Assessment of Reactivated Natural Fractures Influence on Overall SRV During Multi-Stage Hydraulic Fracturing

Abstract

This work is devoted to the development of methods for determining the stimulated reservoir volume (SRV) taking into account the contribution of natural fractures hydrodynamically not connected with technogenic one with the example of Western Siberia reservoir. At present, more and more fields with a complex geological structure, including low-permeability reservoirs, require effective technologies for exploitation, which in turn has led to the massive applying of horizontal wellbores and technologies of multistage fracturing. Modeling of multistage fracturing is a complex process that requires an understanding of the mechanical behavior of the formation, cracks and faults. The cracks formed during the hydraulic fracturing change the stress field around it, this effect is called the shadow stress effect. Natural fracturing can have a significant effect on production rates, in particular, on the hydrodynamic connection of the reservoir and the migration path of fluids. If stress shadow effect of the technogenic fracturing is taken into account, then can be additionally taken into account the reactivated natural fractures with induced stresses as well. In the process of the work, mechanisms of formation of natural fracturing were determined on the basis of seismic attributes and reconstruction of paleostresses, a natural fracture network model was constructed using geomechanical information. The results obtained during the construction of a NFN play one of the key roles for the modeling of the multistage fracturing in fractured reservoirs allows to take into account information on the intensity and direction of development of natural fracturing in addition to mechanical properties: elastic and strength characteristics of rocks. In this paper, we demonstrate the results of a numerical evaluation of multistage fracturing influence in the change of the stress field. The stress field, modified during the stimulation, was used to assess the critical stress fractures, which allows increasing the stimulated reservoir volume due to reactivated natural fractures. Such cracks do not need to be fixed, since they are formed by sliding along the plane of failure with small changes in the stress field and give an additional contribution to the total area induced fractures. The demonstrated technique allows to maximize the area of induced fractures and increase the stimulated reservoir volume by taking into account the critically-stressed one.