Numerical simulation of combined observations for borehole-to-surface DC resistivity and time-domain induced polarization and analysis of anomaly identification capability

The borehole-to-surface direct current resistivity method is an important technique for monitoring water injection, gas injection, and hydraulic fracturing during oil and gas field development. It uses casing-based power supply to obtain potentials and resistivity for anomalous-body interpretation. However, because anomalous bodies are interpreted only from resistivity, the interpretation remains non-unique, so new observation techniques are needed. This study introduces induced polarization into the borehole-to-surface direct current resistivity method and proposes a joint borehole-to-surface direct current resistivity and time-domain induced polarization (TDIP) observation technique. Primary-field potentials are acquired during direct-current power supply, and secondary-field decay potentials are acquired after the power is switched off. Joint numerical simulation of borehole-to-surface direct current resistivity and TDIP is performed with the finite-volume method. Apparent resistivity is obtained from the primary-field potential, and apparent polarizability is obtained from the secondary-field decay potential. For typical anomalies during development monitoring, anomalous-body models with different resistivities and polarizabilities are designed, and numerical simulations are used to investigate the apparent resistivity and apparent polarizability characteristics of single anomalous bodies and a multi-anomaly combined model. The results show that the joint borehole-to-surface direct current resistivity and TDIP method identifies different types of anomalies more effectively than the borehole-to-surface direct current resistivity method alone. Moreover, resistivity differences and polarizability differences from two observations better reflect subsurface anomalous bodies and reduce the non-uniqueness of anomaly identification in oil and gas field development monitoring.