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.
Discovered in 1991 and located approximately 130 miles south of New Orleans, the Ewing Bank 873 (EW 873) field is an offshore mature field in the Gulf of Mexico that produces hydrocarbon from unconsolidated sandstone reservoirs of Middle-Upper Pliocene age. Most wells within the field were completed using cased-hole gravel packed completions, and field production began in 1994.Throughout the production cycle of the EW 873 field, wells such as Well A-04 had experienced severe production impairment from near-wellbore (NWB) formation damage, as well as tubular buildups from barium sulfate (BaSO 4 ) scale caused by incompatible mixing between formation water and biocide inhibited seawater that broke through from an offset injection well. While mechanical techniques such as coiled tubing-conveyed hydroblasting have been commonly used to remove BaSO 4 tubular scale, the success of these techniques largely depends on the nature and magnitude of the BaSO 4 , as well as effective operational planning.This paper presents the five-step engineered approach of the coiled tubing hydroblasting intervention that mechanically removed as much as 3,150 ft. measured depth (MD) of BaSO 4 tubular scale from Well A-04. Additionally, the paper presents the tools that were utilized throughout the intervention and the laboratory and field methods that were applied to characterize the BaSO 4 . With NWB formation damage and production impairment already established to be a problem on Well A-04, the successful coiled tubing-conveyed hydroblasting intervention created an opportunity to effectively conduct a chelant-based hydrofluoric (HF) acid treatment that increased oil production by as much as 305% on the well (Sopngwi et al. 2014).
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