Experimental study on the effects of pre-cracks, fracturing fluid, and rock mechanical characteristics on directional hydraulic fracturing with axial pre-cracks

Liu, Zhenghe; Wang, Shaohua; Ye, Hailong; Yang, Lusheng; Fan, Feng; Lian, Haojie; Yang, Dinglong

doi:10.1007/s40948-021-00225-w

Cited by 27 publications

(16 citation statements)

References 29 publications

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“…The results show that the higher the degree of reservoir heterogeneity, the higher the viscosity ratio of the optimal displacement fluid to reservoir fluid required for profile adjustment [21][22][23]. When the viscosity ratio of polymer system to underground crude oil reaches 3.0 or more, the polymer system has a stronger ability to expand the swept volume and improve the oil displacement efficiency [24][25][26].…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on Optimization of Polymer Preslug Viscosity of ASP Flooding in Interlayer Heterogeneous Well Group Artificial Sandstone Core

Sun

Ke-sen

et al. 2021

Geofluids

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An artificial sandstone core model of large well group of positive rhythmic heterogeneous reservoir was designed and made for the simulation of ASP flooding experiment in the moderate heterogeneous reservoir. The well layout of one injection and one production was employed for the core model, to simulate the influence of polymer preslugs with different viscosity on ASP flooding effect. The experimental results show that the injectability of the polymer preslug and the effect of relieving the conflict of remaining oil production in each layer are related to the viscosity of the system. In the heterogeneous core model with the coefficient of variation of 0.65, under the constraint of the same amount of polymer agent, the ASP flooding effect of the 0.075 PV, 60 mPa·s polymer preslug was better than that of the 0.093 PV, 40 mPa·s and 0.064 PV, 80 mPa·s polymer preslugs. The change in the viscosity of the polymer preslug did not enable the ASP system to effectively exploit the low-permeability layer though. As the viscosity increased, the pressure difference between injection and production increased; the remaining oil could be exploited effectively at the bottom of the high-permeability layer and the medium-permeability layer as well as the injection end of the medium-permeability layer. If the viscosity is too small, the high-permeability area cannot be effectively blocked by the injected chemical agent, and if the viscosity is too large, the injected chemical agent cannot produce good elastic displacement relationship, which will lead to ineffective chemical agent flow. Therefore, the polymer preslug viscosity of the ASP flooding system should be moderate, and cores with different heterogeneity should have a reasonable viscosity matching range.

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Section: Introductionmentioning

confidence: 99%

Experimental Study on Optimization of Polymer Preslug Viscosity of ASP Flooding in Interlayer Heterogeneous Well Group Artificial Sandstone Core

Sun

Ke-sen

et al. 2021

Geofluids

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“…Brittle, granular materials like proppants and rocks tend to crush, fracture, and fragment instead of plastically deforming when subjected to high stresses [47]. Therefore, understanding proppant-rock fracture initiation, fracture propagation, and fracture coalescence mechanisms during proppant crushing, and capturing proppant-rock deformation upon experiencing proppant embedment are of crucial importance [39,61]. To date, many finite element models and continuum models have been developed to study grain crushing and embedment mechanisms [26,36,40,58].…”

Section: Introductionmentioning

confidence: 99%

Grain-scale analysis of proppant crushing and embedment using calibrated discrete element models

et al. 2022

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Proppant crushing and embedment in hydraulically-induced fractures is a major drawback to the recovery of unconventional oil/gas and geothermal energy production. This study provides a grain-scale analysis of the fracture evolution mechanisms of proppant crushing, rock fracture damage during proppant embedment, the influence of realistic reservoir/fracture fluid on proppant embedment, and the behaviour of proppant packs subjected to in-situ stresses using a discrete element modelling (DEM) approach. The results of this study reveal that the selection of an appropriate proppant type based on the nature of the reservoir formation plays a vital part in quantifying the degree of proppant crushing and embedment within fractures. The utilisation of frac-sand proppants instead of ceramic proppants in shallow soft sedimentary-based siltstone formations reduces proppant embedment up to 88%. However, whatever the depth of the fracture, the injection of ceramic proppants into granite-based geothermal formations is preferred to that of frac-sand proppants due to their lower proppant embedment and greater crush resistance. DEM analysis detected rock-spalling during the proppant embedment process, which ultimately led to the initiation of tensile-dominant secondary fractures in rocks. Fracture initiation, propagation, and coalescence during proppant crushing are analysed using calibrated DEM proppant-rock assemblies. Importantly, this study reveals that the saturation of formation rocks with fracturing/reservoir fluids may cause a significant increase in proppant embedment. Furthermore, proppant crushing, embedment, and re-arrangement mechanisms in proppant packs with different proppant distributions are analysed in this comprehensive numerical study.

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“…Based on experimental studies, Tan et al found that too small or too large fracturing fluid viscosity and injection rate are not conducive to the vertical extension of induced fractures and the improvement of reservoir stimulation volume (Tan et al, 2019). Based on laboratory experiments, Liu et al found that with the increase of fracturing fluid viscosity, formation fracture pressure and fracture propagation distance also increased (Liu et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

Research on the propagation mechanism of hydraulic fractures in infill horizontal wells

et al. 2022

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In recent years, infill horizontal well technology has been used to develop oil and gas in the remaining oil areas of unconventional low-permeability reservoirs. However, the initial fractures in parent wells will affect the hydraulic fractures formed by fracturing infilling horizontal wells. The interaction mechanisms between initial fractures and artificial fractures in infill horizontal wells are still unclear. Combined with the boundary element method and the maximum circumferential tensile stress criterion, a numerical model of hydraulic fracturing that can simulate the evolution of fracture trajectory and stress field was established. The analytical solution of the hydraulic fracture-induced stress field was used to verify the accuracy of the model. Using this model, propagation of hydraulic fractures in infill horizontal wells under different conditions was analyzed. Simulation results show that both the fracture spacing and well spacing have a significant impact on the propagation trajectory of hydraulic fractures in infill horizontal wells. The shorter the fracture spacing and well spacing is, the stronger the inter-fracture stress interference between the initial fractures and hydraulic fractures is. Reasonable fracture spacing and well spacing can enhance the induced stress field and form a complex fracture network in the reservoir. Too small well spacing may cause artificial fractures to communicate with initial fractures, thereby reducing hydraulic fracturing efficiency and limiting the stimulation volume of the reservoir.

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Experimental study on the effects of pre-cracks, fracturing fluid, and rock mechanical characteristics on directional hydraulic fracturing with axial pre-cracks

Cited by 27 publications

References 29 publications

Experimental Study on Optimization of Polymer Preslug Viscosity of ASP Flooding in Interlayer Heterogeneous Well Group Artificial Sandstone Core

Experimental Study on Optimization of Polymer Preslug Viscosity of ASP Flooding in Interlayer Heterogeneous Well Group Artificial Sandstone Core

Grain-scale analysis of proppant crushing and embedment using calibrated discrete element models

Research on the propagation mechanism of hydraulic fractures in infill horizontal wells

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