scholarly journals Steps to conducting a valid hydraulic-fracturing laboratory test

2013 ◽  
Vol 53 (1) ◽  
pp. 347 ◽  
Author(s):  
Mohammad Sarmadivaleh ◽  
Bahman Joodi ◽  
Amin Nabipour ◽  
Vamegh Rasouli
Keyword(s):  
Hydraulic Fracturing ◽  
Scaling Laws ◽  
Test Procedure ◽  
Fluid Viscosity ◽  
Pumping Rate ◽  
True Triaxial ◽  
Physical Experiments ◽  
Fracturing Process ◽  
Scale Down ◽  
Tight Formations

Several parameters are involved in a hydraulic-fracturing-operation, which is a technique used mainly in tight formations to enhance productivity. Formation properties, state of stresses in the field, injecting fluid characteristics, and pumping rate are among several parameters that can influence the process. Numerical analysis is conventionally run to simulate the hydraulic-fracturing process. Before operating the expensive fracturing job in the field, however, it would be useful to understand the effect of various parameters by conducting physical experiments in the lab. Laboratory experiments are also valuable for validating the numerical simulations. Applying the scaling laws, which are to correspond to the field operation with the test performed in the lab, are necessary to draw valid conclusions from the experiments. Dimensionless parameters are introduced through the scaling laws that are used to scale-down different parameters including the hole size, pump rate and fluid viscosity to that of the lab scale. Sample preparation and following a consistent and correct test procedure in the lab, however, are two other important factors that play a substantial role in obtaining valid results. The focus of this peer-reviewed paper is to address the latter aspect; however, a review of different scaling laws proposed and used will be given. The results presented in this study are the lab tests conducted using a true triaxial stress cell (TTSC), which allows simulation of hydraulic-fracturing under true field stress conditions where three independent stresses are applied to a cubic rock sample.

scholarly journals A criterion for identifying a mixed-mode I/II hydraulic fracture crossing a natural fracture in the subsurface

2020 ◽  
Vol 38 (6) ◽  
pp. 2507-2520
Author(s):  
Yijin Zeng ◽  
Wan Cheng ◽  
Xu Zhang ◽  
Bo Xiao
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Mixed Mode ◽  
Petroleum Reservoirs ◽  
In Situ Stress ◽  
Natural Fracture ◽  
Mode I ◽  
Pure Mode ◽  
True Triaxial ◽  
Fracturing Process

Hydraulic fracturing has been proven to be an effective technique for stimulating petroleum reservoirs. During the hydraulic fracturing process, the effects of the natural fracture, perforation orientation, stress reorientation, etc. lead to the production of a non-planar, mixed-mode I/II hydraulic fracture. In this paper, a criterion for a mixed-mode I/II hydraulic fracture crossing a natural fracture was first proposed based on the stress field around the hydraulic and natural fractures. When the compound degree (KII/KI) approaches zero, this criterion can be simplified to identify a pure mode I hydraulic fracture crossing a natural fracture. A series of true triaxial fracturing tests were conducted to investigate the influences of natural fracture occurrence and in situ stress on hydraulic fracture propagation. These experimental results agree with the predictions of the proposed criterion.

scholarly journals Numerical Simulation Study on Propagation of Initial Microcracks in Cement Sheath Body during Hydraulic Fracturing Process

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1260
Author(s):  
Yuqiang Xu ◽  
Yan Yan ◽  
Shenqi Xu ◽  
Zhichuan Guan
Keyword(s):  
Elastic Modulus ◽  
Hydraulic Fracturing ◽  
Internal Pressure ◽  
Element Model ◽  
Fluid Viscosity ◽  
Fracturing Fluid ◽  
Zone Method ◽  
Geological Conditions ◽  
Fracturing Process ◽  
Cement Sheath

Microcracks caused by perforating operations in a cement sheath body and interface have the potential to further expand or even cause crossflow during hydraulic fracturing. Currently, there are few quantitative studies on the propagation of initial cement-body microcracks. In this paper, a three-dimensional finite element model for the propagation of initial microcracks of the cement sheath body along the axial and circumferential directions during hydraulic fracturing was proposed based on the combination of coupling method of fluid–solid in porous media and the Cohesive Zone Method. The influence of reservoir geological conditions, the mechanical properties of a casing-cement sheath-formation system, and fracturing constructions in the propagation of initial axial microcracks of a cement sheath body was quantitatively analyzed. It can be concluded that the axial extension length of microcracks increased with the increase of elastic modulus of the cement sheath and formation, the flow rate of fracturing fluid, and casing internal pressure, and decreased with the increase of the cement sheath tensile strength and ground stress. The elastic modulus of the cement sheath had a greater influence on the expansion of axial cracks than the formation elastic modulus and casing internal pressure. The effect of fracturing fluid viscosity on the crack expansion was negligible. In order to effectively slow the expansion of the cement sheath body crack, the elastic modulus of the cement sheath can be appropriately reduced to enhance its toughness under the premise of ensuring sufficient strength of the cement sheath.

scholarly journals Fracture Propagation and Morphology Due to Non-Aqueous Fracturing: Competing Roles between Fluid Characteristics and In Situ Stress State

Minerals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 428
Author(s):  
Yunzhong Jia ◽  
Zhaohui Lu ◽  
Hong Liu ◽  
Jiehao Wang ◽  
Yugang Cheng ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Hydraulic Fracturing ◽  
Fracture Propagation ◽  
Horizontal Stress ◽  
In Situ Stress ◽  
Fluid Viscosity ◽  
Low Viscosity ◽  
Fracturing Process ◽  
Fluid Characteristics

Non-aqueous or gaseous stimulants are alternative working fluids to water for hydraulic fracturing in shale reservoirs, which offer advantages including conserving water, avoiding clay swelling and decreasing formation damage. Hence, it is crucial to understand fluid-driven fracture propagation and morphology in shale formations. In this research, we conduct fracturing experiments on shale samples with water, liquid carbon dioxide, and supercritical carbon dioxide to explore the effect of fluid characteristics and in situ stress on fracture propagation and morphology. Moreover, a numerical model that couples rock property heterogeneity, micro-scale damage and fluid flow was built to compare with experimental observations. Our results indicate that the competing roles between fluid viscosity and in situ stress determine fluid-driven fracture propagation and morphology during the fracturing process. From the macroscopic aspect, fluid-driven fractures propagate to the direction of maximum horizontal stress direction. From the microscopic aspect, low viscosity fluid easily penetrates into pore throats and creates branches and secondary fractures, which may deflect the main fracture and eventually form the fracture networks. Our results provide a new understanding of fluid-driven fracture propagation, which is beneficial to fracturing fluid selection and fracturing strategy optimization for shale gas hydraulic fracturing operations.

scholarly journals The Role of Rock Matrix Permeability in Controlling Hydraulic Fracturing in Sandstones

2021 ◽  
Author(s):  
Marco Fazio ◽  
Peter Ibemesi ◽  
Philip Benson ◽  
Diego Bedoya-González ◽  
Martin Sauter
Keyword(s):  
Hydraulic Fracturing ◽  
Pore Space ◽  
Hydraulic Fractures ◽  
Low Permeability ◽  
Fluid Viscosity ◽  
Rock Matrix ◽  
Porous Rock ◽  
Sleeve Fracture ◽  
Matrix Permeability ◽  
Fracturing Process

AbstractA concomitant effect of a hydraulic fracturing experimenting is frequently fluid permeation into the rock matrix, with the injected fluid permeating through the porous rock matrix (leak-off) rather than contributing to the buildup of borehole pressure, thereby slowing down or impeding the hydro-fracturing process. Different parameters, such as low fluid viscosity, low injection rate and high rock permeability, contribute to fluid permeation. This effect is particularly prominent in highly permeable materials, therefore, making sleeve fracturing tests (where an internal jacket separates the injected fluid in the borehole from the porous rock matrix) necessary to generate hydraulic fractures. The side effect, however, is an increase in pressure breakdown, which results in higher volume of injected fluid and in higher seismic activity. To better understand this phenomenon, we report data from a new comparative study from a suite of micro-hydraulic fracturing experiments on highly permeable and on low-permeability rock samples. Experiments were conducted in both sleeve fracture and direct fluid fracture modes using two different injection rates. Consistent with previous studies, our results show that hydraulic fracturing occurred only with low permeation, either due to the intrinsic low permeability or due to the presence of an inner silicon rubber sleeve. In particular, due to the presence of quasi-impermeable inner sleeve or borehole skin in the sleeve fracturing experiment, fracturing occurs, with the breakdown pressure supporting the linear elastic approach considering poroelastic effects, therefore, with low stress drop and consequently low microseismicity. Rock matrix permeability also controls the presence of precursory Acoustic Emission activity, as this is linked to the infiltration of fluids and consequent expansion of the pore space. Finally, permeability is shown to mainly control fracturing speed, because the permeation of fluid into the newly created fracture via the highly permeable rock matrix slows down its full development. The application of these results to the field may help to reduce induced seismicity and to conduct well stimulation in a more efficient way.

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