Conditions of Secondary Fracture Reorientation for Cases of Vertical and Horizontal Wells

An approach to determine stress field near wellbore with existing hydraulic fracture accounting for rising pressure and fluid filtration along the crack has been developed. An estimations of secondary fracture initiation time near wellbore as well as moment of primary crack growth start have been produced. Factual data about mechanical rock properties, stress state and pore fluid pressure was used. It has been shown finally that reorientation of secondary fracture in the case of vertical well is improbable during reinjection. Calculations were made with various magnitude and rate of pumping pressure increasing, value of pore pressure inside formation and main tectonic stress ratio acting at infinity. Similar analysis in the case of horizontal well demonstrated several alternative mechanisms of secondary fracture initiation: simulteniously with existing crack growth new fractures along and orthogonal to well trajectory may appear. Which of type will become dominant depends on actual geomachanical conditions and primary fracture characteristics. Obtained estimations have been compared with field observations.