Reducing starting depth in the transient electomagnetic method

The article considers the possibilities of reducing the starting depth of studies using the near-field transient electromagnetic method by determining the effective transmitter-receiver offset. The solution of this problem is relevant due to the need to apply inductive electromagnetic exploration using ungrounded multi-offset templates in the climatic conditions of the Arctic. Optimization of the transient electromagnetic method technology in the far and near-field zones will expand the range of explored depths, which is extremely important for studying the accumulations of difficult to recover hydrocarbons located at depths from the first tens of meters to 3–4 km. To solve this problem for a half-space model, mathematical modeling of the transient electromagnetic signals was carried out taking into account the geometric spacing of soundings, which allowed to determine the effective signal offset by solving the inverse problem. On the basis of the mathematical modeling performed, a nomogram of the effective offset dependence on the transmitter loop size and template geometric spacing has been built. The use of the results obtained makes it possible to provide the actual starting depth of electromagnetic soundings from 7–10 m, which significantly increases the range of the studied depths due to the interpretation of the far-field sounding zone.