Stress redistribution in multi-stage hydraulic fracturing of horizontal wells in shales

Abstract

Multi-stage hydraulic fracturing of horizontal wells is the main stimulation method in recovering gas from tight shale gas reservoirs, and stage spacing determination is one of the key issues in fracturing design. The initiation and propagation of hydraulic fractures will cause stress redistribution and may activate natural fractures in the reservoir. Due to the limitation of the analytical method in calculation of induced stresses, we propose a numerical method, which incorporates the interaction of hydraulic fractures and the wellbore, and analyzes the stress distribution in the reservoir under different stage spacing. Simulation results indicate the following: (1) The induced stress was overestimated from the analytical method because it did not take into account the interaction between hydraulic fractures and the horizontal wellbore. (2) The hydraulic fracture had a considerable effect on the redistribution of stresses in the direction of the horizontal wellbore in the reservoir. The stress in the direction perpendicular to the horizontal wellbore after hydraulic fracturing had a minor change compared with the original in situ stress. (3) Stress interferences among fractures were greatly connected with the stage spacing and the distance from the wellbore. When the fracture length was 200 m, and the stage spacing was 50 m, the stress redistribution due to stage fracturing may divert the original stress pattern, which might activate natural fractures so as to generate a complex fracture network.

Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production

“…In both exploration and production of shale gas, brittleness and ductility of shale are important evaluation parameters as they are closely related to natural shale fracture (Ding et al 2012), artificial hydraulic fracturing , drilling (Eshkalak et al 2015;Zeng et al 2015), permeability (Ghanizadeh et al 2013) and gas preservation (Yarali and Kahraman 2011;Gale et al 2014;Hu et al 2015;Liu and Sun 2015;Zeng et al 2015). Brittleness is one of the most important mechanical parameters of unconventional gas shale reservoir estimation when it comes to hydraulic fracturing (Gasparrini et al 2014;Holt et al 2015) and borehole wall stability assessment and gas preservation risk (Ingram and Urai 1999;Hu et al 2014;Zhou et al 2014).…”

A Model for Multiple Hydraulic Fracture Propagation with Thermo-Hydro-Mechanical Coupling Effects

“…The first case is a vertical fracture case as shown in Figure 4, in which the fracture is imposed a constant fluid pressure inside. The fluid pressure would induce extra stresses around the fracture, and the induced stresses at arbitrary point is given as [34]:…”

Mineral and Fluid Transformation of Hydraulically Fractured Shale: Case Study of Caney Shale in Southern Oklahoma

“…The objective mainly is to stimulate the reservoir formation to create fracture networks and increase the permeability of the formation. These fracture networks subsequently act as pathways for hydrocarbon migration from reservoir to wellbore (Zeng et al 2015). Hydraulic fracturing is an expensive operation, yet sometimes the permeability increases achieved from fracturing operations are short lived due to fracture closures over time, causing rapid decline in production (Alfarge et al 2019).…”