Electromagnetic sounding in deviated and horizontal wells: mathematical modeling and real data interpretation

Abstract

The features of numerical VEMKZ data interpretation in deviated and horizontal wells entering oil-saturated and water-saturated formations are observed. On the basis of mathematical modeling of VEMKZ signals for typical hole path of horizontal wells the effects caused by crossing bed boundaries and thin layers with high resistivity are shown. The influence of electrical anisotropy on signals has been investigated. The influence of borehole rugosities and tool eccentricity was studied. The programs of numerical modeling have been developed at Institute of Petroleum Geology and Geophysics (IPGG) Siberian Branch of Russian Academy of Sciences. Algorithms and methodological procedures are used for numerical interpretation of VEMKZ data (including SKL set data) in case of thin reservoir, electrically contrasting shoulder beds and thin interlayers. The eccentricity, borehole rugosity, sine-shaped and spiral well bore influence on signals was investigated in case of typical hole and tool diameters, the programs of numerical correction have been developed. The fact that influence of electrical anisotropy in deviated well causes apparent resistivity increase is demonstrated. Numerical inversion VEMKZ data obtained in well entering terrigenous reservoir under-lied by thin layer with high resistivity have been processed. Starting model for inversion is generated by taking direct current data into account. Examples of real VEMKZ data interpretation are demonstrated. For investigations in deviated and horizontal wells the approach for finding true formation resistivity in thin reservoir using high-frequency induction measurements was proposed. This approach based on numerical signal modeling for deviated tool in horizontally-stratified earth. Algorithms for electrical anisotropy evaluating and thin-layer parameters estimating are observed.

Effective Electromagnetic Log Data Interpretation in Realistic Reservoir Models

“…High electrical conductivity of drilling mud cause tool eccentricity to influence VEMKZ logs in the borehole [14]. As calculations have it, the bigger the borehole radius is, and the more contrasting are the electrical conductivities and the probe operating frequency, the higher is the influence.…”

“…Identical fluctuations of signals are modeled in constant diameter boreholes, however, the borehole shape can be both sinusoidal and spiral [14]. The fluctuations period is equal to the spiral period in case of spiral borehole shape, while in a sinusoidal borehole it is twice as less than the sinusoid period.…”