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

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.

Interaction between hydraulic fractures and natural fractures: current status and prospective directions

“…A novel fully coupled 3D GEOS simulation code was developed by Fu et al (2015a) to model HF-NF interaction in 3D space. A 4D near-wellbore Geomechanics simulation of HF-NF interaction was developed by Zhang et al (2015) in the high-pressure, high-temperature (HPHT) KS tight sandstone reservoir, Tarim basin, China. As the effective fracture length increases, there is a rise in borehole internal pressure, which raises the possibility of identifying the fracture initiation point (Tarokh et al 2016).…”

“…Thus, lower friction coefficient and low approach angle will encourage shearing at the NF interface (Chen et al 2014). In the high-pressure, high-temperature (HPHT) KS tight sandstone reservoir, the results show that when the HF propagation pressure does not exceed the normal stress on the NF, the NF plane will likely shear and propagate the tip of the NF (Zhang et al 2015). The auxiliary HF will likely propagate the tip of the shear-activated NF plane, which tends to create new interconnected fractures.…”