A Study On Aquathermolysis Kinetics Of Heavy Oil And Its Application

With the increase of the global economy, the oil and gas demanding is also increasing. The decrease in the exploitation and production of the conventional oil indicates that the exploration of heavy oil becomes crucial in the nation's energy strategy. The remarkable characteristic of heavy oil reservoir is that the oil has high viscosity, high density and low mobility. This characteristic makes it difficult to produce the heavy oil economically efficient using conventional techniques. The primer production method currently using in the industry is steam injection. The effect steam injection is reinforced by a mechanism called aquathermolysis, which is a reaction happened between steam and heavy oil at high temperature in the subsurface porous media. This mechanism improves the quality of heavy oil in-situ, and decrease the viscosity of the heavy oil permanently. The production of the heavy oil using the mechanism of aquathermolysis reaction is a latest technique and it has a broad future so far. Hardly any paper is published on the study of aquathermolysis of heavy oil mechanism. Therefore, the mechanism and kinetics of aquathermolysis reaction are intensely studied in this paper. The study was accomplished using methods of theoretic analysis, laboratory experiment and numerical computation. The study results were applied to heavy oil production in the industry. The production results indicate that the oil recovery was improved and the quality of heavy oil was improved dramatically. The Main contents and innovations of this study include the following: (1) The mechanism of aquathermolysis reaction during steam injection process The transforms of heavy oil during heat-degradation include collateral reactions of cracking and polymerization. In heavy oil's structure, the bridge-bonds that consisted of heteroatoms are weak; thus these bonds are easily to be broken under steam injection condition. This break of bridge-bonds can stimulate a series of favorable reactions, which is very important in aquathermolysis reaction. The active hydrogen induced by aquathermolysis reaction can capture free structure and hydrocarbon fragment, which helps to prevent the interlinkage of reactant chain. As a result, the viscosity of the heavy oil is irreversibly reduced. The aquathermolysis reaction follows the acid-alkali catalysis route when high temperature steams present. The present of formation mineral and metal ions can also catalyze the reaction. (2) Equilibrium compositions of model compounds for the aquathermolysis reaction of heavy oil Thiophene and tetrahydrothiophene were used as model compounds for the aquathermolysis reaction of heavy oil. Based on the equilibrium composition calculation, the effects of temperature, pressure and feed ratio on equilibrium were analyzed. The results show that the reaction lacks water when the ratio of water/tetrahydrothiophene is less than 3 and that of water/thiophene is less than 4. In addition, high temperature and low-pressure conditions during aquathermolysis reactions help to produce plenty of gaseous products. However, these conditions are unfavorable in desulfurization of the oil. The results also show that the water is enough for the reaction when the ratio of water/tetrahydrothiophene is more than 3 and that of water/thiophene is more than 4. For these ratios, the equilibrium reaction is affected slightly by the temperature, pressure and feed ratio. (3) The effects of reaction conditions on aquathermolysis reaction of heavy oil Base on the results of indoor experiments, the effects of reaction conditions (temperature and time) on the quality of heavy oil are analyzed with and without the presence of the formation mineral and the catalyst. The effect objects include viscosity, molecular weight, gas yield, the distribution of hydrocarbon and four compositions. The results indicate that viscosity and molecular weight of heavy oil decrease with time and the increasing of temperature. Meanwhile, heavy oil is significantly lightened. Besides, the presences of mineral and metal ions catalyze the aquathermolysis reaction and improve the quality of heavy oil; different minerals have different catalysis effects. (4) The transform rule and quantitative calculation of mineral The transform rule of mineral during steam injection is summed up. The contents of mineral change in plane with temperature nearly. A quantitative method of calculating the amount of mineral varieties is developed on the basis of quality action and conversation law using the injected and produced water data. (5) The development of two different lumping kinetic models for the aquathermolysis reaction of heavy oil to the different existent conditions of mineral. Two different lump kinetic models are developed for the aquathermolysis reaction of heavy oil with and without mineral present. When the formation mineral is absent, it is appropriate to employ the four-lump model of gas, C5-C15, C16-C30 and C31+. On the other hand, when the formation mineral is present, it is better to employ the five-lump model of gas, saturate, aromatic, resin and asphaltene. (6) The calculation of parameters in kinetics models using a direct method and the establishment of the model. A direct method was developed by combine the methods of Runge-Kutta, Monte-Carlo and complex method. This method was used to calculate the parameters in kinetic models. The calculation results show that that the presence of the formation mineral and metal ions reduces the active energies in the cracking of heavy compositions. This energy reduction helps to produce more light oil component products aquathermolysis reaction. Moreover, the experimental data and the model prediction are consistent. This suggests that the lump model explains well the reaction mechanism of aquathermolysis of heavy oils at the absence of formation minerals. (7) Practical applications of laboratory research for oil recovery in Liaohe Oil Field. The research results were applied to seven heavy oil wells in different districts of Liaohe oil field from 2003 to 2004. The production history showed that the cumulative oil recovered during the production period increased 2661.8 tons; on average, each well increases oil recovery of 380.3 tons. The ratio of cost to benefit is 1:3.6. It was observed that the viscosities of heavy oils reduced dramatically after recovered. In recovered heavy oil, the amount of saturate and aromatic components increased; meanwhile, the amount of resin and asphaltene components decreased. This indicates that our improvement in aquathermolysis reactions significantly enhances the qualities and reduces the viscosity of heavy oils. Furthermore, the improvement in aquathermolysis reactions reservoir facilitate the recovery of heavy oil reservoir economically more efficient.