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.