Geophysics

Well-logging Lateral Log signals in deviated and horizontal wells (based on numerical modeling data)

Arzhantsev V.S.

A.A. Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, Russia

arzhantsevvs@gmail.com

The accurate estimation of geoelectric parameters which allows to correct petrophysical evaluation of hydrocarbon saturation of composite oil and gas formations drilled by horizontal wells is a difficult task of well logging today. Lateral Log (Russian Log) data can be useful in solving this problem. Lateral log is widely used in well logging for almost 50 years. Also it has a rich interpretation database, but the new data received in highly deviated and horizontal wells demand in a new theoretical base and interpretational technique.

It is necessary to take into account low formation thickness, resistivity distribution from top to bottom of the layers. Deviation of the wellbore, it’s profile ellipticity, low resistivity of drilling mud, eccentricity of the tool and finite sizes of sondes are also affects on Lateral log signals. Therefore the choice of the most appropriate geoelectrical model will significantly improve evaluation reliability of geoelectrical parameters of investigated objects.

There are increasing importance of utilizing Lateral Log within the Complex which is delivered downhole on the drilling tool or tubing (“SKL” tool), including the wells with a horizontal completion.

The objects of this research are geoelectrical parameters of geological features (terrigenous cross-sections of central part of Western Siberia) determined by Lateral logging data in highly deviated and horizontal wells.

It was performed 2D modeling for the oil reservoir which crossing by horizontal well at different positions and performed calculations of sensitivity functions of Lateral sondes to formation parameters also it was created empirical charts for Lateral sondes for 1D homogeneous formations with low mud resistivity.

It was obtained a series of synthetic diagrams in horizontal wells and found strong effect of borehole profile ellipticity and no effect of tool eccentricity on Lateral Log sonde’s signals.

It was found that in highly deviated and horizontal wells Lateral Log curves becomes symmetric relative to the center of observed formation.

Author restored geolelectric parameters for a number of field (practical) diagrams using 3D modeling inversion data.

References:

1. 3D Mathematical Modelling of Harmonic Electromagnetic Fields in Problems of Logging in Deviated-Horizontal Well Surodina I.V., Epov M.I., Martakov S.V. // International Conference on Matematics 2004. Part.2. p. 699-703.

2. Solution of the problem of Lateral Log in deviated wells by integral equation method. Tabarovskiy L.A., Dashevskiy Y.A. Geology & Geophysics, №7. (1976)

3. Apply 2-D Rapid Iterative Inversion for Lateral Resistivity Logs. Wei Yang, Qingdong Shi. SPWLA 40 th Annual Logging Symposium, May 30-June3, 1999

4. Inversion of a Lateral Log Using Neural Networks. Gerardo Garcia and Whitman W.W.,* Walt Whitman Software Inc. 1992

5. Estimation of Resolution of the Electromagnetic Methods. Tabarovskiy L.A., Epov M.I. Geology & Geophysics, №5. (2006)

6. Enhanced Interpretation of Russian and Old Electrical Resistivity Logs Using Modeling and Inversion Methods. Frenkel M. A., Mezzatesta A.G. SPE Annual Technical Conference and Exhibition held in San Antonio, Texas, 5–8 October 1997.