PSI - Issue 6

I. Bazyrov et al. / Procedia Structural Integrity 6 (2017) 228–235 Author name / Structural Integrity Procedia 00 (2017) 000–000

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Figure 6. Mohr’s’ diagram (n, τ – normal and tangential stress tensor components on fracture face).

Micro-seismic observation Micro-seismic observation is one of the most informative methods for determining the parameters of fracture zones that arise during hydrofracturing. Other methods have either low reliability (modeling, tracer studies, tiltmeters) or give the information about the parameters of fractures only in the near-wellbore area (temperature logging, cross-dipole acoustic broadband logging, pressure transient analysis). During the process of hydrofracturing rock deformation takes place. As a result, deformation energy is released in the form of elastic waves. Waves propagate along the trajectories in accordance with the velocity model of the medium and can be recorded in a neighboring observation wells or on the surface. By focusing the sources of elastic waves, it becomes possible to estimate the 3D geometry of the artificial fracturing zone formed during hydraulic fracturing. Evaluation of hydraulic fracturing crack reorientation requires from micro-seismic observation an increased accuracy in determining the point of fracture initiation and its orientation. In order to solve this problem correctly, it is necessary to perform calibration explosions in the stimulated well (cumulative perforations, detonation cord), which allow to calibrate the a priori velocity model and significantly improve the accuracy of the fracture geometry determination. In the absence of calibration, the error in determining the point of fracture initiation can reach 100 meters. The implementation of well monitoring with one observation well leads to an increase in the error at the far ports (Figure 7), which must be taken into account during the data interpretation.

Figure 7 . Micro-seismic observation. Map of uncertainties in azimuth and distance (plan view). The main problems that arise in the process of micro-seismic monitoring are related to quality control of performed work. The difference in algorithms of data processing and the lack of information about the limitations of the imaging technique (implemented in specific geological conditions) often lead to a low quality of the results. Therefore, it is important to characterize possible uncertainties at the stage of planning and design, correctly set the research task and perform the maximum possible set of quality control procedures, starting with the field design and ending with the interpretation of the results. The process of micro-seismic monitoring is described in details in [13]. Conclusion The article considers the time-dependent hydro-geomechanical reservoir model (4D) for field production. It is shown that coupled hydro-geomechanical reservoir model makes it possible to simulate principal reservoir stresses reorientation during the pore pressure change. Accurate assessment of stress orientation change can be helpful for re-fracturing planning. Stress alteration can be used to increase production and decrease the number of drilling wells by propagating new fractures into undepleted zones.