Study On Catalytic Aquathermolysis Of Heavy Oil At Relatively Low Temperature

With increasing demands for energy resources and serious shortage of conventional petroleum, heavy oil, whose reserves share 70% of the total quantity of petroleum in the world, has attracted worldwide interest. However, its high viscosity often causes difficulties in exploitation. Refer to principle of upgrading of petroleum, catalytic aquathermolysis recovery developed in 1980s is a new exploitation technology with great potential for heavy oil, especially for extra heavy oil. In this technology, chemicals, as catalytic viscosity reducers CVRs, are adding into the oil layer to reduce the viscosity, decomposing the asphaltenes and resins permanently.Hence, a number of scientists conducted a lot of researches in which various catalysts were added to catalyze the aquathermolysis. Currently, the catalysts used in this technology were mostly transitional metal ion salts, transitional metallic compounds and some acid or base catalysts. Meanwhile, they study the mechanism of viscosity reduction through catalytic aquathermolysis and pointed out the hydrodesulfurization is the main reason for viscosity reduction during this process, the adding CVRs catalyzed the breakdown of C-Ss. Parts of them also conducted the field tests and obtained good effects to some extent. Their study promotes the development on this techonology and provides the research direction and thinking for the further study.The CVRs in above study can maxmum their catalysis at above 240℃, and the temperature in oil floor after steam injection gradually lower with the increasing depth of the oil floor and is difficult to remain above 240℃, so there is no enough energy supplied for catalysis. Inaddition, the theory of "breakdown of C-S" can describe the mechanism of viscosity reduction through catalytic aquathermolysis at above 240℃, but not explain that at relatively low temperature. These years, we studied the catalytic aquathermolysis at relatively low temperature and gained the great achievement both in laboratory and oilfield. This paper presents the study on synthesis of CVRs, laboratorial catalytic aquathermolysis experiments, mechanism and kinetics of viscosity reduction of heavy oil, and field texts.We proposed synthesis thinking of a type of CVRs with effective catalytic center modified using organic ligands, and synthesized four kinds of CVRs. Later, we conducted the catalytic aquathermolysis at the whole temperature range 40-280℃, and analyzed the influence of reaction time to the viscosity reduction. The results showed that when the reaction temperature is below the 140℃, there is no catalysis, the real viscosity reduction is below 10%, and little content of heavy composition is decreasing; when the reaction temperature is between the 140℃and 200℃, the rate of viscosity reduction largely increase and the content of heavy components sharply decrease along the increase of the reaction temperature, the catalytic aquathermolysis mainly happens at this temperature range and the real viscosity reduction at 200℃is above 90%; when the reaction temperature is between the 200℃and 280℃, the rate of viscosity reduction and the content of heavy components maintain constant along the increase of the reaction temperature, the viscosity reduction can keep above 95% at this temperature range. In the whole process, the viscosity reduction can finished at 24 h.Then, we separated the four compound groups, namely, asphaltenes, resins, saturated and aromatic hydrocarbons from heavy oil before and after catalytic aquathermolysis through the column chromatography-based SARA method, and further isolated the oxygen and nitrogen containing compounds in resins, extracted and collected the organic compounds in reaction waters and gases after catalytic aquathermolysis. We used thin-layer chromatography-flame ionization detection (TLC-FID), element analysis (EL), nuclear magnetic resonance (NMR) and gas chromatography/mass spectroscopy (GC/MS) to comprehensively analyze the changes of heavy oil, reaction water and pyrolytic gas during catalytic aquathermolysis. The results show that there are three types of action during catalytic aquathermolysis:desorption, depolymerization and pyrolysis, and the desorption and depolymerization are the mainly reactions. These two types of actions are caused by the disruption of the associating structure due to the relatively weak actions, such as van der Waals forces and hydrogen, ionic and coordinate bonds, which play the leading role in high viscosity of heavy oil. Therefore, reducing the viscosity of heavy oil to a large degree permanently in oil layer is feasible, only through disrupting the relatively weak actions at relatively low temperature, needing not break the strong chemical ones at very high temperature.Meanwhile, we analyzed the change law of the organic compounds in saturated and aromatic hydrocarbons, reaction water and gas following with the changes of reaction time and temperature, and deduced the kinetic formula. It is found that when the reaction temperature is below the 140℃, few or no chemical actions happen; When the reaction temperature is between the 140℃and 160℃, there is only desorption exited during the reaction; When the reaction temperature is between the 160℃and T (depolymerization), the desorption and depolymerization cause the decrease of heavy compositions. The T (depolymerization) is above 180℃and below 200℃; when the reaction temperature is between T (depolymerization) and 280℃, three types of actions such as desorption, depolymerization and pyrolysis exit during the reaction. Following with increase of the reaction temperature, the reaction velocity increases in the whole process, but the reaction balance transfers only at the temperature below T (depolymerization), and keeps constant when the temperature is between T (depolymerization) and 280℃. Especially, at 200℃, desorption, depolymerization and pyrolysis finish at 12,18 and 24 h, respectively.At last, we conducted the field tests in Henan oilfield and obtained good effects. The viscosity reduction reached to 80%, and the production increased by 200 t in a period after using catalytic aquathermolysis recovery.To sum up, we proposed synthesis thinking of a type of CVRs with effective catalytic center modified using organic ligands, studying the synthesis of CVRs, mechanism and kinetics of catalytic aquathermolysis and field tests. Therefore, it is very important to investigate the cost catalytic center and organic ligands. The mechanism and kinetics of viscosity reduction of real heavy oil through catalytic aquathermolysis demonstrate the feasibility of large viscosity reduction of heavy oil irreversibly at oil layers. The conslusion can provide the research direction and theory instruction for thoroughly solving the contraction that the oil layers can not provide enough energy for viscosity reduction through catalytic aquathermolysis. Developing good CVRs will improve the catalytic aquathermolysis recovery to greatly enhance the recovery of heavy oil. This technology has widely prospects and its industrialized application will achieve in the near future, and eventually, the exploitation of heavy oil will not the world difficult problem puzzling us.The innovative points of this paper are research thinking, methods and conclusion. Firstly, we sythensized of the multi-function CVRs with good universality, which can show good effects at relatively low temperature (180-200℃), and meanwhile improve some disadvantages in recovery process to enlarge the impact scope and promote the oil displacement efficiency. Few of this research thinking are reported in provious study. Secondly, we firstly analyzed the changes of organic compounds in heavy oil, reaction water and gas comprehensively. Finally, we firstly describe the mechanism of viscosity reduction through catalytic aquathermolysis at relatively low temperature, and clearly stated the leading reason of high viscosity of heavy oil. Our low temperature theory "the weak chemical reaction is leading role" replenishes the high temperature theory "breakdown of C-S", extends the mechanism to a lower temperature, to a wider range. The conclusion indicates that reducing the viscosity of heavy oil to a large degree irreversibly at oil layers is feasible, and enhancing oil recovery largely through catalytic aquathermolysis at oil layer is possible. Meanwhile, it can provide the new thinking and theory instruction for sythensizing the catalytic viscosity reducer.