PSI - Issue 6

Chebyshev Igor et al. / Procedia Structural Integrity 6 (2017) 252–258 Chebyshev I.S./ Structural Integrity Procedia 00 (2017) 000–000

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7. Fracture toughness

In the process of hydraulic fracturing jobs simulation the calculated designs are used. Elastic static moduli, minimal horizontal stress and fracture toughness are included into the mechanical, mathematical models of hydraulic fracturing simulators. The fracture toughness, as a rule, is put into simulator as a specific value for each lithotype. This approach may lead to incorrect calculations because it increases uncertainties in the process of preparing to expensive and complicated operation such as hydraulic fracturing. Actually, there are a lot of fracture toughness estimation techniques like SR, CCNBD, CR, SNDB, CB, CT etc. (Fig. 7).

a.

b.

Fig. 7. Fracture surface shapes of DR and CCNBD specimens: a – SR specimen (Short Rod specimen), b – CCNBD specimen ( Cracked Chevron Notched Brazilian Disc specimen) (Cui, 2010).

8. Conclusion

The borehole stability modelling is important for drilling, hydrofracturing and exploitation. In this paper, the laboratory test data of rock were analysed and new methods of reducing uncertainties are proposed. The static and dynamic core mechanical properties measurement of the rocks shows that there are uncertainties in the interpretation and lab experiments. The methods are proposed for allowing dynamic characteristics determination in weakly consolidated reservoirs. The paper analyses laboratory test data of rock dynamic properties. A new method for predicting petrophysical properties was developed. It can be used to predict dynamical properties of rocks while the well is drilled. With this method, geological and engineering survey will become more effective. There is a high forecast power obtained with ANN(R-sqr=0,91 and R-sqr=0,89 for compressional and shear velocity waves, accordingly). ANN showed better results than linear regression. References Brownlee Jason How to One Hot Encode Sequence Data in Python. - July 12, 2017. Cui Zhen-dong A comparison of two ISRM suggested chevron notched specomens for testing mode-I rock fracture toughness [Journal] // International journal of rock mechanics & mining sciences. - 2010. - pp. 871-876. Fjær Erling Petroleum related rcl mechanics 2nd edition [Book]. - Trondheim : Elsevier, 2014. Haykin Simon S. Neural Networks: A Comprehensive Foundation [Book]. - Michigan : Prentice Hall, 1999. - p. 842. Hettema M.H.H. Minimizing coring-induced damage in consolidated rock [Journal] // Society of petroleum engineers. - 2002. Lukin S.V. Borehole stability prediction to avoid drilling failures [Journal] // Neftyanoe hozyaystvo. - 2016. - pp. 70-73. Ovcharenko Yu.V. Experience in 3D geomechanical modeling, based on one of the West Siberia oilfield [Journal] // SPE. - 2016. S.B. Johns D.J. Lewis Improved Pressure Coring In Unconsolidated Sands [Conference] // SPWLA Conference Paper. - 1981. - p. 16. Sa Andrea Nicolino de Coring samples and obtaining geomechanicap properties for wellbore stability analysis in deepwater brazilian horizontal wells [Journal] // SPE. - 1997.