The Research On The Fracture Effectiveness Evaluation Using Rock Mechanics

The assessment of fracture fluid conducting capability in reservoirs is of great significance for hydrocarbon production,especially for tight reservoirs with fractures as the main reservoir fluid transport conduits.Borehole imaging logging provides reliable and effective imaging data for identifying and evaluating fractures around the borehole.However,the depth of detection of borehole imaging data is shallow,and it is impossible to determine the extent of fractures extending outside the well.The dipole shear-wave reflection imaging technology has been effectively applied to identify near-well fractures.It can effectively detect the fractures within tens of meters beside the well.Compared with the early unipolar longitudinal wave reflection imaging technology,the new technology can not only effectively increase the detection range of fractures,but also determine the direction of the fractures.but the evaluation of the fluid conducting effectiveness of the formation fractures remains a challenging task.To accomplish this task,this paper proposes a new method for evaluating the effectiveness of near-well fractures using the 3D Mohr circle analysis,as is commonly used in rock mechanics.The fracture orientation and inclination,as obtained from the borehole reflection imaging,are combined with in-situ stress condition to calculate the stress state on the fracture surface,which,when combined with the Mohr-Coulomb failure criterion,determines whether the fracture is under the critically stressed condition and is therefore fluid conductive.Our analysis shows that the 180-degree fracture orientation uncertainty in the dipole shear-wave imaging does not affect the determination of the stress state on the fracture surface in the Mohr circle method,so that the two methods can be effectively combined to form a new method for evaluating the fluid conducting effectiveness of fractures.The application examples from fractured carbonate reservoirs in different regions show the effectiveness of the new evaluation method,and the evaluation results can be used to provide useful information for field development and production planning.