Experimental investigation of hydraulic fracture propagation in fractured blocks

Abstract

Natural fractures in reservoirs can be the cause of many adverse effects during hydraulic fracturing treatment. In the present paper, hydraulic fracturing tests are used to investigate the interaction of a propagating hydraulic fracture with a natural fracture in the fractured blocks. Systematic experiments were designed and performed on the cement blocks with different pre-existing fracture strikes and dips (30°, 60°and 90°). The effect of horizontal stress difference on the propagation of hydraulic fractures was also determined through a series of experiments with different values for Dr, which were 5 and 10 MPa, respectively. Propagation arrest of the hydraulic fracture and crossing the pre-existing fracture were two dominating fracture behaviors at horizontal stress differences of 5 and 10 MPa, respectively. It was observed that both the magnitude of differential stress and the preexisting fracture geometry can magnify the effect of a preexisting fracture on hydraulic fracture propagation. When the horizontal differential stress is low (5 MPa), the hydraulic fracture crosses the pre-existing fracture at a high pre-existing fracture dip (90°) and at an intermediate to high pre-existing fracture strike (60°-90°), while hydraulic fracture is arrested by the opening of the pre-existing fracture at a pre-existing fracture strike (30°). Meanwhile, when the pre-existing fracture dip is low to intermediate (30°-60°) and its strike is low to high (30°-90°), hydraulic fracture is arrested by the opening and shear slippage of the pre-existing fracture in this situation. However, at a high horizontal differential stress (10 MPa), when the preexisting fracture dip is low to high (30°-90°), the hydraulic fracture crosses the pre-existing fracture at the strike of the pre-existing fracture of 60°-90°, and when it is decreased to 30°, the hydraulic fracture is arrested by th eopening and shear slippage of the pre-existing fracture. Therefore, the pre-existing fracture's strike and dip play a significant role in the propagation of hydraulic fracture at a low horizontal stress difference, while the role of the pre-existing fracture dip at a high horizontal stress difference is less than the pre-existing fracture strike on the propagation of hydraulic fracture. Keywords Hydraulic fracture propagation Á Laboratory experiments Á The pre-existing fracture strike and dip Á Horizontal stress difference List of symbols l Fluid viscosity, m/Lt (Pa s) r h Minimum principal stress in horizontal direction, m/Lt 2 (Pa) r H Maximum principal stress in horizontal direction, m/Lt 2 (Pa) r v Principal stress in vertical direction, m/Lt 2 (Pa) D r Horizontal stress difference, m/Lt 2 (Pa) p Fluid pressure, m/Lt 2 (psi) q Flow rate of fluid, L 3 /t (m 3 /s) E Young's modulus of elasticity, m/Lt 2 (Pa) m Poisson's ratio r c Unconfined compressive strength, m/Lt 2 (Pa)

The effect of natural fracture dip and strike on hydraulic fracture propagation

“…Experimentally, several researchers [3][4][5][6][7][8][9][10][11][12][13] have widely investigated the problem of hydraulic and natural fractures interaction to improve the success rate and fracturing effect. On the basis of experimental studies, it is conceivable that several events may occur during the period of hydraulic fracture propagation towards the natural fracture and beyond.…”

Mechanism of fracture initiation and propagation using a tri-axial hydraulic fracturing test system in naturally fractured reservoirs

“…Following the previous experimental works, Warpinski and Teufel (1987), Warpinski (1991), Zhou et al (2008) and Dehghan et al (2014Dehghan et al ( , 2015 conducted many hydraulic fracturing experiments to investigate induced fracture propagation behaviour and fracture geometry in naturally fractured reservoirs. They observed three types of interactions between hydraulic and natural fractures which were crossing, arrest by opening and dilating the natural fracture, and arrest by shear slippage of the natural fracture with no dilation and fluid flow along the natural fracture.…”

“…According to tensile strength criterion, hydraulic fractures on the wellbore wall initiate when the principal tensile stress within the rock (due to the fluid pressure within the rock) exceeds the minimum principal stress plus the tensile strength of the rock (Haimson, 1967;Hossain, Rahman, & Rahman, 1967, 2000Hubbert & Willis, 1957). A series of lab experimental studies have been conducted in the past to investigate the influence of natural fracture on the fracture initiation and propagation under different reservoir conditions (Beugelsdijk, De Pater, & Sato, 2000;Blanton, 1986;Dehghan, Goshtasbi, Ahangari, & Jin, 2014Gu et al, 2012;Olson, Bahorich, & Holder, 2012;Suarez-Rivera, Burghardt, Stanchits, Edelman, & Surdi, 2013;Tie, Wei, & Xueliang, 2011;Warpinski & Teufel, 1987;Zhou, Chen, Jin, & Zhang, 2008;Zhou, Jin, & Chen, 2010). Some experimental investigations (Blanton, 1982;Daneshy, 1974;Lamont & Jessen, 1963) have demonstrated that the advancing induced hydraulic fracture crosses the natural fracture without any significant change in its direction, turns into the natural fracture and dilates it or, in some cases, turns into the natural fracture and beside the dilation of natural fracture, breaks out again by a fracture or flaw along the natural fracture.…”

An Experimental Investigation of Hydraulic Fracturing in Shale Considering Anisotropy and Using Freshwater and Supercritical CO2

“…For decades, laboratory experiments have been used to study hydraulic fracturing using freshwater as a fracturing fluid [3,[16][17][18][19][20][21][22]. Various studies [23][24][25][26][27][28][29] investigated important factors (such as rock structure, in situ stress, viscosity, and the injection rate of a fracturing fluid) that affect the hydraulic fracturing process.…”