The adaptive technology of EM survey of MTS and TEM methods in conditions of inhomogeneous upper part of section of the Siberian platform gives essential improvement of reliability of forecasting the brine-saturated collectors. The accuracy of definition of geometry of axial surfaces of brine-saturated collectors in conditions of traps-reach sections – not worse than 2-4% of depth and in some cases better than seismic CDP method. Now the technology is brought to industrial application. It is patented in Russia and abroad.
Jeldonskaya No.260 parametrical well is located in a joint zone of the Prisayano-Eniseysky syneclise with the Angaro-Lensky step in Eastern Siberia. Oil-and-gas bearing is connected with the Lower Vendian - Lower Cambrian terrigenous part of a section.
As a result of EM-reconstruction of a model of the geological medium in the vicinity of the well (area of 100 sq.km) according to MTS and TEM data it is established that inhomogeneous upper part of a section with a resistance of 100 Ohm⋅m has high-conductivity blocks with a resistance down to 1 Ohm⋅m which complicate parametrization of the target horizons at depths more than 3000 m.
As a result of 3D-reconstruction of MTS + M-TEM data the distribution of resistance in the studied volume that matched to the measured signals for all receiver points over the survey area has been calculated. As a result the conductor layer at depths of 3700-3800 m is identified as a high-permeability collector (ρ=2-5 Ohm⋅m).
This depth interval (3665-3682 m) is presented by coarse-grained, well permeable sandstones with coefficient of porosity of 9.35-16% from which water inflow of rate of 300 m3/hour is received. The relative error of determination of depth of an axial surface of this well-conductivity layer has been estimated at level of 1.5% (or 38 m).
Drilling of the Zheldonsky well has confirmed the permeable terrigenous collector revealed earlier according to electromagnetic survey.
Chaykinskaya No. 279 parametrical well is located on the Chaykinsky uprise in a zone of a joint of the Nepsko-Botuobinsky anteclise with the Predpatomsky regional depression in Eastern Siberia. Oil-and-gas bearing is connected with a high-permeability collector in Vendian - Lower Cambrian carbonate part of a section.
As a result of EM-reconstruction of model of the geological medium it is established that without accounting of the upper part of section there is no chance to trace the target horizons easily: they are "scattered" on separate fragments due to unaccounted influence of the upper part. 3D-reconstruction on all area aperture (S=100 sq.km) with accounting of the upper part has allowed to allocate the second target conductive horizon (the first one is at depths of 750-900 m, and the second - at depths of 1500-1650 m). The following drilling in 2009-2010 has confirmed this forecast. Tests in a cased well have given stable inflow of water and gas from the layer of fractured dolomite.
EM-researches by M-TEM method at Chaykinskaya area have allowed to localize the area of spreading of the target horizon in the plan and by depth. The relative error of determination of depth of an axial surface of brine-saturated collector has been estimated at level of 3.8% (or 60 m).
No.1 exploration-appraisal well is located on the western slope of the Nepsko-Botuobinsky anteclise in Eastern Siberia. Oil-and-gas bearing is connected with high-permeability terrigenous collectors of Vendian and Vendian - Lower Cambrian carbonate collectors.
On the most part of the area the upper part of a section is represented by the high-conductivity deposits of Permian and Carboniferous, Jurassic deposits having resistance of the first units of Ohm⋅m, obstructing the allocation of the target horizons. Therefore at the initial stage the volume reconstruction of a model of the upper part of section for the whole area of research (S=2760 sq.km) has been provided. Such accounting has allowed to allocate and localize a zone of a high-permeability collector which corresponds to a total contribution of the lower part of Usolsky series and Vendian part of a section at a depths of 2100-2400 m. Total thickness of the allocated interval is about 300 m, longitudinal resistance – from 2 to 10 Ohm⋅m. Within this zone a hydrocarbon trap connected with a nipping of collectors in vanavarsky, sobinsky and tetersky series (ust-kutsky horizon) in a zone of an adjunction to the base ledge is delineated. The place for drilling of a well is recommended.
The following drilling in 2014 has confirmed this forecast. Within the trap the well has been drilled down to the depth of 2578 m, terrigenous deposits of Vendian, a roof of Riphean were stripped. Five objects are tested: in deposits of the osinsky horizon and tetersky, sobinsky, katangsky, oskobinsky and vanavarsky series. During test of the well the inflows of reservoir water with the small content of the dissolved gas from tetersky (interval of 2198-2229 m), sobinsky (interval of 2262-2273 m) and oskobinsky (interval of 2413-2421 m) series are received. From vanavarsky series insignificant inflows of reservoir water are received because of argillization of the section.