Abstract
Whether intentionally or unintentionally, waterflooding always takes place under fracturing condition in tight reservoir because of the extremely limited water absorption ability of the formation. Recently, we proposed a novel workflow, including real-time monitoring, formation testing analysis, and dynamic production analysis, to timely and effectively identify the initiation of waterflood-induced fractures (WIFs) and characterize the waterflooding behaviors for a well group. In this paper, we further provide a supplementary study to evaluate the waterflooding performance from the well group to the field basis. The utilization factor (UF) is first estimated on the basis of injection/production data by material balance theory, which provides an overall picture of water injection efficiency every year. Then, the areal (straightforwardly showed by water cut and formation pressure distributions) and vertical sweep (includes the water absorption in injectors and water breakthrough in producers) behaviors are studied to investigate the waterflooding characteristics and residual oil distributions. Lastly, three key influence factors are detailedly discussed: sand body connectivity, WIFs, and injection and production correspondence. Combining the previous work for the single well group, and the study in this paper to field basis, one can have a better and much more comprehensive understanding of the waterflooding performance and then thus take the corresponding adjustment measurements to improve waterflooding effectiveness.
Highlights
China University of Petroleum, Beijing and State Key Laboratory of Petroleum Resources and Prospecting, Beijing, China
The utilization factor (UF) is first estimated on the basis of injection/production data by material balance theory, which provides an overall picture of water injection efficiency every year
Lots of producers watered out very quickly and unexpectedly in the early 2014. This may be caused by waterflood-induced fractures (WIFs), which keep closed in the original state, and expand and extend if the reservoir pressure is larger than fractureinitiation pressure [1,2,3,4]
Summary
Block D is a typical tight oil reservoir in Changqing Oil field, China. It was put into production in 1995, and the advanced water injection was applied in 2002 to maintain the reservoir pressure because of the low pressure coefficient. Lots of producers watered out very quickly and unexpectedly in the early 2014. This may be caused by WIFs, which keep closed in the original state, and expand and extend if the reservoir pressure is larger than fractureinitiation pressure [1,2,3,4]. Combining the methodology proposed in this paper and the workflow presented before [7], one can have an overall understanding of the waterflooding performance (Figure 1)
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