Itasca Houston Inc.

Itasca, United States

Itasca Houston Inc.

Itasca, United States
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Pettitt W.,Itasca Consulting Group Inc. | Pierce M.,Itasca Consulting Group Inc. | Damjanac B.,Itasca Consulting Group Inc. | Hazzard J.,Itasca Consulting Group Inc. | And 7 more authors.
Leading Edge (Tulsa, OK) | Year: 2011

Fracture network engineering (FNE) involves the design, analysis, modeling, and monitoring of infield activities aimed at enhancing or minimizing rock mass disturbance. FNE relies specifically on advanced techniques to model fractured rock masses and correlate microseismic (MS) field observations with simulated microseismicity generated from these models. Hydrofracture stimulation is an example where FNE is playing a role, with hydraulic treatments now being widely used to optimize production volumes and extraction rates in petroleum reservoirs, enhanced geothermal systems, and preconditioning operations in caving mines. MS monitoring is now becoming a standard tool for evaluating the geometry and evolution of the fracture network induced during a given treatment, principally by source locating MS hypocenters and visualizing these with respect to the treatment volume and infrastructure. The integrated use of synthetic rock mass (SRM) modeling of the hydrofracturing with enhanced microseismic analysis (EMA) within FNE provides a feedback loop in which SRM is enhanced and constrained by the information provided by the MS data. This improves interpretation via direct observation of the micromechanics within the distinct element models used. Recent developments in both SRM and EMA technologies are described using case studies of the techniques applied to hydrofracture stimulations. We identify and discuss some future developmental challenges these technologies face, including their further integration and validation so as to provide more efficient and robust application of the FNE approach. © 2011 Society of Exploration Geophysicists.


Li B.,Wenzhou University | Zhang F.,Itasca Houston Inc. | Gutierrez M.,Khalifa University | Gutierrez M.,Colorado School of Mines
Acta Geotechnica | Year: 2015

This paper presents results of three-dimensional simulations of the hollow cylindrical torsional shear test using the discrete element method. Three typical stress states that can be applied in the hollow cylindrical apparatus (HCA), i.e. triaxial, torsional compression and pure torsional, are examined in terms of the distributions of stresses and strains in the HCA sample. The initiation and propagation of the shear bands in the sample were characterized by porosity and shear strain rate distributions in the sample. The results show that the shear strain rate contour is a better indicator for shear band development than the porosity contours. It is demonstrated that the stresses and strains measured in the shear zone are significantly different from the boundary measurements and the average values used in HCA testing. Initially, the peak strength measured from the boundary forces was found to be slightly lower than that measured in the shear band. Subsequently, due to the formation of shear band, the stress ratio from boundary forces decreased significantly especially when the major principal stress is oriented 30° and 45° from the vertical. The evolutions of porosity, coordination number and particle rotation at different locations in the sample were also monitored. Finally, the appropriateness of the HCA is evaluated in comparison with previously published data. © 2014, Springer-Verlag Berlin Heidelberg.


Kallu R.R.,University of Nevada, Reno | Keffeler E.R.,RESPEC Consulting and Services | Watters R.J.,University of Nevada, Reno | Agharazi A.,Itasca Houston Inc.
International Journal of Mining Science and Technology | Year: 2015

Estimating weak rock mass modulus has historically proven difficult although this mechanical property is an important input to many types of geotechnical analyses. An empirical database of weak rock mass modulus with associated detailed geotechnical parameters was assembled from plate loading tests performed at underground mines in Nevada, the Bakhtiary Dam project, and Portugues Dam project. The database was used to assess the accuracy of published single-variate models and to develop a multivariate model for predicting in-situ weak rock mass modulus when limited geotechnical data are available. Only two of the published models were adequate for predicting modulus of weak rock masses over limited ranges of alteration intensities, and none of the models provided good estimates of modulus over a range of geotechnical properties. In light of this shortcoming, a multivariate model was developed from the weak rock mass modulus dataset, and the new model is exponential in form and has the following independent variables: (1) average block size or joint spacing, (2) field estimated rock strength, (3) discontinuity roughness, and (4) discontinuity infilling hardness. The multivariate model provided better estimates of modulus for both hard-blocky rock masses and intensely-altered rock masses. © 2015.


Han Y.,Itasca Consulting Group Inc. | Damjanac B.,Itasca Consulting Group Inc. | Nagel N.,Itasca Houston Inc.
46th US Rock Mechanics / Geomechanics Symposium 2012 | Year: 2012

In this paper, we present a microscopic numerical system for simulating the interaction between the natural fractures and hydraulic fracturing. In this system, the intact rock mass is represented by bonded particle model in Particle Flow Code (PFC); the pre-existing natural fractures are simulated by smooth-joint contact model; the fluid flow in the porous media and fracture and the buildup and dissipation of pore pressure are modeled by the pipe flow over the network connecting all the pores; and, the hydraulic fracturing is treated as dynamic mechanical and hydraulic pressure boundary or interior conditions along the hydraulic fractures. In our model, the hydro-mechanical response of the porous matrix, the fluid flow in the pore channels, the coupling of the matrix volumetric deformation and the pore fluid dissipation, and the reactivation and further development of natural fractures, are modeled naturally and realistically in a physically correct manner. After each component of the system is described in great details, an example is provided to illustrate the complete procedure of applying the developed system in solving practical problems. Copyright 2012 ARMA, American Rock Mechanics Association.


Nagel N.B.,Itasca Houston Inc. | Sanchez-Nagel M.,Itasca Houston Inc. | Lee B.,Itasca Houston Inc.
Society of Petroleum Engineers - SPE Hydraulic Fracturing Technology Conference 2012 | Year: 2012

Due to the low permeability of many shale gas reservoirs, multi-stage horizontal well completions are used to provide sufficient stimulated area to make an economic well. Furthermore, access to, and stimulation of, the natural fracture system is often critical to an economically successful well. During a given hydraulic fracture stimulation, the physical displacement of the fracture alters the stress field around it. Numerous authors have suggested that this altered stress field is beneficial to the stimulation of the natural fracture system; however, other authors have shown the potential to stabilize the natural fracture system - making it less likely to shear - due to the presence of a created hydraulic fracture. In this paper, we present the results of a detailed parametric evaluation of the shear failure (and, by analogy, the microseismicity) due to the creation of a hydraulic fracture as a function of fracture length within two different fracture networks (DFNs) using the 2D Distinct Element Model (DEM), UDEC. Simulations were conducted as a function of: 1) fracture strength; 2) DFN orientation within the stress field; 3) stress ratio (the ratio of the maximum horizontal stress to the minimum); 4) Poisson's ratio of the shale; and 5) Young's modulus of the shale. The results show the critical impact that changes in the hydraulic fracture length and the DFN orientation have on the shear of the natural fracture system. In contrast, the simulations suggest that stress ratio, Poisson's ratio, and Young's modulus have, at best, a second-order effect on the shearing - and likely the stimulation - of the natural fracture system. The results of the study provide a further, quantitative assessment of the critical parameters affecting shale gas completions and aid in the understanding and optimization of hydraulic fracture stimulations in very low permeability, naturally fractured reservoirs. Copyright 2012, Society of Petroleum Engineers.


Nagel N.B.,Itasca Houston Inc. | Sanchez-Nagel M.,Itasca Houston Inc.
Proceedings - SPE Annual Technical Conference and Exhibition | Year: 2011

In horizontal well shale completions, multiple stages, each often with multiple clusters, are used to provide sufficient stimulated area to make an economic well. Each created hydraulic fracture alters the stress field around it. When hydraulic fractures are placed close enough together, the well-known stress shadow effect occurs in which subsequent fractures are affected by the stress field from the previous fractures. The effects include higher net pressures, smaller fracture widths and changes in the associated complexity of the stimulation. The level of microseismicity is also altered by stress shadow effects. For example, it is commonly seen that the number of microseismic events is significantly reduced from the toe to the heal of the well, where the first frac stage is conducted at the toe of the well. In this paper, we present the results of a numerical evaluation of the effect of multiple hydraulic fractures on stress shadowing as a function of fracture spacing, shale rock mechanical properties, and the in-situ stress ratio. In addition, utilizing the inherent ability of discrete element models to evaluate shear and tensile failure along fracture surfaces, shear failure, as a proxy for microseismicity, is evaluated as a function of fracture-induced stress and stress shadowing. The results of the study provide a means to optimize shale completions by understanding the effect of stress ratio, rock mechanical parameters, and hydraulic fracture spacing on the stress shadow effect and the potential for changing fracture complexity. Copyright 2011, Society of Petroleum Engineers.


Zhang F.,Itasca Houston Inc. | Nagel N.,Itasca Houston Inc. | Sheibani F.,Itasca Houston Inc.
48th US Rock Mechanics / Geomechanics Symposium 2014 | Year: 2014

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. Copyright © 2014 ARMA, American Rock Mechanics Association.


Nagel N.B.,Itasca Houston Inc. | Sanchez-Nagel M.A.,Itasca Houston Inc. | Zhang F.,Itasca Houston Inc. | Garcia X.,Itasca Houston Inc. | Lee B.,Itasca Houston Inc.
Rock Mechanics and Rock Engineering | Year: 2013

Due to the low permeability of many shale reservoirs, multi-stage hydraulic fracturing in horizontal wells is used to increase the productive, stimulated reservoir volume. However, each created hydraulic fracture alters the stress field around it, and subsequent fractures are affected by the stress field from previous fractures. The results of a numerical evaluation of the effect of stress field changes (stress shadowing), as a function of natural fracture and geomechanical properties, are presented, including a detailed evaluation of natural fracture shear failure (and, by analogy, the generated microseismicity) due to a created hydraulic fracture. The numerical simulations were performed using continuum and discrete element modeling approaches in both mechanical-only and fully coupled, hydro-mechanical modes. The results show the critical impacts that the stress field changes from a created hydraulic fracture have on the shear of the natural fracture system, which in-turn, significantly affects the success of the hydraulic fracture stimulation. Furthermore, the results provide important insight into: the role of completion design (stage spacing) and operational parameters (rate, viscosity, etc.) on the possibility of enhancing the stimulation of the natural fracture network ('complexity'); the mechanisms that generate the microseismicity that occurs during a hydraulic fracture stimulation; and the interpretation of the generated microseismicity in relation to the volume of stimulated reservoir formation. © 2013 Springer-Verlag Wien.


Sheibani F.,Itasca Houston Inc. | Nagel N.,Itasca Houston Inc. | Zhang F.,Itasca Houston Inc.
48th US Rock Mechanics / Geomechanics Symposium 2014 | Year: 2014

Often, a key factor in the successful hydraulic fracture stimulation of unconventional reservoirs is the opening or shearing (and later extension) of natural fractures or weakness planes around a created hydraulic fracture. The behavior of natural fractures, or weakness planes, in response to hydraulic fracture stimulation can be complicated. Furthermore, the stimulation of these fractures and weakness planes is dependent on several critical, in-situ conditions that can increase (or decrease) the contribution of natural fractures and weakness planes to well production. The optimal economic completion, then, requires considering these factors during both stimulation design and post-stimulation evaluations. The simplistic, and traditional, assumption that hydraulic fractures are bi-wing, planar and symmetric around the weilbore has tended to bias the interpretation of different aspects of the stimulation process. However, hydraulic fracture monitoring methods, such as microseismicity, pressure evaluations, and the coring through of hydraulic fractures, have confirmed the complex nature of fracture propagation in unconventional plays, often due to the presence of natural fractures and weakness planes. Therefore, an improved consideration of natural fracture and weakness plane behavior during hydraulic fracturing will result in a better understanding of fluid treating pressures and hydraulic fracture geometry, which will help lead to more accurate estimations of production for unconventional plays. In this paper, the results of an extensive parametric study of in-situ stress conditions, in-situ pressure, natural fracture mechanical properties (cohesion and friction angle) and characteristics (joint orientation and initial aperture), and different operating conditions (single stage, simultaneous hydraulic fracture stages, and sequential hydraulic fracture stages) on injection (net) pressure behavior is presented. The results were generated using a 2-D distinct element model and capture the important role that, for example, initial natural fracture aperture and in-situ pressure play in the development of hydraulic fracture injection pressures in unconventional reservoirs. Copyright © 2014 ARMA, American Rock Mechanics Association.


Garcia X.,Itasca Houston Inc. | Nagel N.,Itasca Houston Inc. | Zhang F.,Itasca Houston Inc. | Sanchez-Nagel M.,Itasca Houston Inc. | Lee B.,Itasca Houston Inc.
47th US Rock Mechanics / Geomechanics Symposium 2013 | Year: 2013

In the oil and gas industry, vertical growth/containment of fractures during hydraulic fracturing is of pivotal importance to the success of well stimulations. Experimental work have improved our understanding of the topic, but it is sometimes difficult to explore, in isolation, some of the multiple parameters involved in the problem. Analytical models cannot account for the whole complexity of the problem, and although numerical models are an alternative, they also come with their own benefits and drawbacks. Oversimplification, limitations on the size of the treatable systems, and erroneous/doubtful assumptions are sometimes drawbacks of numerical approaches. In this work, an effort is made to overcome some of these issues and present a numerical model which incorporates the physics of fracture growth and does not rely on prescribed constitute laws or continuum equations. The approach is based on the discrete element method (DEM) and accounts for the physics of fracture growth from basic principles. The model has the benefit of being a hybrid model that includes the fine-details of tip mechanics plus the large-scale effects of an arbitrarily large surrounding medium. This approach was used to study, in isolation, the influence of toughness contrast on the propagation mode of a fracture through an interface separating two formations. The model captured the local scale effects of the interaction of the tip of a vertical fracture approaching a horizontal fracture while still being computationally efficient. The results obtained indicate that when varying the single parameter of toughness contrast, four main propagation modes were observed for Mode I fractures: straight crossing across the interface between layers, arrest at the interface, propagation across the interface but with a T-shaped fracture, and reinitiation of the fracture with an offset (jog). Copyright 2013 ARMA, American Rock Mechanics Association.

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