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Tadeusz W Patzek - One of the best experts on this subject based on the ideXlab platform.

  • Evaluation of production losses from unconventional shale reservoirs
    Journal of Natural Gas Science and Engineering, 2015
    Co-Authors: Umut Aybar, Mohammad O. Eshkalak, Kamy Sepehrnoori, Tadeusz W Patzek
    Abstract:

    The Promising production trends and predictions, as well as improvements in hydraulic fracturing and horizontal drilling technologies, have made unconventional reservoirs economically feasible. Although these reservoirs have high initial production rates, it is observed that their production performance declines fast. Therefore, it is necessary to identify the reasons behind the production performance reduction. With continuing production, pore pressure decreases and consequently the effective stress applying on Fractures increases. This phenomenon causes the Fracture closure. In this paper, both individual and combined effects of Natural Fracture and hydraulic Fracture closures on well performance are investigated. We use available experimental data to represent hydraulic and Natural Fracture conductivity alterations with changing stress conditions. Simulation results show that the individual effects of hydraulic and Natural Fracture closure on production performance is in the range of 6%e13% and 7%e23%, respectively. Additionally, the combined effect of Natural and hydraulic Fracture closure is in the range of 10%e25%. It is observed that the coupled effect of Natural and hydraulic Fracture conductivity losses is less than the summation of the individual effects. Sensitivity analysis is also performed for certain reservoir parameters. This work can provide a better understanding of the main reasons of production losses from unconventional reservoir simulations. © 2015 Elsevier B.V. All rights reserved.

  • the effect of Natural Fracture s closure on long term gas production from unconventional resources
    Journal of Natural Gas Science and Engineering, 2014
    Co-Authors: Umut Aybar, Mohammad O. Eshkalak, Kamy Sepehrnoori, Tadeusz W Patzek
    Abstract:

    Abstract The future U.S. and world energy supply is supported by the observed trends of long-term production forecasts from unconventional resources. Also, recent innovations in multi-pad horizontal drilling and hydraulic fracturing empower such trends to be economically viable. Nevertheless, the triggered Fractures in an unconventional reservoir rapidly shrink, as a result of produced gas that leads to a significant loss in long-term production. Hence, it is critical to quantify the effect of Fracture closure on long-term production for to reach an accurate production forecast. In this paper, the permeability changes of secondary Fractures network are investigated with respect to their effect on the long-term gas production from unconventional resources. An analytical trilinear model is revised and improved in order to handle the constant bottom-hole pressure production scenario and hence analyzing the cumulative gas production by considering the effect of stress on Natural Fracture permeability. In addition, a comprehensive sensitivity study is performed to rank the influence of uncertain parameters on cumulative production and consequently identify a condition in which a severe effect of pressure-dependent Natural Fracture on production is observed. It is concluded that the pressure-dependent Natural Fracture permeability can cause up to ten percent less cumulative production than considering the constant Natural Fracture permeability. Also, the improved analytical model is very fast and robust compared to the commercial numerical simulators. The advantage of this approach is to obtain a quick and accurate assessment of the complex production behavior of unconventional reservoirs. The findings of this paper provide valuable insights into long-term investment on unconventional reservoirs and guide decision making for the secondary or tertiary enhancement treatments of unconventional wells, such as re-fracturing.

Stephen E Laubach - One of the best experts on this subject based on the ideXlab platform.

  • Natural Fracture characterization in tight gas sandstones: Integrating mechanics and diagenesis
    AAPG Bulletin, 2009
    Co-Authors: Jon E Olson, Stephen E Laubach, R. H. Lander
    Abstract:

    Accurate predictions of Natural Fracture flow attributes in sandstones require an understanding of the underlying mechanisms responsible for Fracture growth and aperture preservation. Poroelastic stress calculations combined with Fracture mechanics criteria show that it is possible to sustain opening-mode Fracture growth with sublithostatic pore pressure without associated or preemptive shear failure. Crack-seal textures and Fracture aperture to length ratios suggest that preserved Fracture apertures reflect the loading state that caused propagation. This implies that, for quartz-rich sandstones, the synkinematic cement in the Fractures and in the rock mass props Fracture apertures open and reduces the possibility of aperture loss on unloading and relaxation. Fracture pattern development caused by subcritical Fracture growth for a limited range of strain histories is demonstrated to result in widely disparate Fracture pattern geometries. Substantial opening-mode growth can be generated by very small extensional strains (on the order of 10{â}ˆ'4); consequently, Fracture arrays are likely to form in the absence of larger scale structures. The effective permeabilities calculated for these low-strain Fracture patterns are considerable. To replicate the lower permeabilities that typify tight gas sandstones requires the superimposition of systematic cement filling that preferentially plugs Fracture tips and other narrower parts of the Fracture pattern.

  • a method to detect Natural Fracture strike in sandstones
    AAPG Bulletin, 1997
    Co-Authors: Stephen E Laubach
    Abstract:

    In siliciclastic hydrocarbon reservoir rocks, economic gas and oil production may depend on the attributes of Natural Fractures, and, with the advent of horizontal drilling, Fractures are increasingly exploration and development targets; yet reliable information on such key Fracture attributes as orientation (strike) is sparse because few Fractures intersect vertical well bores. This paper describes how Fracture strike can be documented on a bed-by-bed basis even in well bores where few or no visible Fractures are directly sampled. Quartz-lined opening-mode microFractures (lengths of microns to millimeters) in quartz-cemented sandstones commonly are not visible using standard petrographic methods, but systematic mapping of these microFractures is possible using photomultiplier-based electron beam-induced luminescence (scanned cathodoluminescence) imaging. As shown by observations, primarily from three Natural gas plays and one oil play in the United States, microFracture strike is a good guide to the strike of large Fractures (macroFractures) that formed concurrently. Because microFractures are widespread and small specimens can be used to get accurate Fracture-strike data, this approach can be applied to samples obtained from wireline-conveyed rotary (drilled) sidewall coring devices, as well as to samples from full-diameter core.

B. Lee - One of the best experts on this subject based on the ideXlab platform.

  • The Critical Role of In-Situ Pressure on Natural Fracture Shear and Hydraulic Fracturing-Induced Microseismicity Generation
    All Days, 2013
    Co-Authors: Fengshou Zhang, B. Lee, Neal Borden Nagel, Marisela Sanchez-nagel, Alireza Agharazi
    Abstract:

    Abstract In this work, the effect of in-situ pressure on Natural Fracture shear and hydraulic fracturing-induced microseismicity generation was evaluated using a discrete element model. Overall, the initial in-situ pressure was found to play a significant role in the ability to shear Natural Fractures during a hydraulic Fracture stimulation, largely through a reduction in the effective stresses acting on the Natural Fractures. Simply, the greater the initial in-situ pressure relative to the in-situ principal stresses, the greater the shear on Natural Fractures for a given stimulation treatment. Shear slip events on Natural Fractures were divided into "wet" events and "dry" events to help understand the shear failure mechanism and the induced-microseismicity complexity during the hydraulic fracturing process. The results showed that the density and distribution area of the slip events were affected by a combination of multiple factors. Dry events were mainly affected by the total stress change or shear stress change and the initial strength of the Natural Fractures while the wet events were affected by the total stress change or shear stress change, the initial strength of the Natural Fractures and the fluid leakoff area. The stimulated reservoir volume (SRV), measured by the scope of the wet events or the shape of the leakoff area, was affected by the trace of the hydraulic Fracture and the Fracture network connectivity in the matrix. These results provide further understanding and ability to interpret the different microseismicity responses seen in the field, which, ultimately, will allow for improved optimization of stimulation and completion strategies.

  • Coupled Numerical Evaluations of the Geomechanical Interactions Between a Hydraulic Fracture Stimulation and a Natural Fracture System in Shale Formations
    Rock Mechanics and Rock Engineering, 2013
    Co-Authors: N. B. Nagel, M. A. Sanchez-nagel, F. Zhang, X. Garcia, B. Lee
    Abstract:

    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.

Ahmad Ghassemi - One of the best experts on this subject based on the ideXlab platform.

  • Laboratory-Scale Investigation of the Slippage of a Natural Fracture Resulting from an Approaching Hydraulic Fracture
    Rock Mechanics and Rock Engineering, 2021
    Co-Authors: Ahmad Ghassemi
    Abstract:

    The interaction between a Natural Fracture (NF) and a hydraulic Fracture (HF) has been studied extensively, both experimentally and numerically, to better understand the potential for crossing and arrest of a hydraulic Fracture intersecting a Natural Fracture. However, the actual mechanical interaction between a hydraulic and a Natural Fracture or a bedding plane has not been studied, particularly under triaxial stress and injection conditions. Analysis of field microseismic data recorded during hydraulic fracturing shows that the bedding plane could slip due to the approaching hydraulic Fracture. In this paper, we present the results of some lab-scale experimental work, demonstrating HF/NF interaction with an emphasis on the slippage of a discontinuity surface. Injection pressure, stress applied, and the sample deformation are monitored during the tests. Acoustic Emission (AE) technology is employed to record the AE signals generated during Fracture initiation, propagation, and during the sliding of the joint. In addition, strain gauges are used to measure the slippage on the Natural Fracture. The tests are carried out on 101.6 mm diameter cylindrical samples of PMMA, shale, and granite. The calculated displacement based on the recorded strain clearly shows a jump at the breakdown point, which is accompanied by increased AE activity and stress drop. Analysis of the data clearly shows the occurrence of slippage on the joint in response to an approaching hydraulic Fracture. Expectedly, the degree of shear slip varies with Natural Fracture dip and friction angle.

  • Estimating Natural Fracture orientations using geomechanics based stochastic analysis of microseismicity related to reservoir stimulation
    Geothermics, 2019
    Co-Authors: Ahmad Ghassemi
    Abstract:

    Abstract Natural Fractures are the primary pathways for fluid migration and production in geothermal reservoirs. Reactivation (and possible propagation) of Natural Fractures is an important component of stimulation. Slip on these Natural Fractures induces Microseismicity (MEQs) and the locations of MEQ events reveal aspects of stimulation. This work first presents a Geomechanics-Based Stochastic Analysis of Microseismicity (GBSAM) to quantitatively estimate Natural Fracture orientations from MEQs recorded during reservoir stimulation. This is achieved by combining geomechanics and geostatistics to better constrain uncertainties in Natural Fracture orientations. The reservoir response to pore pressure changes is modeled using a finite duration line source to simulate water injection. The mechanism for generating MEQs is based on Mohr Coulomb failure criterion while allowing one Natural Fracture to generate multiple MEQs. Mahalanobis distance, a type of similarity measure technique, is then used to measure the similarity between the simulated MEQ distribution and the field-observed MEQ distribution to find the best Natural Fracture distribution that fits the field-observed MEQ data. The Natural Fracture orientations which correspond to best simulated MEQ distribution in GBSAM are considered to be a realistic realization of the subsurface conditions. As an application, the proposed GBSAM is applied to Newberry EGS, and Fenton Hill HDR stimulations to estimate the Natural Fracture orientations of these two systems. Results from GBSAM show that the Natural Fractures dip and dip direction inverted from field-observed MEQ distribution are in good agreement with the field results reported from borehole televiewer.

  • three dimensional poroelastic analysis of a pressurized Natural Fracture
    International Journal of Rock Mechanics and Mining Sciences, 2011
    Co-Authors: Xiaoxian Zhou, Ahmad Ghassemi
    Abstract:

    Abstract In this paper, a three-dimensional, fully coupled poroelastic, displacement discontinuity method is developed and used to analyze the temporal variation of slip, and opening of a Natural Fracture in response to its sudden pressurization. Numerical results show when a Fracture is pressurized at a level exceeding the normal in-situ stress, it increasingly opens with time as the rock evolves from an undrained state towards a drained state in accordance with the poroelastic theory. And, the pore pressure loading associated with pressurization of the Fracture faces induces a time-dependent Fracture closure related to rock dilation. The poroelastic analysis of a critically stressed Natural Fracture that is pressurized below the level required for jacking shows that the potential for Fracture failure and slip decreases with the passage of time in response to the pore pressure-induced increase of the normal stress on the joint.

  • Simulation of hydraulic Fracture propagation near a Natural Fracture using virtual multidimensional internal bonds
    International Journal for Numerical and Analytical Methods in Geomechanics, 2011
    Co-Authors: Z. Zhang, Ahmad Ghassemi
    Abstract:

    A virtual multidimensional internal bond (VMIB) model developed to simulate the propagation of hydraulic Fractures using the finite-element method is formulated within the framework of the virtual internal bond theory (VIB) that considers a solid as randomized material particles in the micro scale, and derives the macro constitutive relation from the cohesive law between the material particles with an implicit Fracture criterion. Hydraulic pressure is applied using a new scheme that enables simulation of hydraulically driven cracks. When the model is applied to study hydraulic Fracture propagation in the presence of a Natural Fracture, the results show the method to be very effective. It shows that although the in situ stress ratio is the dominant factor governing the propagation direction, a Natural fault can also strongly influence the hydraulic Fracture behavior. This influence is conditioned by the shear stiffness of the fault and the distance to the original hydraulic Fracture. The model results show that when the fault is strong in shear, its impact on hydraulic Fracture trajectory is weak and the hydraulic Fracture will likely penetrate the fault. For a weak fault, however, the Fracture tends to be arrested at the Natural fault. The distance between the fault and the hydraulic Fracture is also important; the fault influence increases with decreasing distance. The VMIB does not require selection of a Fracture criterion and remeshing when the Fracture propagates. Therefore, it is advantageous for modeling Fracture initiation and propagation in Naturally Fractured rock. Copyright © 2010 John Wiley & Sons, Ltd.

Yushi Zou - One of the best experts on this subject based on the ideXlab platform.

  • Numerical Investigation of Fracture Compressibility and Uncertainty on Water-Loss and Production Performance in Tight Oil Reservoirs
    Energies, 2019
    Co-Authors: Kai Liao, Shicheng Zhang, Yushi Zou
    Abstract:

    Multi-stage hydraulic fracturing along with horizontal wells are widely used to create complex Fracture networks in tight oil reservoirs. Analysis of field flowback data shows that most of the fracturing fluids are contained in a complex Fracture network, and Fracture-closure is the main driving mechanism during early clean up. At present, the related Fracture parameters cannot be accurately obtained, so it is necessary to study the impacts of Fracture compressibility and uncertainty on water-loss and the subsequent production performance. A series of mechanistic models are established by considering stress-dependent porosity and permeability. The impacts of Fracture uncertainties, such as Natural Fracture density, proppant distribution, and Natural Fracture heterogeneity on flowback and productivity are quantitatively assessed. Results indicate that considering Fracture closure during flowback can promote water imbibition into the matrix and delay the oil breakthrough time compared with ignoring Fracture closure. With the increase of Natural Fracture density, oil breakthrough time is advanced, and more water is retained underground. When Natural Fractures connected with hydraulic Fractures are propped, well productivity will be enhanced, but proppant embedment can cause a loss of oil production. Additionally, the Fracture network with more heterogeneity will lead to the lower flowback rate, which presents an insight in the role of Fractures in water-loss.