Surface and borehole electrical measurements

Surface and borehole electrical measurements (SBEM)

Physical principles of the method

SBEM technology is based on high-precision measurements on the surface of an alternating electromagnetic field of an earthed source - an electric dipole placed in a cased well. Changing the position of the electric dipole in the well (above and below the reservoir) and analyzing the distribution of currents on the surface of the earth, the change in the electrical properties of the target horizon is estimated.

A feature of the SBEM application is the use of a special technology that allows markinglow-resistivity layers in a high-resistivitybackground medium. This technology is a reliable tool for detecting low-resistivity intervals in the thickness of salt-bearing deposits, as well as for studying pre-salt boundaries in the inter-well space. The detection of low-resistivity intervals in the thickness of a high-resistivity background medium is based on the following principles: 

- The base (starting) geoelectric model is formed. It is given in the form of a geoelectric model of the background medium and the geoelectrical model of the search facility (for the layer, the predicted resistance value is specified);

- The cross section of the pseudo-electrical logging curves is plotted according to the SBEM data according to the following scheme: in each picket of SBEM observations, the theoretical electromagnetic field curve for a homogeneous half-space is calculated from the starting model and the curve of the interval resistance R (H) is calculated from the ratio of the field curve to the theoretical signal.Further from the curves of the interval resistance, a low-frequency component is subtracted along the profile, and the remaining high-frequency component is the magnitude of the difference between the real electrical resistance and the one determined in the starting model. Further, the high-frequency component of the interval resistance in each PC is added to the corresponding path of the starting model.Further, the high-frequency component of the interval resistance in each observation point is added to the corresponding path of the starting model. As a result, according to the SBEM data, a section of pseudo-electrical logging curves(PEC-section) is formed in the cross-section, reflecting the lateral variability of resistance in the intersaltinterlayers and the zones of lower resistance values (less than 10 Ohm for AGCF), the presence of brine is predicted.

Problems solved by the SBEM method

- construction of interval geoelectric section in the inters well space;

- detection of brine-saturated layers in the thickness of halogen deposits;

- determination of the distribution of the deposit in the inter-wellbore space

Experience in performing work with the method of SBEM

Throughout 2016-2017 years on the territory of the Astrakhan region 4 production wells were investigated by the SBEM method.