Methodical aspects of studying mechanical properties of rocks of Bazhenov formation

UDK: 552.08
DOI: 10.24887/0028-2448-2020-3-43-46
Key words: core, geomechanics, Bazhenov formation, research, rocks, sample preparation
Authors: A.A. Shubin (Tyumen Petroleum Research Center LLC, RF, Tyumen), A.Yu. Kudymov (Tyumen Petroleum Research Center LLC, RF, Tyumen), V.M. Yatsenko (Rosneft Oil Company, RF, Moscow)

The study of mechanical properties on the core allows us to evaluate the conditions under which plastic and elastic deformations occur in the formation. In combination with information about the material composition, the degree of transformation of organic matter, reservoir pressures, and tectonic activity within the area, this is the basis for creating promising geomechanical models. The results of core testing largely depend on the conditions of research, which, in turn, should be as similar as possible to the conditions of natural occurrence. Given the complex conditions of occurrence and textural and structural properties, a number of questions arise with regard to methodological approaches to sample preparation and research of geomechanical properties of rocks of the Bazhenov formation, taking into account all the features of oil-bearing rocks: their composition, type of cementation, wettability, saturation, and other physical and chemical properties.

 On the example of the results of laboratory tests, differences in the results of determining the deformation and strength properties in accordance with domestic (GOST) and foreign (ASTM) standards are shown. Optimal axial loading speeds are set ((0.5 – 1)·10-5 C-1) and the effect of sample saturation on their elastic-strength properties. In order to make the most accurate assessment, the thermodynamic conditions of testing were as close as possible to the conditions of natural rock occurrence, taking into account the abnormal-high formation pressure and the anisotropy of the stress state of the array. Special attention is paid to the importance of conducting x-ray computed tomography of the core column and samples before testing. Among other things, this technology can reduce the number of defects in the manufacture of cylindrical samples by 20-30% and improve the accuracy of the assessment of geomechanical characteristics.

References

1. Kalmykov G.A., Kiryukhina T.A., Korobova N.I. et al., Regularities of structure of Bazhenov horizon and upper parts of Abalak suite in view of oil production prospects (In Russ.), Geologiya nefti i gaza, 2013, no. 3, 14 s.

2. Moronkeji D.A., Prasad U., Franquet J.A., Size effects on triaxial testing from sidewall cores for petroleum geomechanics, ARMA-2014-7405, 2014.

3. Ostapchuk M.A., Kuznetsov V.A., Antonenko A.A. et al., The synergy of geological and technological aspects is the key to successful fracturing of the source rocks (In Russ.), SPE-182078-RU, 2016.

4. Zoback M.D., Geomekhanika neftyanykh zalezhey (Reservoir Geomechanics), Stanford University, California, 2007, https://doi.org/10.1017/CBO9780511586477.

5. Tiab D., Donaldson E.C., Theory and practice of measuring reservoir rock and fluid transport properties, Gulf Professional Publishing, 2004, 880 p.

6. Longyun Zhang, Shangyang Yang, Study on temperature-time effect characteristics of hard rock under long-term load, ARMA-2019-2158, 2019.

The study of mechanical properties on the core allows us to evaluate the conditions under which plastic and elastic deformations occur in the formation. In combination with information about the material composition, the degree of transformation of organic matter, reservoir pressures, and tectonic activity within the area, this is the basis for creating promising geomechanical models. The results of core testing largely depend on the conditions of research, which, in turn, should be as similar as possible to the conditions of natural occurrence. Given the complex conditions of occurrence and textural and structural properties, a number of questions arise with regard to methodological approaches to sample preparation and research of geomechanical properties of rocks of the Bazhenov formation, taking into account all the features of oil-bearing rocks: their composition, type of cementation, wettability, saturation, and other physical and chemical properties.

 On the example of the results of laboratory tests, differences in the results of determining the deformation and strength properties in accordance with domestic (GOST) and foreign (ASTM) standards are shown. Optimal axial loading speeds are set ((0.5 – 1)·10-5 C-1) and the effect of sample saturation on their elastic-strength properties. In order to make the most accurate assessment, the thermodynamic conditions of testing were as close as possible to the conditions of natural rock occurrence, taking into account the abnormal-high formation pressure and the anisotropy of the stress state of the array. Special attention is paid to the importance of conducting x-ray computed tomography of the core column and samples before testing. Among other things, this technology can reduce the number of defects in the manufacture of cylindrical samples by 20-30% and improve the accuracy of the assessment of geomechanical characteristics.

References

1. Kalmykov G.A., Kiryukhina T.A., Korobova N.I. et al., Regularities of structure of Bazhenov horizon and upper parts of Abalak suite in view of oil production prospects (In Russ.), Geologiya nefti i gaza, 2013, no. 3, 14 s.

2. Moronkeji D.A., Prasad U., Franquet J.A., Size effects on triaxial testing from sidewall cores for petroleum geomechanics, ARMA-2014-7405, 2014.

3. Ostapchuk M.A., Kuznetsov V.A., Antonenko A.A. et al., The synergy of geological and technological aspects is the key to successful fracturing of the source rocks (In Russ.), SPE-182078-RU, 2016.

4. Zoback M.D., Geomekhanika neftyanykh zalezhey (Reservoir Geomechanics), Stanford University, California, 2007, https://doi.org/10.1017/CBO9780511586477.

5. Tiab D., Donaldson E.C., Theory and practice of measuring reservoir rock and fluid transport properties, Gulf Professional Publishing, 2004, 880 p.

6. Longyun Zhang, Shangyang Yang, Study on temperature-time effect characteristics of hard rock under long-term load, ARMA-2019-2158, 2019.



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