Study On The Law Of Heavy Oil Viscosity Reduction By CO₂ And Viscosity Reducer

With the dramatic increase in oil consumption of the world, the conventional petroleum reserves are dwindling. In order to ease the intensive energy supply, heavy oil was occupied by an increasing proportion in oil exploitation and production. Generally, heavy oil have good mobility in reservoirs, but the change of conditions such as temperature, pressure and the influence of overcoming gravity and friction in process of wellbore flowing, leading to increment of oil viscosity and resulting in unsuccessful lifting of oil to the ground. Therefore it’s really important to reduce viscosity of oil and to understand the flow pattern of liquid in wellbores.First of all, the chemical viscosity-reducing experiments were studied in the paper. On the basis of laboratory experiments, two viscosity reducers were successfully screened out, they respectively are water-soluble viscosity reducer HEOR-5 and oil-soluble viscosity reducer YR5. At the same time, factors which affect viscosity reducing effect were taken into account, such as concentration of viscosity reducer, temperature and water cut of heavy oil. As a result, the water-soluble viscosity reducer HEOR-5 have a good compatibility with formation water, under the condition of 50 centigrade, oil/water ratio of 7:3 and concentration of 1.0%, HEOR-5 work very well and the visbreaking rate is as high as 94.1%. The visbreaking rate of oil-soluble viscosity reducer YR5 is 92.6% under the condition of 50 centigrade, concentration of 1.0% and water cut of 50%.Secondly, solubility of CO₂ in heavy oil or emulsion with different water cut, swelling factor, density and viscosity of heavy oil dissolved CO₂ was researched by laborayory experiments. The results show that solubility of CO₂ increases with increment of pressure in Zhangwu heavy oil. The swelling factor of heavy oil linearly increase with increment of solubility of CO₂, but the change of density and viscosity of saturated oil is opposite to swelling factor, oil viscosity descreases with increment of solubility of CO₂. At the same CO₂ solubility, the higher of water cut of heavy oil, the smaller addition of swelling factor, the lower of viscosity. When the water cut less than 30%, density of oil decreases, and when the water cut more than 30%, oil density increases. The 30% water cut is the cut-off point of density.The result of compounded effect of oil-soluble viscosity reducer YR5 and CO₂ is better than the separate effcct. The effect of dissolution, dispersion, adsorption and demulsification of YR5 and the effect of swellbility, viscosity reduction of CO₂ are complementary, greatly improved the mobility of heavy oil. There are many ways to use CO₂ to enhance oil recovery. A model of the distribution of temperature and pressure along the wellbore for a mixed system of heavy oil, carbon dioxide and viscosity reducer is established. The model assumes that the temperature of the reservoir can restore after the injection of carbon dioxide and viscosity reducer. The temperature, pressure and viscosity of the mixed system along the depth of wellbore are calculated by compiled calculation program.