Combination of Geomechanics, Stress Field with Reservoir Static and Dynamic Performance to Characterize Dynamic Fractures in Ultra-low Permeability Reservoirs

Abstract

Along with the long-term water flooding, dynamic fractures developed in the ultra-low permeability reservoirs. The hydraulic fractures in near wellbore area of injection or production wells extend forward under the control of current stress field, until connecting with natural fractures which is forming from paleo-stress field. These dynamic fractures severely affected the water-flooding development efficiency of low permeability reservoirs. In this paper, an integrated approach is proposed and applied to a tight sandstone reservoir as a case study. The geomechanics model is first built up to predict potential natural fractures distribution under the paleo-stress field. Then hydraulic fractures parameters are obtained from operation and monitoring data of hydraulic fracturing. Also, the extended pressure of dynamic fractures is calculated by geomechanic experiment results. Finally, the dynamic fractures model is built up by integrating natural fractures model, hydraulic model, and extended pressure value. The results indicate that the natural fractures form in the period of Yanshan and Xishan periods with predominant orientation of NE60–70. The fracture model is built up by finite element simulation. Artificial fractures extend by the orientation of NE46.4–75.1 with length around 162 m. The extension pressure was nearly the same as minimum principal stress (20 MPa) especially when natural fractures developed in the reservoir. Meanwhile well test showed that reservoir pressure monitored from more than 22 wells reached higher than 19.8 Mpa and that fractures half-length extended longer than 100 m. The complexity of dynamic fractures was influenced by lithology-based geomechanics, paleo and current stress field, varied production performance, which are necessary to predict dynamic fractures distribution.