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Application of three-dimensional spectral models for the purposes of geosteering

UDK: 550.8
DOI: 10.24887/0028-2448-2018-7-70-73
Key words: three-dimensional modeling, geosteering, synthetic log, heterogeneous reservoir, spectral stochastic modeling method, sequential Gaussian simulation, random field
Authors: N.S .Ismagilov (Gazpromneft NTC LLC, RF, Saint-Petersburg), D.S. Mukhamadeev (Gazpromneft NTC LLC, RF, Saint-Petersburg)

Traditionally most software tools for geosteering use the method of comparison of synthetic and actual well logs. The synthetic log is sampled from a two-dimensional reservoir model, which is built based on the log from the nearest (key) well. The actual logging of the horizontal well is compared with the synthetic log and the stratigraphic formation of the model is corrected until the best match of the synthetic and actual logs is obtained. Thus, the estimated stratigraphic position of the wellbore in the reservoir is determined, as well as the forecast of the reservoir structure.

The paper presents a new approach to modeling of highly detailed geological sections of the reservoir along the given horizontal well. The sections are based on three-dimensional geophysical property model, which are simulated by means of spectral simulation method and use data from all surrounding wells. The “spectral” geological sections of the reservoir provide better estimations of the lithological uncertainty and complexity of reservoir and more reliably predict the distribution of geophysical properties in three-dimensional space.

In order to evaluate the new method an experimental software prototype was developed and tested on real field cases. It was shown that spectral sections provide reliable estimations of real reservoir heterogeneity. Furthermore, comparison of real and synthetics well logs showed high degree of efficiency of the spectral method in geophysical property prognosis along drilled well.

Another important feature of the new method is an ability to build geological sections for horizontal wells with large values of deviation from vertical. Currently these wells are geosteered based on section models build consequently on different key wells. This induces additional task of switching between key wells, which can be non-trivial, and causes violation of geological integrity of full cross-section. A real case of such horizontal well, for geosteering of which four different key wells had been used, was presented. The new method was demonstrated to be able to build models of sections preserving geological integrity and lacking the requirement to perform switching between key wells.

Results presented in the paper prove the new method to have high potential in reduction of financial risks, increase the success of geological and technical actions, particularly passing the borehole through the reservoir with the best filtration properties and to achieve the maximum productivity of horizontal wells

References

1. Baykov V.A., Bakirov N.K., Yakovlev A.A., New methods in the theory of geostatistical modelling (In Russ.), Vestnik Ufimskogo gosudarstvennogo aviatsionnogo tekhnicheskogo universiteta, 2010, V. 14, no. 2(37), pp. 209-215.

2. Griffiths R., Well placement fundamentals, URL: http://www. slb. com/resources/publications/books/well_placement_fund. aspx.

3. Baykov V.A., Bakirov N.K., Yakovlev A.A., Matematicheskaya geologiya (Mathematical geology), Part 1: Vvedenie v geostatistiku (Introduction to geostatistics), Moscow - Izhevsk: Publ. of Institut komp'yuternykh issledovaniy, 2012, 228 p.

4. Khasanov M.M., Belozerov B.V., Bochkov A.S., Fuks O.M., Tengelidi D.I., Automated lithologic facies analysis based on the spectral theory (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2015, no. 12, pp. 48-51.

5. Khasanov M.M., Belozerov B.V., Bochkov A.S. et al., Application of the spectral theory to the analysis and modelling of the rock properties of the reservoir (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2014, no. 12, pp. 60-64.



Traditionally most software tools for geosteering use the method of comparison of synthetic and actual well logs. The synthetic log is sampled from a two-dimensional reservoir model, which is built based on the log from the nearest (key) well. The actual logging of the horizontal well is compared with the synthetic log and the stratigraphic formation of the model is corrected until the best match of the synthetic and actual logs is obtained. Thus, the estimated stratigraphic position of the wellbore in the reservoir is determined, as well as the forecast of the reservoir structure.

The paper presents a new approach to modeling of highly detailed geological sections of the reservoir along the given horizontal well. The sections are based on three-dimensional geophysical property model, which are simulated by means of spectral simulation method and use data from all surrounding wells. The “spectral” geological sections of the reservoir provide better estimations of the lithological uncertainty and complexity of reservoir and more reliably predict the distribution of geophysical properties in three-dimensional space.

In order to evaluate the new method an experimental software prototype was developed and tested on real field cases. It was shown that spectral sections provide reliable estimations of real reservoir heterogeneity. Furthermore, comparison of real and synthetics well logs showed high degree of efficiency of the spectral method in geophysical property prognosis along drilled well.

Another important feature of the new method is an ability to build geological sections for horizontal wells with large values of deviation from vertical. Currently these wells are geosteered based on section models build consequently on different key wells. This induces additional task of switching between key wells, which can be non-trivial, and causes violation of geological integrity of full cross-section. A real case of such horizontal well, for geosteering of which four different key wells had been used, was presented. The new method was demonstrated to be able to build models of sections preserving geological integrity and lacking the requirement to perform switching between key wells.

Results presented in the paper prove the new method to have high potential in reduction of financial risks, increase the success of geological and technical actions, particularly passing the borehole through the reservoir with the best filtration properties and to achieve the maximum productivity of horizontal wells

References

1. Baykov V.A., Bakirov N.K., Yakovlev A.A., New methods in the theory of geostatistical modelling (In Russ.), Vestnik Ufimskogo gosudarstvennogo aviatsionnogo tekhnicheskogo universiteta, 2010, V. 14, no. 2(37), pp. 209-215.

2. Griffiths R., Well placement fundamentals, URL: http://www. slb. com/resources/publications/books/well_placement_fund. aspx.

3. Baykov V.A., Bakirov N.K., Yakovlev A.A., Matematicheskaya geologiya (Mathematical geology), Part 1: Vvedenie v geostatistiku (Introduction to geostatistics), Moscow - Izhevsk: Publ. of Institut komp'yuternykh issledovaniy, 2012, 228 p.

4. Khasanov M.M., Belozerov B.V., Bochkov A.S., Fuks O.M., Tengelidi D.I., Automated lithologic facies analysis based on the spectral theory (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2015, no. 12, pp. 48-51.

5. Khasanov M.M., Belozerov B.V., Bochkov A.S. et al., Application of the spectral theory to the analysis and modelling of the rock properties of the reservoir (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2014, no. 12, pp. 60-64.




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