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Collaborating Authors
Hydraulic Fracturing
Abstract In this paper, the results of laboratory studies of hydraulic fracture in homogeneous sandstone blocks with man-made interfaces and heterogeneous shale blocks with weak natural interfaces are reported. Tests were conducted under similar stress conditions, with fluids of different viscosity and at different injection rates. The measurements and analysis allows the identification of fracture initiation and behavior. Fracturing with high viscosity fluids resulted in stable fracture propagation initiated before breakdown, while fracturing with low viscosity fluids resulted in unstable fracture propagation initiated almost simultaneously with breakdown. Analysis also allows us to measure the fluid volume entering the fracture and the fracture volume. Monitoring of Acoustic Emission (AE) hypocenter localizations, indicates the development of created fractured area including the intersection with interfaces, fluid propagation along interfaces, crossing interfaces, and approaching the boundaries of the block. We observe strong differences in hydraulic fracture behavior, fracture geometry and fracture propagation speed, when fracturing with water and high viscosity fluids. We also observed distinct differences between sandstone blocks and shale blocks, when a certain P-wave velocity ray path is intersected by the hydraulic fracture. The velocity increases in sandstones and decreases in shale.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.68)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.68)
- North America > United States > Wyoming > Laramie Basin > Niobrara Formation (0.99)
- North America > United States > Nebraska > Laramie Basin > Niobrara Formation (0.99)
- North America > United States > Kansas > Laramie Basin > Niobrara Formation (0.99)
- North America > United States > Colorado > Laramie Basin > Niobrara Formation (0.99)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.67)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (0.48)
- (2 more...)
Abstract We investigate the main pumping parameters that influence a fluid driven fracture in cohesive poroelastoplastic weak formation. These parameters include the fluid viscosity and the injection rate. The first parameter dominates in the mapping of the propagation regimes from toughness to viscosity while the second parameter controls the storage to leak-off dominated regime through diffusion. The fracture is driven in weak permeable formation by injecting an incompressible viscous fluid at the fracture inlet assuming plane strain conditions. Fluid flow in the fracture is modeled by lubrication theory. Irreversible rock deformation is modeled with the Mohr-Coulomb yield criterion assuming associative flow rule. Fracture propagation criterion is based on the cohesive zone approach. Leak-off is also considered. We perform numerical calculations with the finite element method to obtain the fracture opening, length and propagation pressure versus time. We demonstrate that pumping parameters influence the fracture geometry and fluid pressures in weak formations through the diffusion process that create back stresses and large plastic zones as the fracture propagates. We also show that the product of propagation velocity and fluid viscosity, (ยตv) that appears in the scaling controls the magnitude of the plastic zones and influences the net pressure and fracture geometry.
- Europe (0.68)
- North America > United States (0.46)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (0.90)
- Well Drilling > Pressure Management > Well control (0.72)
Abstract A rock mass is neither a continuous medium nor a totally discrete medium, it is a kind of defect material which contains many cracks, joints and faults. The nonlinear deformation behavior of a rock mass is induced by the propagation and coalescence of cracks and joints under external loads. Therefore, it is of important for rock engineering to analyze the propagation and coalescence process of cracks existed in a rock mass under external loads. The study of crack initiation and propagation is important for the understanding of rock mass behaviour which, in turn, affects rock engineering applications, such as tunnels, foundations and slopes, as well as hydrocarbon and geothermal energy extraction. Cracking mechanisms can be studied experimentally in the laboratory or in the field, or numerically. In the present study, distinct element method (DEM) which is capable to model various discontinuities was employed to simulate crack initiation and propagation in a rock masse specimen containing a single open and closed flaw. Initially, a rock domain containing a closed flaw was considered to model crack propagation. The analysis was performed by sequential modelling. Firstly, a model containing a single closed or open flaw was used to verify the types of propagation shown by Park and Bobet (2009). In these analyses, both open and closed flaws were considered and analysed with different spatial distribution (i.e. flaw angle). After results verification, the effect of open flaw filling material on crack propagation was analysed numerically. This characteristic has not yet been studied in crack propagation studies. The results obtained from open and closed flaws were in good agreement with experimental ones. All cracks mentioned in experimental literatures such as wing (tensile) cracks, coplanar secondary (shear) cracks and oblique secondary cracks were modelled successfully using DEM which indicates method capability to model nonlinear behaviour of rock masses subjected to external loadings. The emphasize of the study is to investigate the effects of open flaws containing filling material on crack initiation and propagation. Weak material was modelled as filling material. The results showed that when flaw is filled with weak materials (as it encountered frequently in natural rock masses) the cracking pattern is quite different with open flaws. In these occasions, the crack propagation direction is different. This phenomenon could be described in terms of stress attenuation in weak filling material, as stress concentration in filling materials causes change in crack propagation directions as well as crack length.
- Europe (0.46)
- Asia > Middle East > Israel > Mediterranean Sea (0.25)
- Well Completion > Hydraulic Fracturing (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.31)
Abstract The mechanics of fluid-driven fracture propagation through fracture networks is of central interest in gas and oil extraction procedures. A number of computational strategies have now been developed to simulate these processes although specific understanding of the propagation mechanics in the vicinity of pre-existing discontinuities or faults is still limited. This paper investigates the problem of formulating appropriate fluid branching logic at multiple flow path junctions and the influence of sudden contractions or expansions in the flow path channel width at discontinuity intersections. A plane strain model is assumed. A question of additional interest is the possible existence of a "fluid lag" region between the flow front and the mobilized fracture front. The paper explores some examples of flow propagation and branching through simple joint networks.
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (0.35)
Abstract Ability to induce complex, highly connected fracture networks, that can remain open during production, is the key to unlock permeability challenged shale gas plays. Within the time and pressure scale of hydraulic fracturing operations, it is difficult to create fracture complexity in ductile shales. However, when subjected to a high rate/pulse loading, rock might exhibit a brittle to ductile transition and a complex fracture network might be created. Along these lines, the concept of pulsed fracturing, that customizes the pressure-time behavior of a pulse source to create multiple fractures, is introduced. In this paper, an integrated 3D model that quantifies fracture initiation, growth, and coalescence due to initial and post-peak pulse loading is presented. The simulation involves a numerical algorithm that couples tensile/shear/compactive failure algorithms with dynamic fracture propagation and pore fluid pressure. Geomechanical modeling approach makes it possible to optimize pulsed fracturing for different shale plays. After constitutive model description and presentation of key aspects of the model, the model is employed to a reservoir dataset to evaluate pulsed fracturing as an alternative fracturing technique. The results show that, if designed accurately, pulsed fracturing could help trigger a ductile to brittle transition and can generate complex fracture networks.
- North America > United States > Texas (0.46)
- North America > United States > Colorado (0.28)
- North America > United States > West Virginia (0.28)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.93)
- Geology > Petroleum Play Type > Unconventional Play > Shale Play (0.68)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Shale gas (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (1.00)
Abstract We present a numerical model for the simultaneous initiation and subsequent propagation of multiple transverse hydraulic fractures from a horizontal wellbore. In particular, we investigate the efficiency and robustness of the multistage hydraulic fracturing technique. We restrict the created hydraulic fractures to remain radial and planar but fully account for the stress interaction between fractures, the fluid flow in the wellbore and across the different perforation clusters which are modeled via a classical relation between the friction pressure drop and the flow rate entering a given fracture. The initiation is modeled from a radial notch of given initial length using linear elastic fracture mechanics. The solver models the complete pressurization of the wellbore, the initiation of the different fractures and their propagation and interactions. The split of the fluid between the different clusters is part of the solution at each time-step. We present some validations and a case study investigating the effect of a number of heterogeneities (in-situ stress etc.) on the robustness of the limited entry technique.
- Well Drilling > Drilling Operations > Directional drilling (1.00)
- Well Completion > Hydraulic Fracturing (1.00)
- Well Completion > Completion Installation and Operations > Perforating (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
Abstract Dynamic loading methods promise new modes for stimulating geological resources, as the fracture patterns they produce can be tailored by the shape and nature of the pressure pulse employed. However, selecting the type of load is a difficult task: too slow and the stimulatory effect is reduced; too fast and the resource may be negatively impacted by wellbore damage, fines creation or permeability reduction. Moreover, modeling these systems proves challenging due to the myriad of length and timescales involved, combined with the need to accommodate both the generation of new fractures and propagation of preexisting fracture networks. GEODYN-L is a massively-parallel multi-material Lagrangian code that includes advanced contact models to simulate nonlinear wave propagation through heavily-jointed rock masses, along with material model libraries specifically developed to capture the dynamic response of geologic media. We present results using GEODYN-L to simulate dynamic stimulation of geologic resources with pre-existing fracture networks and discuss the implications of these results for enhancing fracture networks with dynamic loading techniques.
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.69)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (1.00)
- Reservoir Description and Dynamics > Non-Traditional Resources > Geothermal resources (1.00)
Abstract Hydraulic fracturing (HF) may lead to practical stress management possibilities by creating opportunities to control stress redistribution, or protecting locations where high stresses pose a threat to operations. These possibilities have application in petroleum engineering as well as mining. Understanding naturally fractured rock (NFR) behavior leads to better predictions of rock mass response to HF treatment and induced fracture initiation and propagation. Natural fractures exist in many different states, are reactivated by stress and pressure changes, and have alterable mechanical properties (e.g. stiffness, shear strength), leading to complex behavior in shear, opening, and closing reactions to stress changes. This article presents some attempts to understand and address simulation of HF interacting with a NFR using the Distinct Element Method (DEM) to represent the NFR. To this end, a coupled hydro-mechanical analysis is applied via the Universal Distinct Element Code (UDECโข) software to model both rock and fracture behavior in the HF/NFR system. In the current study, a Voronoi tessellated continuum has been generated to evaluate the effect of the stress ratio on flow into the joints by changing the differential principal compressive stresses. Given the difference in in situ stresses, pore pressure distribution is monitored and the distribution of slip and opening of fractures at different stress field anisotropy is investigated during pressurized hydraulic injection. Based on simulations, pore pressure decreases in a uniform pattern around the injection point in the isotropic stress state; however, the pressure distribution tends to become strongly anisotropic under a stronger differential stress. In addition, both normal and shear displacements show an increasing trend toward anisotropy under stronger stress differences. Applications may ensue with better understanding, such that HF strategies for strongly differential stress fields may evolve to be substantially different than for near-isotropic stress fields, and similar conclusions may ensue for random NFR fabrics, compared to cases with strongly oriented natural fracture fabric.
- North America > United States > Texas > Kleberg County (0.24)
- North America > United States > Texas > Chambers County (0.24)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
Abstract In this work, a hybrid discrete-continuum numerical model was used to simulate hydraulic fracture (HF) crossing and interaction with natural fractures or weakness planes. The model provided unique capabilities for investigating effects which have usually been overlooked or not able to be modeled in many of the previous studies on the subject. Multiple effects, such as the influence of stress conditions, material in-homogeneity (stiffness and strength contrast), natural fracture properties (crossing angle and friction angle), and injection parameters (injection rate and fluid viscosity) were investigated in this new work. Three types of intersection between an HF and orthogonally aligned natural fractures were identified by varying the coefficient of friction of the natural fractures and the stress ratio. In addition, the intersection angle between an HF and natural fractures or weakness planes was found to significantly affect the crossing. Decreasing the intersection angle with the natural fractures impeded direct crossing and favored the arrest of an HF. Material in-homogeneity and injection parameters were found to also greatly affect the HF crossing of natural fractures. Ultimately, the simulations showed that the geometry of an HF can be greatly affected by the interactions with adjacent natural fractures and weakness planes and that complex HF propagation patterns will occur due to complicated crossing behavior during hydraulic fracturing in naturally fractured reservoir systems.
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (1.00)
Abstract Robust and reliable hydraulic fracturing models that appropriately account for random initiation of fractures, strongly nonlinear coupling among deformation, fracturing and fluid flow in fracture apertures and leakage into porous rock matrix, would be a key step toward developing a better understanding of physics associated with hydraulic fracturing process. In this paper, we present a physics-based hydraulic fracturing simulator based on coupling a quasi-static discrete element model (DEM) for deformation and fracturing with conjugate lattice network flow model for fluid flow in both fractures and porous matrix. The coupled DEM-network flow model reproduces a variety of realistic growth patterns of hydraulic fractures. The effects of in situ stress, fluid viscosity, heterogeneity of rock mechanical properties and injection rate on the fracture patterns will be presented and discussed. In particular, simulation results of multistage horizontal wellbore with multiple perforations clearly demonstrate that elastic interactions among multiple propagating fractures, strong coupling between fluid pressure fluctuations within fractures and fracturing, and lower length scale heterogeneities, collectively lead to complicating fracturing patterns.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.51)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- (2 more...)