A Study of the Interaction Mechanism between Hydraulic Fractures and Natural Fractures in the KS Tight Gas Reservoir

Abstract

Abstract The KS reservoir is a naturally fractured, deep, tight gas sandstone reservoir under high tectonic stress. Development wells for this reservoir are of depths in excess of 6,500 m TVD. Stimulation is required to provide production rates that sufficiently compensate for the high cost of drilling and completing wells to access this deep reservoir. Hydraulic fracture design and execution must be optimal to ensure economic production. To effectively stimulate a more than 200-m thick sandstone reservoir yielding consistently high performance, it is critical to understand the interaction between hydraulic fractures and natural fractures, as the natural fractures significantly affect the growth and geometry of hydraulic fractures. To this end, a comprehensive study was conducted involving frac pressure analysis of previously stimulated wells, microseismic data analysis, hydraulic fracturing modeling by using a fracturing simulator that honors the natural fracture system, near-wellbore 4D geomechanical simulation of mechanical response of natural fractures during hydraulic fracturing, and large block hydraulic fracturing tests. This study reveals that existing natural fractures results in complexity of hydraulic fracture systems both in the near wellbore region and in the far field region. The complexity in the far field is largely controlled by the intersection angle (defined as the angle between the natural fracture strike and the maximum horizontal stress direction) given the large differential horizontal stress in this field. Based on an understanding of the interaction mechanism, an optimization of the hydraulic fracturing strategy was implemented in KS field. Improvements were made in staging, perforation, diversion, and the pumping schedule, which increased the averaged production rate more than 50% compared with previously stimulated wells.