The industrial oil-shale bed of the Leningradskoye field is confined to the Kukruse horizon of Ordovician limestones. The thickness of the overlying strata varies from 50-60 m in the north to 80-100 m in the south. In the northern part, Ordovician limestones occur directly under Quaternary sediments; in the southern part, in addition to Quaternary sediments, they are overlain by Middle Devonian sediments (marls, sands and clays). The thickness of Quaternary sediments is on average 5-10 m.
The method of combined electro-profiling was first proposed in 1937 by A. S. Semenov. Laboratory and field experimental works carried out by him and N. P. Grigorieva showed high efficiency of the method when searching for wellconducting steeply dipping ore bodies occurring in electrically homogeneous medium.
