Monitoring waterflooding front based on the three-dimensional direct-current method with steel casing

When using electrical prospecting methods to monitor the front edge of waterflooding in the residual oil development, the electromagnetic responses generated by the high conductivity of the steel casing in the observation area usually obscure the electrical abnormal signal of the formation caused by waterflooding, largely affecting the imaging accuracy. Considering the densely distributed casing wells in the working area, we propose a novel method that steel casing serves as paths not only for transmitting, but also transferring the waterflooding front signals to the observations that are carried out on the surface. As the electric signals going through the steel casing have nearly zero attenuation, we can effectively observe the weak electric signals of underground waterflooding fluids at the surface receivers. To achieve a high-precision simulation of steel casings, we used an electrical conductivity equivalent method to overcome the problem of excessively large comparative geometrical dimensions. Meanwhile, we utilized unstructured tetrahedral grids to accurately model the irregular shape of waterflooding fluids migration. Based on numerical experiments, we analysed the effects of source type, location, and waterflooding depth on the conduction effect of steel casing, confirming that our method can effectively monitor the migration of waterflooding and capture the boundary of the waterflooding front edge.