Chemical-Reaction Mechanisms That Govern Oxidation Rates During In-Situ Combustion and High-Pressure Air Injection

Abstract

Summary The lack of an accurate reaction model for petroleum-oxidation rates is a serious hindrance to the simulation of oil-recovery processes that involve air injection. However, the chemical literature on hydrocarbon oxidation contains many examples of possible reaction mechanisms that could serve as guides. These mechanisms were screened to identify generally accepted reaction paths that could help reveal how oxidation occurs in petroleum reservoirs. It was found that there are at least eight groups of fundamental reactions that can seriously affect oxidation rates of crude oils or their pyrolysis products. These eight reactions are as follows: two that lead to hydroperoxide formation; “branching” by hydroperoxides; two reactions governing the negative temperature coefficient (NTC) region; oxidation inhibition; at least one rate-controlling reaction at very high temperatures; and the combustion of coke that is produced by pyrolysis. Each of these groups exerts an influence within a separate, identifiable range of conditions. These reactions, and the conditions under which they become important, are outlined in this paper. Various oxidation behaviors that were reported for both light and heavy crude oils were then compared and aligned with the eight identified reactions. The result was a framework for selecting pseudoreactions that can facilitate the prediction of the oxidation kinetics under a wide range of oilfield conditions. Some of these pseudoreactions involve the direct representation of free radicals or other chemical intermediates, which is a departure from conventional practice for in-situ-combustion simulation. The new reaction framework is expected to serve as a reliable guide to the construction of predictive reaction models and, consequently, improved simulation of both in-situ-combustion and high-pressure-air-injection (HPAI) processes.

Integrative Investigation of Low-Temperature Oxidation Characteristics and Mechanisms of Heavy Crude Oil

“…As reported by many peers, the LTO stage mainly contains two types of reactions: oxygen addition reactions to generate hydroperoxides and isomerization and decomposition reactions of hydroperoxides to generate oxidized compounds (ketones, alcohols, aldehydes, etc. ), CO 2 , CO, and H 2 O. ,,,, Table lists the produced gas compositions measured by GC at varying oxidation temperatures. It could be seen that only a small amount of oxygen was consumed at temperatures below 80 °C, elucidating that the oxygen addition reactions were extremely weak.…”

“…To date, an in situ combustion (ISC) technique has been considered as a potentially efficient enhanced oil recovery (EOR) method. − An ISC process is commonly divided into three dominating stages, namely, low-temperature oxidation (LTO), fuel deposition (FD) and high-temperature oxidation (HTO). ,− Among these stages, LTO has been proven to be extremely complicated due to many different kinds of complex oxidation reactions occurring simultaneously in this stage. The temperature must pass through the LTO interval at the early ignition period of an ISC process; the LTO residues (oxidized fractions and their condensation mixtures) have key impacts on the formation of coke that directly determine the advance and sustainability of the combustion front .…”

Influence of Carbonate Minerals on Heavy Oil Oxidation Behavior and Kinetics by TG-FTIR

“…The thermal behavior of the two heavy crude oils with different physical-chemical properties characterized by TG is presented in Figure 2. Three main stages were iden-tified as LTO, FD, and HTO from low to high temperature, respectively [6,27,33,34]. In addition, oil-1 also exhibits a distinct mass loss peak in DTG curves at approximately 100 • C. This is the evaporation of water contained in the heavy oil, which can be supported by the water peak appearing in the FT-IR spectra of effluent gases (Figure 3).…”

“…Energies 2021, 14, x FOR PEER REVIEW 5 of 13 (distillation process) plays a vital role in the oil displacement mechanism in the ISC process. The main reaction that occurs in LTO is the formation of hydroperoxides by oxygen addition reactions (Reaction (R1)) and their subsequent isomerization/decomposition reactions (also described as bond scission reactions) [30,33].…”

Exothermal Property and Kinetics Analysis of Oxidized Coke and Pyrolyzed Coke from Fengcheng Extra-Heavy Oil

“…In addition, China’s heavy oil resources are dominated by the northwest and Liaohe oilfield, representing more than 60% of the nation’s total oil. Due to the decreasing oil production of conventional and mature reservoirs coupled with the rapid increase in global energy demand in recent years, heavy oils have become an increasingly significant energy resource. − As an effective and potential thermal recovery method for heavy crude oil, in situ combustion (ISC) technology has been increasingly studied. , During the dynamic ISC process, a series of continuous and complex reactions, such as distillation volatilization, low-temperature oxidation (LTO), fuel deposition (FD), and high-temperature combustion (HTC), are generally believed to occur. − Oxygen addition reactions of some active aliphatic compounds are regarded as the main LTO reaction pathways that produce LTO derivatives. , Then, the coke precursors can further generate coke in the FD stage. − The available heat is released by coke combustion, which can promote the in situ cracking and upgrading of heavy oil. , These newly produced light fractions can be distilled into the gas phase and further migrate and condense. , Additionally, the injected gas results in increasing the reservoir pressure and enhancing crude oil recovery. , …”