Study on Development Well Pattern of Combined Steam Drive and Gravity Drainage in a Reservoir with Interbeds and its Application: A Case Study

摘要

SAGD with combination of vertical and horizontal well has been commercially applied in Liaohe Oilfield. The medium-depth massive super heavy oil D-X reservoir with edge and bottom water is the object of this study. As there exist several extensive interbeds above the horizontal section, the steam chamber is not able to spread to the oil zones above them, resulting low producing degree of the reservoir, and the indicators of development plan cannot be met. To overcome the present problems, a novel SAGD well pattern was proposed, in which oil is drained vertically and swept horizontally at the same time. A high temperature and high pressure physical model was used to simulate the process of SAGD with combined steam drive and gravity drainage (hereinafter refers to as "CSDGD") in a reservoir containing interbeds. It was observed that the steam chamber fully spread when steam is injected and oils produced above the interbed using vertical wells while producing the reservoir with SAGD under the interbeds. In this way, reserve in the model was sufficiently produced. The width and length of interbeds and its distance to horizontal well are the main factors affecting development effect. The further step is to build numerical model of interbeds of different width, length and vertical position to investigate the effects of interbed distribution and development on SAGD. Finally, screening criteria were proposed for CSDGD and well pattern of steam flooding above the interbed was optimized as well. At present this technique has been applied in 19 well groups in D-X Reservoir. Well temperature monitoring data shows that reservoir temperature above the interbeds was increased significantly from 70°C to 250°C. The oil production rate of well group was increased from 15t/t to 30t/t; the oil-steam ratio was increased by 0.02 ~ 0.03. Vertical producing percentage was increased by 20%. A new SAGD well pattern was proposed for the reservoir with interbed in this paper, and the mechanism is revealed. This technique has been successfully used in D-X reservoir to overcome the unfavorable effects of interbeds on steam chamber forming. The study results can be applied to the SAGD development block that cannot meet economic indicators due to the effects of interbeds.