Implementation of the methodology for the extraction of soluble organic matter in shale and calcarenite for the identification of organic compounds and biomarkers

Abstract

Within the parameters that affect the method of extraction of soluble organic matter in rocks, is the composition and volume of the solvent as well as the characteristics of the matrix, so in this research work the effect of using two mixtures of acetone-hexane and acetone-dichloromethane solvents, in three samples of shale and two of calcarenite, from the “El Álamo” Canyon of Viesca, Coahuila, for the identification of organic compounds preserved in the soluble fraction of the sedimentary organic matter (bitumen) recovered by implementing the Microwave Assisted Extraction (MAE) method. In the development of this extraction method, 3 g of sample were weighed in Teflon cups, adding 25 ml of solvent mixture acetone-hexane (1:1) and in another series 25 mL with acetone-dichloromethane (1:1), The vessels were placed in a CEM microwave oven, model MARS 5, with a power of 1200 w, ramp 10:00 min, PSI 100, temperature 110°C, extraction time 15 min and cooling time 15 min. The purpose of testing two mixtures of solvents (acetone-hexane and acetone-dichloromethane) is to determine with which mixture the greatest amount of soluble organic matter is obtained in order to subsequently proceed to the identification of organic compounds and biomarkers using Gas-Mass Chromatography. . In this research work it was shown that the solvent mixture in which the greatest amount of soluble organic matter was extracted was acetone-dichloromethane. Regarding the identification of linear alkanes and biomarkers, in the gas-mass chromatograms resulting from the characterization of the samples, they showed that the acetone-dichloromethane solvent mixture showed better identifications, regardless of the type of sedimentary rock. This mixture allowed the identification of long chain alkanes (n-C₄₄H₉₀); but this is not the case with short-chain alkanes below n-C₁₈H₃₈ due to the polarity of the solvent, or because the sample could present biodegradation or thermal alteration.