Study On The Formation Mechanism Of H₂S By Aquathermolysis Of Heavy Oil

With the depletion of conventional oil,the exploitation and utilization of heavy oil has received more and more attention.However,heavy oil has the characteristics of high density,high viscosity and difficult to be mined.Steam injection thermal recovery is an effective min-ing method.When high temperature and high pressure steam is injected into the oil layer,complex chemical reactions will occur to generate a large amount of hydrogen sulfide(H₂S)gas.H₂S is a corrosive and toxic gas,which brings great safety hazards to field workers and equipment.So,aiming at the phenomenon of hydrogen sulfide(H₂S)generated during steam injection in the reservoir,this paper takes the heavy oil of Liaohe Du 84 block as the research object,and explores the mechanism of H₂S generated by aquathermolysis through thermal simulation experiments.The results have important guiding significance for the formation and prevention of heavy oil thermal recovery H₂S.The properties of the reactants were investigated,and the characteristics of aquathermol-ysis reaction in the development of heavy oil steam injection were analyzed in combination with on-site heavy oil samples to lay a theoretical foundation for scientific prediction of H₂S production and control of H₂S corrosion and hazards in sulfur-containing oil fields.This paper first uses four-component(SARA)analysis,elemental analysis(C,H,N,S,etc.),viscosity-temperature relationship,and Fourier transform infrared(FTIR)analysis of crude oil and SARA.The results show that the heavy oil in the Liaohe Du 84 area is a low sulfur and super heavy oil.The content of saturated fraction and colloid is higher,but the content of colloid and aromatic S is higher;heavy oil contains long aliphatic chain and fused ring carboxylic ac-id or aldehyde and ketone,and benzene ring is less.Aquathermolysis is accompanied by the generation of thermal cracking reaction.It is clear that the mechanism of thermal cracking to form H₂S provides a basis and comparison for understanding the mechanism of H₂S formation by aquathermolysis.The thermal cracking experiment of heavy oil was carried out.The effects of time and temperature on thermal cracking were investigated.The influence of thermal cracking time and temperature on gas products and SARA and the reaction path were obtained.The thermal cracking time and tem-perature are directly proportional to the amount of H₂S produced.Increasing the temperature is beneficial to the upgrading of heavy oil.The thermal cracking of heavy oil is mainly CH₄,C₂H₄,C₂H₆,C₄+,CO₂.,H₂ and H₂S.In the thermal cracking process,free radicals are first generated.On the one hand,the free radicals form a small molecular structure on the one hand;on the other hand,the free radicals attack the sulfur bridge and the aromatic compound and cause dealkylation and hydrocracking.Through the aquathermolysis experiment of heavy oil,the effects of different water-oil ratio,reaction temperature,reaction time,superheat and supercooling on the formation of H₂S and the formation mechanism were investigated.The results show that the aquathermolysis reaction products mainly include organic gases such as CH₄ and C₂H₆ and inorganic gases such as CO₂,H₂ and H₂S.The reaction time,temperature and superheat are positively corre-lated with the amount of H₂S,and the degree of subcooling and H₂S production.It is nega-tively correlated;when the water-oil ratio is 2,the aquathermolysis reaction is the deepest,and the amount of H₂S is the largest.SARA analysis shows that the presence of water is bene-ficial to the upgrading of heavy oil,that is,the increase of saturated hydrocarbons and aro-matic hydrocarbons,and the reduction of colloid and asphaltenes.The difference is that as the degree of superheat increases,asphaltenes show an increasing trend.The oil after the reaction in the superheated/cold state was analyzed by X-ray photoelectron spectroscopy(XPS).The results showed that the sulfur compounds in the heavy oil were mainly thiophene,sulfoxide and sulfone.The nitrogen-containing compounds are mainly pyridine,pyrrole and quaternary amino groups;in the superheated state,the carboxyl group is cleaved by a C-O bond to form a carbonyl group,and the carbonyl group generates a large amount of CO₂.The H₂S generation source is different under different water vapor conditions.H₂S is mainly produced by sulfide,sulfone and sulfate in the superheated state;H₂S is mainly produced by sulfone,sulfoxide and sulfate in the supercooled state.Finally,the kinetic model of H₂S formation by thermal cracking and aquathermolysis of heavy oil was established by kinetic experiments.The apparent activation energy of H₂S gen-erated by thermal cracking of heavy oil was 68.59 k J/mol.The apparent activation energy of H₂S produced by aquathermolysis of heavy oil is 45.13k J/mol.By comparing the apparent ac-tivation energy of heavy oil thermal cracking and aquathermolysis,thermal cracking is not dominant in 200?300?.