Abstract
Hall plot analysis, as a widespread injection evaluation method, however, often fails to achieve the desired result because of the inconspicuous change of the curve shape. Based on the cumulative injection volume, injection rate, and the injection pressure, this paper establishes a new method using the ratio of the pressure to the injection rate (RPI) and the rate of change of the RPI to evaluate the injection efficiency of chemical flooding. The relationship between the RPI and the apparent resistance factor (apparent residual resistance factor) is obtained, similarly to the relationship between the rate of change of the RPI and the resistance factor. In order to estimate a thief zone in a reservoir, the influence of chemical crossflow on the rate of change of the RPI is analyzed. The new method has been applied successfully in the western part of the Gudong 7th reservoir. Compared with the Hall plot analysis, it is more accurate in real-time injection data interpretation and crossflow estimation. Specially, the rate of change of the RPI could be particularly suitably applied for new wells or converted wells lacking early water flooding history.
Highlights
Chemical flooding, a rapidly developed tertiary oil recovery technique, is applied successfully and widely both in the Daqing Oilfield and the Shengli Oilfield (Zhang et al 2010; Hou et al 2011, 2013; Shaker Shiran and Skauge 2013; Dag and Ingun 2014)
Based on the cumulative injection volume, injection rate, and the injection pressure, this paper establishes a new method using the ratio of the pressure to the injection rate (RPI) and the rate of change of the RPI to evaluate the injection efficiency of chemical flooding
Compared with the Hall plot analysis, it is more accurate in real-time injection data interpretation and crossflow estimation
Summary
A rapidly developed tertiary oil recovery technique, is applied successfully and widely both in the Daqing Oilfield and the Shengli Oilfield (Zhang et al 2010; Hou et al 2011, 2013; Shaker Shiran and Skauge 2013; Dag and Ingun 2014). The Hall plot analysis was firstly used to evaluate the performance of waterflood wells (Hall 1963) and gradually was used as a simple, effective method for diagnosing the injection efficiency (DeMarco 1969). Considering that the reservoir permeability is an important factor affecting the resistance factor, Kim and Lee (2014) used the effective permeability changing with the water saturation instead of regarding permeability as a constant, improving the accuracy of the Hall plot analysis. As the change of the slope in the Hall plot is usually not significant in the early period of chemical flooding, it is hard to use the Hall plot analysis to obtain the resistance factor. A new method, derived from injection performance data, is proposed for the real-time characterization of the chemical flood. The dynamic data of this pilot test are used to verify the new method
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