A novel method to assess steam injection rate in the steam-flooding process of shallow heavy oil reservoirs

Steam injection rate is an important parameter in the process of steam flooding. An optimal steam injection rate can supply desirable production effects and economic benefits from a reservoir. At present, the methods to determine steam injection rate mainly include empirical and semiempirical methods, but theoretical research methodology still lacks literature in the body of research. In this paper, a method is presented to assess and optimize steam injection rate for shallow heavy oil reservoirs. Considering changes in specific volume and oil–water flow ratio during steam flooding in a shallow heavy oil reservoir, a calculation model is established for the distribution of sweep multiple. By analyzing the distribution of oil saturation from sweep multiple, areas with more than 50 multiples are defined as invalid injection zones. Analysis of the influence of different steam qualities in the steam chamber of the reservoir’s invalid injection zone indicates that there should be an optimal steam quality in the steam chamber to maximize the area of the invalid injection zone. After analysis of the influence of each injection parameter on the optimal steam quality in the steam chamber, results show that a change in steam injection rate does not affect optimal steam quality. However, the actual steam quality in the reservoir’s steam chamber is closely related to the steam injection rate in the production process. Therefore, by comparing the value of actual steam quality in the steam chamber with the optimal steam quality in the steam chamber, the current steam injection rate can be assessed. Applying this method to a well group in Henan Oilfield shows that the current steam injection rate of this well group is relatively small (90 t/d), and that the steam injection rate should be increased to about 120 t/d. The effects of different injection parameters on the optimal steam quality in the steam chamber are analyzed. It is shown that bottomhole steam quality has a significant effect on the optimal steam quality in the steam chamber and that injection time also has an effect on the optimal steam quality in the steam chamber. In the range of common injection parameters, the optimal steam quality in the steam chamber ranges from 0.1 to 0.3. The method is simple to use and can be applied to guide field production.