Shadkinsky uplift (Republic of Tatarstan , Russian Federation)
At present, petroleum exploration in Republic of Tatarstan in Russia faces challenges to small oil fields contouring, checking uplifts for the presence of hydrocarbons and searching for various complex traps. Main oil exploration geophysical method – seismic survey is not able to uniquely solve the challenges and there is a need to use non-seismic methods of prospecting and exploration.
In 2008, deep well #635 was drilled within Shadkinskaya structure as a result of seismic explorations conducted earlier. This well gave industrial oil flow from Timan terrigenous sediments of Upper Devonian horizon with 23 m3/day debit. Subsequent Shadkinskoye uplift structural plan refinement based on the drilling results showed that the well had not been placed optimally (at highest hypsometric position of Sargayevski horizon roof) but it had been placed in the southern periclinal part of Shadkinskaya structure. A question raised up quickly: at which direction to perform further drilling?
Electromagnetic exploration conducted by the method of vertical currents sounding (VECS) in 2009 together with «TNG-Kazangeophysica» aimed at contouring the oil deposit. A circular electric dipole (CED) with 1 km long rays was used as a source of excited electromagnetic field. Total current in all rays was maintained at 112 A. To solve the above-stated challenges an electrical survey has been conducted over a sparse grid containing 203 observation points covering approximately 40 km2 area.
Processing and interpretation of the survey results allowed us to refine the forecast, which was based on seismic research. The figure below shows areal distribution of registered VECS signal at 201 ms, which corresponds to the target depth of about 1600 m. Within the positive signal area zones with the highest vertical component level of the magnetic field are highlighted. These zones are the most promising for oil.
The figure below shows the apparent cross-section along one of the profiles. As the time of registration (sounding depth) grows, signal anomaly caused by the halo is shifted horizontally.
Recently an interesting confirmation of this anomaly was received from quite unexpected source. Geochemical survey was carried out on the site and geochemical anomaly is very close to the VECS anomalies. We traced the halo came to the surface! Thus, we can characterize the VECS methodology as a direct method for determining hydrocarbons, based on the direct fixation of the signals caused by aureole changes above the deposit.
Articles
V.S. Mogilatov, A.V. Zlobinskiy. The complex prospecting of a variety of electromagnetic parameters of the medium above seismic uplifting for the detection of oil deposits. // Geophysics, 2013, No. 2, p.51-57 1 Мб, pdf-file
About VECS
Electrical prospecting by the method of vertical electric current sounding (VECS) as applied to oil targets. 2 Мб, pdf-file