Vinokurovsky site (Tatarstan republic, Russia).
Survey works were conducted by the order of “TNG-Kazan’geofizika“ on the ground of Republic of Tatarstan, Russia.
At the present time, the problems of delineation of small oil deposits, inspection of seismic uplifts for availability of hydrocarbons, and prospecting for structurally complex hydrocarbon traps of various kinds would be most acute in surveys for oil on the ground in Republic of Tatarstan. The main geo-physical oil exploration method such as seismic exploration is unable to solve these challenges unambiguously and there is imperative that prospecting and exploration methods different from seismic ones should in invoked.
Surveying by vertical electric current sounding was performed to evaluate the prospectivity of a group of seismic uplifts on the Vinokurovsky site. The area of the electrical prospecting works was 13.5 km2. Within the bounds of the area, 137 measurements of the vertical magnetic induction velocity when the electromagnetic field is excited by a circular electric dipole (CED) with the radius of 500 m.
Beyond the projected area, 67 measurements were taken, which allowed delineation of the north boundary of the oil field. The distance of measurement points from the CED center was up to 3 км (6 CED radii).
As a whole, a sharp separation of the structure of the VECS electromagnetic response was observed on the area of electrical prospecting by vertical electric current sounding. Increased positive EMF values were specific for the south-western part of the area. We associated this fact with the influence of hydrocarbons on the host medium. For the north-eastern part of the area, negative EMF values were observed (no mass availability of hydrocarbons). Within the bounds of the area with negative EMF values, the well 560 was located. This well was drilled to the depth of 1857 m and it didn’t tap oil-saturated strata. In boreholes 582, 634, 658 and 669 within the bounds of positive EMF values, com-mercial oil inflows (from 5 to 8.5 ton per day) were obtained and the region most prospective for re-vealing oil pool, which covers the area of positive values of signals with the intensity more than 0.1 , had been distinguished. According to the obtained data, the southern part of the exploration area is the most prospective for revealing oil accumulation in Lower Carboniferous deposits.
The group of seismic uplifts in the CED region for evaluation of prospectivity of which these works were directed using electrical exploration data by VECS turned to be not very prospective for revealing hydrocarbons in Lower Carboniferous deposits. The potentially oil-bearing area in the Lower Carboni-ferous deposits had been isolated in the south-western part of the exploration area.
Effect of topographical relief.
When survey works by the VECS method were carried out, operators were frequently faced with complications of the topographical relief. If the influence of the relief was significant, then this fact was taken into consideration in data processing. Hydrocarbons which are usually studied are deeply buried. Accordingly, signals associated with influence of hydrocarbons usually correspond to late times. Most commonly, when a transient process in the earth proceeds at late times, the effect of relief is not signif-icant and it may be neglected. However, it was just the Vinokurovsky site where the CED, in virtue of a number of limitations, was mounted ineffectually.
For evaluation of the effect of topographical relief on the CED signal and introduction of correction for the relief, 3D modeling had been executed. Parameters of the horizontally-layered medium were taken in accordance with the interpretation results of TDEM soundings. The results of the 3D modeling showed that the anomaly induced by the topographical relief is the most intensive at the early times (3 ms), comparable with the VECS signal at time 10 ms, and quickly decays at time more than 10 ms. A calculated signal induced by the topographical relief inhomogeneities of the Vinokurovsky site was subtracted from the observed signal. After application of the correction for the topographical relief, contour plots of the VECS signal at times 43.4, 111 and 181ms were constructed.
Areal results of VECS surveying at time 111 s
Plot of emf contours at time 111 s. Correction for topographical relief was applied.
Scale 1: 25000
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 Mb, pdf-file
About VECS
Electrical prospecting by the method of vertical electric current sounding (VECS) as applied to oil targets. 2 Mb, pdf-file