A prediction model of breakdown pressure of wellbore-perforation formation based on elastic-plastic around wellbore
The"high geostress,high temperature,and high formation pressure"conditions in the deep part of the reservoir make the reservoir show the plastic characteristics of brittle-ductile-strain hardening.Hydraulic fracturing for deep plastic reservoirs presents challenges of artificial fracture initiation and high extension pressures.In this paper,the plastic failure characteristics of reservoir rocks are clarified by conducting real-time triaxial compression experiments with high temperature and high confining pressure.Based on the experimental results,the corresponding plastic hardening constitutive model is proposed,and the distribution of elastic-plastic stress field around the wellbore is established.Based on the theory of fracture mechanics and considering the influence of plastic zone on the distribution of stress field around the wellbore,the calculation model of fracture toughness of perforation tip in the elastic-plastic stress field around the wellbore is derived,and the corresponding iterative solution method is proposed.The model is used to predict the fracture initiation pressure in laboratory experiments and actual conditions of an oilfield in Xinjiang.The comparison between the model prediction results and the measured results shows that the predicted value of fracture pressure considering the elastic-plastic stress field around the wellbore is higher than the actual fracturing pressure,and the plastic characteristics of the reservoir are not conducive to the initiation of hydraulic fractures.The error between the predicted value of the model and the measured result is 6.6%,which verifies the reliability of the model.The fracture pressure prediction model considering the elastic-plastic around wellbore can ensure the safety of fracturing design and provide effective guidance for the design of deep reservoir fracturing schemes.
deep formationbreakdown pressureelastic-plasticstress field around wellborewellbore-perforation
NETL
NSTL
万方数据
维普
