume breakthrough (PVbt) curves provide an indication of the distinct reactivity of this chelant.

No abstract

An existing limitation of chelant-based fluids available for sandstone acidizing with hydrofluoric acid (HF) is the presence of sodium in the concentrate of the aminopolycarboxylate fluid, which is common in all chelating agents soluble below pH 3.5. The presence of sodium complicates stabilization of the fluid during acidizing processes because of the myriad of chemical reactions that can impact the outcome of a treatment. The use of chelating agents has expanded the temperature range as well as the type of clay minerals that can be exposed to an HF fluid; however, limitations still exist. Core flow testing at 360°F and corrosion testing from 265 to 360°F were conducted. Flow tests were performed using outcrops of two types of sandstones and inductively coupled plasma (ICP) analysis was conducted to elucidate the ionic composition of the spent fluid. Results reported stem from core flow testing with glutamic acid diacetic acid (GLDA) containing HF at very high temperatures (360°F). To encompass a broad range of mineral composition, two types of sandstone cores were employed-heterogeneous (Bandera, 65% quartz) and clean (Leopard, 95% quartz). Corrosion inhibition of the GLDA/HF fluid for use with coiled tubing (CT) was achieved up to 320°F, employing varying classes of inhibitors. The GLDA/HF fluid exhibited lessened corrosion tendencies and could be inhibited for at least 6 hours at 360°F for drillpipe (mass loss rates of 0.025 to 0.05 in./ft 2 were obtained).The presence of sodium in GLDA/HF could be managed, leading to effective permeability improvement of the Bandera core, while the Leopard core underwent a decrease in overall permeability; this latter observation was attributed to the formation of metal fluorides. Neither the presence of CaCO 3 in the Bandera substrate or the use of KCl brine substituting for the usual NH 4 Cl led to permeability impairment. The overall results indicated that 1% HF and 0.6 M GLDA with an auxiliary agent could circumvent the expected problems associated with HF acidizing and modification, volume minimization, or elimination of preflushes. The use of the GLDA chelant facilitates, when using CT to deliver fluid to hot zones (which can be susceptible to formation damage if aggressive fluids based on HCl or formic acid are used, or if acetic acid is employed), could be jeopardized because of the difficulties inhibiting the corrosive effects of HF, HCl, formic, or acetic blends.

The Ewing Bank 873 (EW 873) Field is an offshore mature field in the Gulf of Mexico that produces hydrocarbon from Pliocene stacked turbidite sands. Wells in the EW 873 Field have experienced production impairment from formation damage, such as aluminosilicates, fines, and scale, including calcium carbonate (CaCO3) and barium sulfate (BaSO4). This paper discusses the results of the successful application of a differentiated chelant-based hydrofluoric (HF) acid to remove formation damage and enhance oil production (by as much as 305%) from Well A-04 in the EW 873 Field. Additionally, the paper presents the chemical analyses of the acid flowback as well as the methods used to characterize the formation damage. More importantly, the paper also focuses on the research efforts that led to the development and successful application of the differentiated chelant-based HF acid. Throughout the research, analytical experiments and corefloods were performed with different acid formulations on cores that contained acid-sensitive clays, CaCO3 and BaSO4. Two formulations contained alpha-hydroxycarboxylic (a-HCA) HF acids, and other formulations contained chelants and chelant HF acids, which were both based on an aminopolycarboxylic acid (APCA). The APCA/HF acid proved to be the most effective formulation, as it achieved the highest permeability increase (relative to brine) and dissolved ions while mitigating precipitation. Furthermore, the APCA/HF acid is biodegradable, and compatibility and corrosion testing indicated that it is compatible with the produced oil samples of Well A-04 and it exhibits low corrosion loss (< 0.05 lbm/ft2) when applied with a chosen corrosion inhibitor on 13-Cr metallurgy, respectively. The development of this differentiated APCA/HF acid highlights the potential of performing successful acid jobs where complex mineralogies, such as CaCO3 and BaSO4, are present.

No abstract