Research On The Technology Of Improving Steam Injection Efficiency For Heavy Oil Reservoir

As the important part of the petroleum energy,the development potential of heavy oil is more and more big; And steam huff and puff is the main way to develop heavy oil reservoir in China’s Current Stage; In the process of steam stimulation, steam injection efficiency directly affects the development effect of the reservoir; Therefore, combined with the practical condition of reservoir, this paper researches how to improve steam injection efficiency of heavy oil reservoir mainly from three aspects based on the analysis of heating effect in the reservoir during the process of steam injection:firstly, optimizing injection-production parameters in the actual process of heavy oil development by using numerical simulation technology; secondly, researching carbon dioxide-assisted steam stimulation technology in steam injection process of heavy oil reservoir to improve steam injection efficiency; thirdly, in accordance with the phenomenon of high steam injection pressure and steam can’t be injected, researching steam injection after fracturing technology to reduce steam injection pressure and improve development effect of steam injection.First of all, combined with Marx-Langenheim method and Faroup Ali method, this paper applies energy balance equations to calculate steam zone area, hot water area and total heating area in process of multicycle huff and puff for heavy oil reservoir; the way of Marx-Langenheim is mainly used for the reservoir with shale top and shale bottom, and the way of Faroup Ali is mainly used for the reservoir with shale top and sandstone bottom which is consisted with bottom-water reservoir.Through the calculation and analysis, the results show as follows:with the increase of steam injection days, steam zone area, hot water area and total heating area which heat oil layer increase linearly; with the increase of steam injection cycles, affected radius of steam gradually enlarges, total heating area of reservoir gradually increases, and the tendency gradually changes slow; Due to the influence of the reservoir depth, steam dryness is low in the bottom of the well as a result of the depth of actual reservoir is deep, most of the steam change into hot water, so the proportion of hot water is large and proportion of steam is smaller in total heating area. Based on the analysis of the heating area, temperature distribution of heating oil after steam huff and puff is researched by the way of Lauwerier; because of steam injection, the temperature near wellbore is high; the farther the distance from the wellbore, the lower the temperature of the reservoir, to a certain distance, the temperature fells sharply to reservoir temperature; Along with the increase of steam injection cycles, the distribution of temperature which is higher than the initial is more and more widely with the increase of heating area. After analysis on heat distribution of reservoir, Willman method is used to calculate heat loss of reservoir in the process of steam injection and Prats method is used to calculate the heat efficiency; Along with the increase of steam injection cycles, heat loss of reservoir increased and the heat efficiency reduced with the increase of heating area.After the analysis of heated effect to reservoir, based on the literature analysis, in order to improve steam injection effect for reservoir, the first consideration is that the injection-production parameters in the process of steam huff and puff for heavy oil development should be optimized. The paper optimizes parameters which affect heavy oil development by using numerical simulation method about thermal production. It mainly uses Petrel geological modeling software to build comparatively accurate single well model and reservoir geological model, and then combined with actual production dynamic model and rock flow model, it establishes CMG numerical simulation model for steam huff and puff; on the basis of reserves fitting and production fitting, it uses orthogonal experiment designning method to design twenty-five ways, and then uses stage cumulative oil production and oil-steam ratio as evaluation index, optimizes some injection-production parameters of well group, such as cyclic steam injection volume, steam injection rate,steam dryness, soaking days, producing rate. If the evaluation index is different, the corresponding optimization results are also not completely the same; for the parameters with different optimization results, it need to redesigne simulation schemes while keeping other parameters constant, and then gets the best solution by single factor analysis.On the basis of numerical simulation for steam injection parameters optimization, we can use existing numerical simulation model which is suitable for the real reservoir to research carbon dioxide-assisted steam stimulation technology how to improve development effect, the research for injection scheme of carbon dioxide is mainly from three aspects:One is the most suitable time, another is the better injection pattern, the third is the reasonable carbon dioxide injection volume. Based on the simulation results, for actual steam stimulation of heavy oil reservoir, the best time of carbon dioxide injection is the same time as steam injection, the better injection pattern is straight injection with steam, and at the moment of the gas to liquid ratio around0.4, the carbon dioxide injection volume is reasonable.In accordance with the phenomenon of high steam injection pressure and steam can’t be injected, the paper deeply researches another auxiliary steam injection technology of heavy oil, fracturing. The main research is about the relationship between wellhead pressure and steam injection rate, steam injection days, soak days; it comparatively analyzes the difference of wellhead pressure with various conditions; especially researches the change of wellhead pressure with different fracture length or fracture width under fracturing condition; Lastly, it uses theoretical production under the fixed bottomhole pressure as evaluation index to analyse the better fracture length and fracture width of fracturing in heavy oil reservoir for steam injection. From the study, with the increase of steam injection rate, the wellhead pressure increases; with the increase of steam injection days, the wellhead pressure increase quickly in the beginning of steam injection, and then the rising tendency changes slowly; with the increase of soak days, the wellhead pressure quickly decreases, and then the tendency also changes slowly; Compare with the situation of the fracturing and no fracturing, the wellhead pressure of fracturing are less than the wellhead pressure of no fracturing in any conditions, and the longer the fracture length or the wider the fracture width, the lower the corresponding wellhead pressure; Finally, it analysises the better fracture length and fracture width of fracturing about heavy oil by using the calculated results of theoretical production.