Research On Improved Recovery Technique At The Late Multicyclic Steam Stimulation Stage In Extra Heavy Oil Reservoirs

Multicyclic steam stimulation in extra heavy oil reservoirs has been at the mid-late development stage, cyclic times of steam stimulation in oil wells is higher, and eight cycles of steam stimulation are performed in many wells, and even twelve or thirteen cycles are reached in some wells. Many problems appeared, such as high water cut ascending greatly, low oil yields in single well, low oil/gas ratio in cycle and low total degree of reserve recovery. Two plans were determined to solve the severe situation with which problems were faced in the late development stage such as reservoir pressure declining greatly and ineffective steam channeling in high permeability zones, etc. One is profile control of steam by foam fluid, temperature-tolerant foam was studied, and oil recovery might be enhanced by increase of steam sweep efficiency through plugging high pervious bed and overlap of steam coursed by low density and low viscosity was overcome. The second plan tried to find a new compound foam fluid which could control mobility of displacement agent, flush oil and reduce oil viscosity at the same time, then low-temperature steam or just hot water could be used to displace viscous oil and the oil recovery could be increased also. Based on exploitation status of heavy oil reservoirs, affecting factors on recovery effect at the late stage of multicyclic steam stimulation in heavy oil reservoirs are analyzed by compositive ways, such as modern reservoir engineering, oil field exploitation performance and monitoring data, and reservoir simulator, etc., in combined with steam stimulation exploitation experience in Shanjiasi heavy oil reservoir of Binnan Oil Production Plant, and research on remainder oil distribution characteristics at the late development stage of multicyclic steam stimulation."Oil displacement and profile control"compound oil displacement system is developed on the basis of research on combination synergetic effect between among kinds of surfactant and chemicals, and optimization of foaminess and interfacial activity of surfactants. And, compound oil displacement system is optimized further, finally"plugging and profile controlling, oil displacement and visbreaking"high-temperature-tolerant oil displacement system is developed. Formation and transmission mechanism of foam flow in porous media are studied in the paper, and mechanism of plugging and profile controlling of foam were also determined. Effect of temperature, salinity, pressure and alkalinity on foam stability were examined, and effect of inject program and inject parameters were investigated by laboratory imitate oil-displace experiment, then optimum inject program was defined. For Shanjiasi heavy oil reservoir, three-dimensional distribution is ascertained by reservoir simulator, and research on Intermission steam flood technique and its matching technics are performed, and oil displacement projects, such as gas injection interval, best pattern well spacing and injection/production parameters, etc., are optimized, and thermal recovery reservoir management pattern, like injection/production strategy, is researched by foundation of heat flow and physical flow model. Field test of flooding-control by foam were in progress in Gudao and Binnan oil produced factory. Obvious increase of inject pressure of steam might be evidence of foam block of high pervious bed, and abrupt increment of oil yield per day showed the expected function of flooding control became true. And high daily oil yield sustained for a long time. The poor situation of the test wells was changed thoroughly after the field test. The result of laboratory and field test all showed that foam flow could be used as a efficient displacement agent, and might be used widely to enhance oil recovery, even in high produced water content oil field.