Semi-Open System Simulation of Organic-Rich Shale To Produce Organic Acids

Abstract

The deeply buried organic-rich black shale in basins generates a considerable amount of organic acids during thermal evolution, which is of great significance for the modification of the reservoir pore structure and the evaluation of hydrocarbon product mobility. However, research on the types of organic acids generated is still insufficient, leading to a significant underestimation of organic acid yields. In view of this, this study utilized a semi-open pyrolysis simulation device to simulate different maturity stages of organic-rich black shales through pyrolysis experiments. High-performance liquid chromatography (HPLC) was used to analyze the composition of water-soluble organic acids in the products. The results showed that the yield of organic acids was highest in the early stage of organic matter thermal maturity, reaching up to 8.58 mg/g of total organic carbon (TOC), and was rich in a variety of organic acids, mainly including quinic acid, formic acid, acetic acid, propionic acid, n-butyric acid, oxalic acid, lactic acid, malic acid, and tartaric acid. As thermal evolution progressed and hydrocarbons were generated in large quantities, the acid yield rapidly decreased, reaching 0.11 mg/g of TOC. Therefore, the transformative effects of acidic fluids formed by kerogen in source rocks on sandstone reservoirs can be traced back to the period before oil and gas migration. Additionally, the diversity of organic acid types has been significantly underestimated in most studies.