Browsing by Subject "fracture"
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Item A Global Model for Fracture Falloff Analysis(2014-10-29) Marongiu-Porcu, MatteoThe reservoir permeability is an essential input for the optimum design of modern hydraulic fracture treatments, which are undeniably the crucial technology involved in the development of tight and/or unconventional gas reservoirs. The fracture geometry and pumping execution, as well as the well architecture, can be designed to maximize the well productivity, provided the reservoir permeability is known, but in tight formations estimation of permeability and pressure can be impractical or even impossible to determine by conventional pressure buildup transient tests because no flow will occur without hydraulic fracture stimulation. Various authors have shown how fracture calibration tests, intended for the final fracture treatment calibration (i.e. estimation of closure stress, leakoff coefficient and fracture fluid efficiency) can be used to estimate reservoir permeability as well. However, all the proposed techniques depend on specialized plots that are designed to show a straight line for a portion of the data, from which parameters are determined either from the slope of the line or from its endpoints, and there is a risk that apparent straight lines may lead to erroneous results, particularly when the absence of late time pseudo-radial flow data is ignored or not recognized. This dissertation introduces a new global model for the before-closure and after-closure analysis of the pressure falloff following a step-rate or constant rate fracture calibration test, using a single log-log diagnostic plot, as common practice within the pressure transient analysis literature. This model provides a complete assessment tool that allows quantification of all fracture parameters (closure stress, closure time, fracture fluid efficiency, leakoff coefficient and estimate of the induced fracture geometry) as well as reservoir permeability and formation pressure, provided that enough time is allowed for the falloff to reach pseudo-radial flow regime. Both oil and gas reservoirs can be effectively studied. Another major advantage provided by this approach is that this model can be used to optimize a priori the design of the fracture calibration test that would allow determination of all the involved parameters, including reservoir permeability. Field data will be used to validate the model and demonstrate its added value over current interpretation methods.Item Brittle Fracture Modeling with a Surface Tension Excess Property(2012-10-30) Ferguson, LaurenThe classical theory of linear elastic fracture mechanics for a quasi-static crack in an infinite linear elastic body has two significant mathematical inconsistencies: it predicts unbounded crack-tip stresses and an elliptical crack opening profile. A new theory of fracture developed by Sendova and Walton, based on extending continuum mechanics to the nanoscale, corrects these erroneous effects. The fundamental attribute of this theory is the use of a dividing surface to describe the material interface. The dividing surface is endowed with an excess property, namely surface tension, which accounts for atomistic effects in the interfacial region. When the surface tension is taken to be a constant, Sendova and Walton show that the theory reduces the crack-tip stress from a square root to a logarithmic singularity and yields a finite angle opening profile. In addition, they show that if the surface tension depends on curvature, the theory completely removes the stress singularity at the crack-tip, for all but countably many values of the two surface tension parameters, and yields a cusp-like opening profile. In this work, we develop a numerical model using the finite element method for the Sendova-Walton fracture theory applied to the classical Griffith crack problem in the case of constant surface tension. We show that the numerical model behaves as predicted by the theory, yielding a reduced crack-tip singularity and a finite opening angle for all nonzero values of the constant surface tension. We also lay the groundwork for the numerical implementation of the curvature-dependent model by constructing an algorithm to determine the appropriate threshold values for the surface tension parameters that guarantee bounded crack-tip stresses. These values can then be directly applied to the forthcoming numerical model.Item Evaluation of acid fracturing based on the "acid fracture number" concept(Texas A&M University, 2006-08-16) Alghamdi, AbdulwahabAcid fracturing is one of the preferred methods to stimulate wells in carbonate reservoirs. It consists of injecting an acid solution at high enough pressure to break down the formation and to propagate a two-wing crack away from the wellbore. The acid reacts with the carbonate formation and this causes the etching of the fracture surfaces. After the treatment, the created etched surfaces do not close perfectly and that leaves behind a highly conductive path for the hydrocarbons to be produced. We distinguish the issue of treatment sizing (that is the determination of the volume of acid to be injected) and the issue of creating optimum fracture dimensions given the size of the treatment. This is reasonable because the final cost of a treatment is determined mainly by the volume of acid injected and our goal should be to achieve the best performance of the treated well. The well performance depends on the created fracture dimensions and fracture conductivity and might change with time due to various reasons. This research evaluates two field cases from Saudi Aramco where acid fracturing treatment has been used to stimulate a carbonate formation. I investigated the following issues: a) how effective was the treatment to restoring the initial productivity, b) how did the productivity of the well change with time; c) what are the possible reasons for the change in performance, d) what are our options to improve acid fracture design in the future? Based on our research work both near-well liquid drop-out and fractureconductivity deterioration can impact the production in different proportion. Moreover, the fracturing model tends to overestimate the fracture conductivity in some cases as shown in SA-2. Also, the ??Acid fracture Number?? concept proves to be an effective way to evaluate the acid fracturing treatment. Several recommendations were made based on this research work as described in the last part of my thesis.Item Experimental analysis of the extension to shear fracture transition in Berea Sandstone(Texas A&M University, 2005-11-01) Bobich, Jennifer KayTo characterize low-pressure, brittle deformation in porous, granular rock, notchcut cylinders (30 mm neck diameter) of Berea Sandstone were extended in a triaxial apparatus from 10 to 160 MPa confining pressure at strain rates of 10-4 s-1 and 10-5 s-1. Acoustic emission counts were monitored when extending samples at a slow strain rate. Stress at fracture is characterized by the least compressive principal stress, ??3, and maximum compressive principal stress, ??1 (??1 = Pc). A change in strength dependence on pressure at Pc = 50 MPa corresponds to a change from pure macroscopic extension fracture to mixed-mode opening and shear fracture, and likely reflects the increase in mean stress that suppresses the propagation of extension fractures and the interaction between closely-spaced stepped cracks. Within the extension fracture regime (Pc < 50 MPa), ??3 at failure becomes slightly more tensile with an increase in Pc. At Pc > 50 MPa, ??3 at failure becomes more compressive with an increase in Pc and follows Coulomb behavior; however, the angle between the fracture surface and ??1 increases continuously with Pc. Fracture surfaces characteristic of the extension to shear fracture transition appear as linked, stepped extension fractures; the length of extensional segments decreases with increasing pressure. The onset of acoustic emissions and inelastic strain at fracture occurs at earlier points in the strain history with pressure, consistent with the Griffith prediction of the beginning of fracture growth.Item Feasibility of the Interferometric Neighboring Fracture Method and Improved Relative Travel Time Measurement(2014-12-16) Shtaygrud, IlaanThe recently proposed Interferometric Neighboring Fracture (INF) localization method places unique and demanding constraints on relative travel time measurement accuracy and precision, while sampling a function of relative travel times between pairs of microseismic events as measured along a linear array. Conducting two synthetic trials, I analyze the relationship between event-receiver geometry and relative travel time measurement error and its effect on the feasibility of INF localization. The results indicate that even for typical hydraulic fracturing monitoring geometries, measurement error can exceed the feasible error limits of INF localization. In order to mitigate this error, I propose a new relative travel time measurement technique, Modified Adaptive Steering (MAS), along with a unique preprocessing methodology, Progressive Template Extraction (PTE). Analyzing synthetic data sets with varying SNR ratios, and a field recorded microseismic data set, I compare the performance of PTE-preprocessed MAS to conventional cross-correlation (CXC). Results of both synthetic and field recorded data analysis indicate that PTE enhanced MAS outperforms CXC as a general lag measurement technique, reducing average lag error by as much as 1.25 ms at SNRs below 10. With respect to the unique constraints of the INF method, PTE-MAS produces as many as 4.2 times as many usable samplings of the relative travel time function, while reducing error in stationary position and lag by up to 15 m and 2.5 ms, respectively.Item Fracture characterization and estimation of fracture porosity of naturally fractured reservoirs with no matrix porosity using stochastic fractal models(2009-05-15) Kim, Tae HyungDetermining fracture characteristics at the laboratory scale is a major challenge. It is known that fracture characteristics are scale dependent; as such, the minimum sample size should be deduced in order to scale to reservoir dimensions. The main factor affecting mechanical and hydrological characteristics of natural fractures is aperture distribution, which is a function of scale and confining pressure, rather than roughness of one fracture surface. Scale and pressure dependencies of artificial and natural fractures were investigated in this study using an X-Ray CT Scanner. Fractal dimension, D, and amplitude parameter, A, of fracture aperture approaches a constant value with increased sampling area, similar to the behavior of fracture roughness. In addition, both parameters differ under different confining pressures for a reference sampling area. Mechanical properties of fracture-fracture deformation behavior and fracture normal stiffness were obtained from CT scan data as well. Matrix porosity is relatively easy to measure and estimate compared to fracture porosity. On the other hand, fracture porosity is highly heterogeneous and very difficult to measure and estimate. When matrix porosity of naturally fractured reservoirs (NFR) is negligible, it is very important to know fracture porosity to evaluate reservoir performance. Since fracture porosity is highly uncertain, fractal discrete fractal network (FDFN) generation codes were developed to estimate fracture porosity. To reflect scale dependent characteristics of fracture networks, fractal theories are adopted. FDFN modeling technique enables the systematic use of data obtained from image log and core analysis for estimating fracture porosity. As a result, each fracture has its own fracture aperture distribution, so that generated FDFN are similar to actual fracture systems. The results of this research will contribute to properly evaluating the fracture porosity of NFR where matrix porosity is negligible.Item Interpretation, Analysis and Design of Inter-well Tracer Tests in Naturally Fractured Reservoirs(2013-08-19) Alramadhan, Aymen AbduljalilIn order to understand the complex fracture network that controls water movement in Sherrod Area of Spraberry Field in West Texas and to better manage the on-going waterflood performance, a field scale inter-well tracer test was implemented. This test presents the largest inter-well tracer test in naturally fractured reservoirs reported in the industry and includes the injection of 13 different tracers and sampling of 110 producers in an area covering 6533 acres. Sherrod tracer test generated a total of 598 tracer responses from 51 out of the 110 sampled producers. Tracer responses showed a wide range of velocities from 14 ft/day to ultra-high velocities exceeding 10,000 ft/day with same-day tracer breakthrough. Re-injection of produced water has caused the tracers to be re-injected and added an additional challenge to diagnose and distinguish tracer responses affected by water recycling. Historical performance of the field showed simultaneous water breakthrough of a large number of wells covering entire Sherrod area. This research investigate analytical, numerical, and inversion modeling approaches in order to categorize, history match, and connect tracer responses with water-cut responses with the objective to construct multiple fracture realizations based entirely on water-cut and tracers? profiles. In addition, the research highlight best practices in the design of inter-well tracer tests in naturally fractured reservoirs through lessons learned from Sherrod Area. The large number of tracer responses from Sherrod case presents a case of naturally fractured reservoir characterization entirely based on dynamic data. Results indicates that tracer responses could be categorized based on statistical analysis of tracer recoveries of all pairs of injectors and producers with each category showing distinguishing behavior in tracers? movement and breakthrough time. In addition, it showed that tracer and water-cut responses in the field are dominantly controlled by the fracture system revealing minimum information about the matrix system. Numerical simulation studies showed limitation in dual porosity formulation/solvers to model tracer velocities exceeding 2200 ft/day. Inversion modeling using Gradzone Analysis showed that east and north-west of Sherrod have significantly lower pore volume compared to south-west.Item Laboratory Evaluation of Hot-Mix Asphalt Concrete Fatigue Cracking Resistance(2012-02-14) Jamison, Brandon ParkerThe recent changes in the Texas Department of Transportation (TxDOT) hot mix asphalt (HMA) mix design procedures to ensure that the mixture types routinely used on Texas highways are not prone to rutting raised concerns that these mixture types are now more susceptible to fatigue cracking. The primary goal of this study was to evaluate fatigue cracking test methods and recommend that which is both simple and robust, especially in qualifying commonly used Texas mixture types. One way to minimize fatigue cracking is through material screening and selection of appropriate mix designs that are representative of fatigue-resistant HMA mixes. However, there are not many standardized laboratory fracture resistance tests that have been universally adopted for routine mix design and/or screening purposes for HMA fatigue resistance. In this study, four different fracture test methods: the Overlay Tester (OT), Direct Tension (DT), Indirect Tension (IDT), and Semicircular Bending (SCB) tests were comparatively evaluated for their potential application as surrogate tests for routine fracture resistance evaluation and screening of HMA mixes in the laboratory. The evaluation criteria included: rationality of the test concept and correlation to field performance, repeatability and variability, simplicity and practicality of the sample fabrication process, and simplicity of data analysis. Results and key findings based on the laboratory fatigue resistance characterization of various commonly used Texas coarse- and fine-graded HMA mixes (Type B, C, and D) are presented in this paper. Overall, preliminary findings indicated that no monotonically-loaded test would be appropriate as a surrogate fatigue resistance test; however, the SCB test showed potential as a repeated-loading test. Suggested SCB test improvements include developing the repeated SCB test protocol, determining the appropriate failure criterion, and correlating laboratory performance to field performance.Item Modeling fluid flow through single fracture using experimental, stochastic, and simulation approaches(Texas A&M University, 2004-09-30) Alfred, DicmanThis research presents an approach to accurately simulate flow experiments through a fractured core using experimental, stochastic, and simulation techniques. Very often, a fracture is assumed as a set of smooth parallel plates separated by a constant width. However, the flow characteristics of an actual fracture surface are quite different, affected by tortuosity and the impact of surface roughness. Though several researchers have discussed the effect of friction on flow reduction, their efforts lack corroboration from experimental data and have not converged to form a unified methodology for studying flow on a rough fracture surface. In this study, an integrated methodology involving experimental, stochastic, and numerical simulations that incorporate the fracture roughness and the friction factor is shown to describe flow through single fractures more efficiently. Laboratory experiments were performed to support the study in quantifying the flow contributions from the matrix and the fracture. The results were used to modify the cubic law through reservoir simulations. Observations suggest that the fracture apertures need to be distributed to accurately model the experimental results. The methodology successfully modeled fractured core experiments, which were earlier not possible using the parallel plate approach. A gravity drainage experiment using an X-ray CT scan of a fractured core has also validated the methodology.Item Physical Simulation of an Embedded Surface Mesh Involving Deformation and Fracture(2012-07-16) Clack, BillySimulating virtual objects which can deform or break apart within their environments is now common in state-of-the-art virtual simulations such as video games or surgery simulations. Real-time performance requires a physical model which provides an approximation to the true solution for fast computations but at the same time provides enough believability of the simulation to the user. Recent research in object deformation and fracture has revolved around embedding portions of the simulation for graphical display inside a much simpler physical domain which is invisible to the user. Embedding complex geometry in a simpler domain allows for very complex effects to occur in a much more robust and computationally efficient manner. This thesis explores a novel method to efficiently embed a high-resolution surface mesh inside a coarse tetrahedral physical mesh for the purposes of interactive simulation and display. A technique to display interior regions as solid geometry without explicitly re-meshing the graphical mesh during fracture has been explored and developed. Keeping the graphical mesh static in memory during simulation allows the geometry to be off-loaded to the GPU while shaders can be utilized to only display portions of the geometry which are locally contained within the physical mesh. Recent advances in GPU technology have also been exploited in order to provide an increase in visual fidelity and help achieve the illusion that the virtual object itself is breaking apart in a physically plausible manner.Item Role of Family Satisfaction in Predicting Life Satisfaction Trajectories Over the First Five Years Following Acquired Disability(2012-10-19) Herna?ndez, Caitlin LouiseThis study aimed to model the trajectories of life satisfaction as influenced by functional impairment and family satisfaction over a five-year period following spinal cord injury, severe burns, and lower-extremity fractures. Marital status and injury type were included to estimate predicted life satisfaction over the five-year period post-injury. Measures: Six-hundred sixty-two participants completed the Functional Independence Measure, Family Satisfaction Scale, and Life Satisfaction Inventory at 12, 24, 48, and 60 months post-injury. Results: Family satisfaction was a consistent predictor of life satisfaction across models. Consistent with past research (Resch et al., 2009), functional impairment was significantly predictive of life satisfaction. Conclusions: Individuals predicted to be most at risk were those individuals with severe burns, who were divorced or separated, with low family satisfaction, and/or high functional impairment.Item Strategies to reduce terminal water consumption of hydraulic fracture stimulation in the Barnett Shale(2009-08) Harold, Jennifer Marie Secor; Groat, Charles G.; Schuster, Stefan K.; Fialkoff, Jason S.Horizontal drilling and hydraulic fracture stimulation have enabled the economic development of unconventional resource plays. An average horizontal well in the Barnett Shale requires 3 to 4 million gallons of fresh water, 90% of which is used for hydraulic fracture stimulation. While the water consumption of Barnett Shale operations is less than 1% of total Region C consumption, extended drought conditions and competing demands for water resources are placing pressure on operators to reduce terminal water consumption. Strategies which reduce water requirements associated hydraulic fracture stimulation without compromising the efficiency and cost of energy production are essential in developing a comprehensive policy on energy-water management. Recycling and reuse technologies were evaluated on the basis of performance, cost, and capacity to treat reclaimed flowback water and oilfield brine. Recycling flowback fluids for future hydraulic fracture applications is the most practical repurposing of oilfield waste. The low TDS content of flowback derived from water-based fracs permits multiple treatment options. Mobile thermal distillation technology has emerged as the prevailing technique for recycling flowback water, yielding maximum water savings and reduced operating costs. The estimated cost of recycling flowback water by thermal distillation is $3.35/bbl. Compared to the current cost of disposal, recycling provides an opportunity to minimize waste and reduce the fresh water requirements of hydraulic fracture stimulation at an incremental cost. The stewardship role of the Texas Legislature is to protect the water resources of the state and to facilitate the Regional Water Planning Process, ensuring future water needs are met. The support and participation of the Legislature and other planning entities is critical in advancing the energy-water nexus. As operators pursue innovative water management practices to reduce terminal water consumption in the oilfield, the Barnett Shale positions itself as a model for sustainable water use in the development of unconventional shale resources. The cost of recycling and reuse technology limits the participation of small and mid-size operators who possess the greatest market share of the Barnett Shale. Funding for research and implementation of water-conscious strategies such as shared recycling facilities, CO2 capture and storage, and pipeline infrastructure would create multi-user opportunities to promote conservation and reduce net consumption of fresh water supplies. Through the integration of technology and policy, terminal water consumption in the Barnett Shale can be greatly diminished.Item The Asperity-deformation Model Improvements and Its Applications to Velocity Inversion(2010-01-16) Bui, Hoa Q.Quantifying the influence of pressure on the effective elastic rock properties is important for applications in rock physics and reservoir characterization. Here I investigate the relationship between effective pressure and seismic velocities by performing inversion on the laboratory-measured data from a suite of clastic, carbonate and igneous rocks, using different analytic and discrete inversion schemes. I explore the utility of a physical model that models a natural fracture as supported by asperities of varying heights, when an effective pressure deforms the tallest asperities, bringing the shorter ones into contact while increasing the overall fracture stiffness. Thus, the model is known as the ?asperity-deformation? (ADM) or ?bed-of-nails? (BNM) model. Existing analytic solutions include one that assumes the host rock is infinitely more rigid than the fractures, and one that takes the host-rock compliance into account. Inversion results indicate that although both solutions can fit the data to within first-order approximation, some systematic misfits exist as a result of using the rigid-host solution, whereas compliant-host inversion returns smaller and random misfits, yet out-of-range parameter estimates. These problems indicate the effects of nonlinear elastic deformation whose degree varies from rock to rock. Consequently, I extend the model to allow for the pressure dependence of the host rock, thereby physically interpreting the nonlinear behaviors of deformation. Furthermore, I apply a discrete grid-search inversion scheme that generalizes the distribution of asperity heights, thus accurately reproduces velocity profiles, significantly improves the fit and helps to visualize the distribution of asperities. I compare the analytic and numerical asperity-deformation models with the existing physical model of elliptical ?pennyshape? cracks with a pore-aspect-ratio (PAR) spectrum in terms of physical meaning and data-fitting ability. The comparison results provide a link and demonstrate the consistency between the use of the two physical models, making a better understanding of the microstructure as well as the contact mechanism and physical behaviors of rocks under pressure. ADM-based solutions, therefore, have the potential to facilitate modeling and interpretation of applications such as time-lapse seismic investigations of fractured reservoirs.Item The Effect of Proppant Size and Concentration on Hydraulic Fracture Conductivity in Shale Reservoirs(2013-04-11) Kamenov, AntonHydraulic fracture conductivity in ultra-low permeability shale reservoirs is directly related to well productivity. The main goal of hydraulic fracturing in shale formations is to create a network of conductive pathways in the rock which increase the surface area of the formation that is connected to the wellbore. These highly conductive fractures significantly increase the production rates of petroleum fluids. During the process of hydraulic fracturing proppant is pumped and distributed in the fractures to keep them open after closure. Economic considerations have driven the industry to find ways to determine the optimal type, size and concentration of proppant that would enhance fracture conductivity and improve well performance. Therefore, direct laboratory conductivity measurements using real shale samples under realistic experimental conditions are needed for reliable hydraulic fracturing design optimization. A series of laboratory experiments was conducted to measure the conductivity of propped and unpropped fractures of Barnett shale using a modified API conductivity cell at room temperature for both natural fractures and induced fractures. The induced fractures were artificially created along the bedding plane to account for the effect of fracture face roughness on conductivity. The cementing material present on the surface of the natural fractures was preserved only for the initial unpropped conductivity tests. Natural proppants of difference sizes were manually placed and evenly distributed along the fracture face. The effect of proppant monolayer was also studied.Item The Method of Distributed Volumetric Sources for Forecasting the Transient and Pseudo-steady State Productivity of Multiple Transverse Fractures Intersected by a Horizontal Well(2011-02-22) Fan, DiangengThis work of well performance modeling is focused on solving problems of transient and pseudo-steady state fluid flow in a rectilinear closed boundaries reservoir. This model has been applied to predict and to optimize gas production from a horizontal well intercepted by multiple transverse fractures in a bounded reservoir, and it also provides well-testing solutions. The well performance model is designed to provide enhanced efficiency with the same reliability for pressure transient analysis, and well performance prediction, especially in complex well fracture configuration. The principle is to simplify the calculation of the pressure response to an instantaneous withdraw, which happens in other fractures, within a shorter computational time. This pressure response is substituted with the interaction between the two whole fractures. This method is validated through comparison to results of rigorous Distributed Volumetric Sources (DVS) method in simple symmetric fracture configuration, and to results of field production data for complex well/fracture configuration of a tight gas reservoir. The results show a good agreement in both ways. This model indicates the capability to handle the situations, such as: various well drainages, asymmetry of the fracture wings, and curved horizontal well. The advantage of this well performance model is to provide faster processing - reducing the computational time as the number of fractures increase. Also, this approach is able to be applied as an optimization and screening tool to obtain the best fracture configurations for reservoir development of economically marginal fields, in terms of the number and dimensions of fractures per well, also with external economic and operational constraints.