| Steam flooding is the most prevalent method so far for enhancing heavy oil recovery, which also has some deficiency. First, overriding of steam makes sweep efficiency low when the thickness of layer increases. Secondly, finger advance is serious during steam flooding, especially in anisotropic layer where the injected steam often crossflows through high permeability zone, resulting in more heat loss and lower sweep efficiency. Thirdly, a reduction in oil production and an increase in steam/oil ratio can be observed at the later stage of steamflooding, which means that a large amout of heat will be left in rocks and fluids and wasted if steam is continuely injected. It is important to conduct studies on mechanism of technologies for improving steam flooding efficiency.Based on the practical production situation of Block Qi40 in Liaohe mid-depth heavy oilfield, the development efficiency of steam flooding in pilot test area, enlarged test area and extended were evaluated in the paper, respectively, proposing the main problems. Production data showed that steam flooding applied successfully in Block Qi40, however, a lot of problems exposed in this process have been in need of proposal. These problems included that the 4 well groups in pilot test had been in the period of later stage of steam flooding and that the situation of more investment and less production was so serious that it should be coverted to other development methods. And steam breakthrough control techniques should be studied in that the breakthrough happened in a percentage of 45% of 7 well groups in enlarged test area causing many problems in the process of production. Oil production also declined in the extended test area because of unequal employment of reservoir, poor effects of laying injection, and breakthrough, which demenstrated new techniques should be studied to improve development effect of steam flooding.On the basis of main problems in every well group, research on mechanism of new techniques for improving steamflooding efficiency is conducted in this paper.First, in order to control the breakthrough in the process of steam flooding, filtration theory of breakthrough was studied to determine the main factors of maintaining the stable displacement, including the effects of mobility ratio, locations of different interface and spacing between injecting and producing wells on the stability of displacement interface, which showed in theory that kickoff pressure gradient exerted an effect on displacement stability. On the other hand, in experiments 1-dimensional and 2-dimensional physical simulations were conducted and a new breakthrough control system, sodium humate, was developed which was characterized by easiness to be pumped, a good tolerance of salinity(NaCl concentration could be up to 40000mg/L and CaCl2 concentration up to 8000mg/L), and a good temperature tolerance(290℃). Experiment results showed that the system had a good impact on cores of various permeability, the plugging ratio could achieve 95% and it also could not plug low permeability strata but high permeability strata. The optimization of formula was determined to be sodium humate(concentration of 9%),aldehyde(concentration of 1.5%),resorcin(concentration of 2.0%), optmical pH value range (7-9).Secondly, a technique for controling fluid mobility of condensed water by adding chemical agent was discussed by means of fractional flow formula and Buckley-Leverett displacement theory. And a new method, using RRF(residual resistance factor) to demenstrate the change of mobility ratio with and without adding chemical agents, was proposed to simplify the calculation load in the experiment. MA was screened to carry out the oil displacement experiments and the results showed that RRFw increased as temperature and injection amount went up. On purpose of maintaining the displacement efficiency, the temperature should be as high as 220℃or more and injection amount should not be lower than 1PV. Water relative permeability was reversible with the temperature declining. The fact that RRFo approached to be 1 with or without MA injection showed MA plugged not oil but water. Oil displacement results showed that displacement efficiency was 49.9% after injecting saturated solution of MA when temperature decreased from 200℃to 160℃, which was 10.1% higher than pure hot water flooding at 200℃and 11.7% higher than that of 160℃. When temperature lowered to be 60℃,37.1% of displacement efficiency could be attained which was less than 200℃pure hot water flooding and more than 60℃.Thirdly, mechanism of converting from steamflooding to hot water flooding was disscused. Experiments were carried out in which 3 programs, were designed to be continuous steamflooding, converting to hot water flooding and gas-water alternating injection. And the displacement efficiency was 4.42%,2.99% and 3.76%, respectively, which showed that hot water flooding was the best choice for a post steamflooding project because of its low costs. According to monitoring data of static and dynamic which is fitting well to the results of numerical simulation, microseismic test and new well test, the resident oil distribution in internal layer and interlayer was calculated and analyzed after steam flooding. And steam absorption in oil layers without testing data is determined by formula. The results showe that remaining oil in place in pilot test area is determined to be 38.3×104t and oil saturation to be 33%. The designing optimazation of petroleum for converting steam flooding to hot water flooding in pilot test area is also conducted in this paper. The parameters are optimized in numerical simulation to be 150℃of injecting temperature in down hole (equal to 180 in well head),1.2:1 of rational injecting/producting ratio, 100t/d of rational water injection and commingled water injection as soon as possible, respectively.
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