Feasibility Study On Enhancing Oil Recovery By Chemical Assisted Thermal Recovery In Bohai Oilfield

The exploitation of heavy oil is always the focus of research, at present a lot of heavy oil reservoir in China has entered the last stage of development, the formation of natural energy shortage, resulting in heavy oil recovery decline, rising production costs, economic benefits plummeted, with the further deepening of the development process, the development becomes more and more difficult. At present, the exploitation of heavy oil reservoir by conventional techniques is the thermal recovery by steam injection, but the density and viscosity of vapor were lower, it is prone to gravity override and gas channeling, resulting in uneven vertical sweep efficiency of oil, and then lead to high residual oil saturation in the formation, steam sweep coefficient, oil displacement efficiency and recovery rate is reduced. Conventional techniques only temporarily reduce the viscosity of heavy oil, when the heavy oil leave the formation, with the decrease of the environment temperature and the decrease of formation temperature in the later stage, resulting in heavy oil temperature decreases. When the temperature is below the inflection point temperature of heavy oil, heavy oil viscosity quickly restored, resulting in the increase of seepage resistance and the rapid increase of water content. seriously affect the late shaft lifting and gathering and transportation technology. Present study mixed with hot fluids delivery process, but the drop of viscosity effect is limited, and then heating, adding adhesive and high pressure injection water, lead to the cost greatly increased, the exploitation effect and economic benefit of heavy oil are seriously affected. Therefore, it is necessary to study the effective thermal recovery technology, so as to further enhance the recovery of heavy oil.The contents of this paper is from the research on feasibility of improving oil recovery of chemical auxiliary heat recovery in Bohai Oilfield, the main purpose is to provide the feasible mining plan for offshore heavy oil development in the later stage, according to the specific circumstances of LD 27-2 oilfield, we carried out a series of work, as follows:Firstly we investigated some research of the thermal recovery of heavy oil has done, familiar with the heavy oil thermal recovery of theoretical knowledge and its development status, through analysis on current situation of heavy oil thermal recovery, it can be seen that the results of most studies chemical auxiliary heat recovery is in steam flooding or steam huff and puff in the process of adding surface active agent or foam, can effectively increase the steam sweep range, improves the efficiency of oil displacement, for improving the recovery rate of some help. But there are also some problems, and not all of the regions can be the development of chemical assisted thermal recovery, different regions of different reservoirs to carry out specific analysis.Secondly, we analysis the heavy oil thermal recovery main mining way of mechanism analysis, it is mainly aimed at the production mechanism and the application of steam injection and steam flooding to improve oil recovery, and point out their shortcomings, giving effective recommendations, at the same time, the influence factors of the thermal recovery of heavy oil are discussed. The main factors are the viscosity of heavy oil, the clay minerals of the formation and the sand production.Thirdly, according to the oil field geology and fluid properties combined with chemical agents designed part of the experiment, mainly for the interfacial tension between crude oil and chemical agents, when the interfacial tension is greater than the 10-2mN/m level, with the reduction of interfacial tension, the recovery rate gradually increased. Then, we carry out laboratory core flooding physical simulation experiments, studied the effects of different injection methods on recovery, the effects of different permeability formations for recovery, the effect of chemical agent concentration on the recovery, the effects of different chemical agents on recovery and the study on the chemical agent sweep coefficient. The results are as follows:(1) the chemical agent used in the experiment with Luda oil interfacial tension is 10"’-10"2mN/m, when the interfacial tension is greater than the 102mN/m level, with the reduction of interfacial tension, the recovery rate gradually increased. (2) the heavy oil ultimate recovery of chemically assisted thermal recovery is higher than simply steam flooding nearly 10 percentage points, for different permeability sand filled tube, the final recovery rate of the high permeability sand filled tube is higher than that of the low permeability sand filling pipe, but the stability pressure is too large. (3) In the same case of chemical agents, a large concentration of chemical agents for enhanced oil recovery is good, but after the chemical concentration halved the injection pressure is relatively low, in the case of little effect on oil recovery, it is appropriate to consider an experiment with a smaller injection pressure. (4) In permeability for the formation of 1000mD, using different reagents to first chemical injection then the injection of steam flooding for oil displacement, oil recovery are higher than pure steam drive, among them, the oil recovery efficiency of the whole drug is the highest. Screened out of the chemical agent in the follow-up 2000mD and 4000mD sand filled tube experiment, achieved good results, oil recovery rate is very high. (5) By filling sand tube parallel research chemicals sweep efficiency it was found that the chemical agents used in the experiments in different permeability formations can temporarily block the formation permeability, ensure the low permeability formations to product oil, thereby improving the overall oil recovery.By studying the above aspects, recognizing that conventional steam flooding of heavy oil EOR, the effect is not particularly obvious now, while the use of chemically assisted steam flooding can effectively improve the ultimate recovery of heavy oil, in the practical application, the oil field should be evaluated according to the actual situation to select the best plan for production.