In situ decarboxylation of acetic and formic acids in aqueous inclusions as a possible way to produce excess CH4. Issue 3 (12th March 2013)

• Record Type: Journal Article
• Authors: Ong, A.; Pironon, J.; Robert, P.; Dubessy, J.; Caumon, M.‐C.; Randi, A.; Chailan, O.; Girard, J.‐P.
• Is Part Of: Geofluids. Volume 13:Issue 3(2013:Aug.)
• Page Start: 298
• Page End: 304
• Publication Date: 2013-03-12
• Subjects: acetic acid -- decarboxylation -- fluid inclusions -- formic acid -- fused silica capillary capsules -- Raman spectrometry; Hydrogeology -- Periodicals; Sedimentary basins -- Periodicals; Fluids -- Migration -- Periodicals; Groundwater flow -- Periodicals; Geothermal resources -- Periodicals; Fluid dynamics -- Periodicals; Earth -- Crust -- Periodicals; 551.49
• DOI: 10.1111/gfl.12026
• Languages: English
• ISSNs: 1468-8115

Abstract

Abstract: Accurate reconstruction of diagenetic P‐T conditions in petroleum reservoirs from fluid inclusion data relies on valid measurements of methane concentration in aqueous inclusions. Techniques have been developed (Raman spectrometry) to provide sufficiently accurate data, assuming measured methane concentration has not been modified after aqueous inclusion entrapment. This study investigates the likelihood that organic acids derived from petroleum fluids and dissolved in formation water might suffer decarboxylation upon postentrapment heating within the fluid inclusion chamber, thereby generating excess CH4 in the inclusions. Four different experiments were conducted in fused silica capillary capsules (FSCCs), mimicking fluid inclusions. The capsules were loaded with acetic (CH3 COOH) or formic (HCOOH) acid solution and were heated to 250°C for short durations (<72 h) in closed‐system conditions, with or without applying a fixed PH2 . Reaction products were characterized by Raman and FT‐IR spectrometry. Results indicate that decarboxylation reactions did take place, at variable degrees of progress, and that measurable excess CH4 was produced in one experiment using acetic acid. This suggests that methane may be produced from dissolved organic acids in natural aqueous inclusions in specific situations, possibly inducing errors in the thermodynamic interpretation. Abstract : Organic acids derived from petroleum fluids and dissolved in formation water might suffer decarboxylation upon postentrapment heating within the aqueous inclusion chamber, thereby generating excess CH4 in the inclusions. Fused silica capillary capsules (FSCCs), mimicking aqueous inclusions, were filled with acetic or formic acid solution and heated to 250°C in closed‐system conditions. Thermal decarboxylation of acetic acid producing CH4 (and CO2 ) in the FSCC is observed, which confirms the possible enrichment in CH4 in aqueous inclusions after entrapment.