scholarly journals Grouting Reinforcement Technique in Wind Oxidation Zone by Power Law Superfine Cement Slurry Considering the Time-Varying Rheological Parameters

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Dengxing Zhu ◽  
Yu Guo ◽  
Wei Wang ◽  
Gangye Guo ◽  
Tieliang An
Keyword(s):  
Power Law ◽  
Coal Mine ◽  
Effective Diffusion ◽  
Oxidation Zone ◽  
Rheological Parameters ◽  
Time Varying ◽  
Cement Slurry ◽  
Permeability Characteristics ◽  
Grouting Pressure ◽  
Roof Strata

With the recovery of the wind oxidation zone in 13116 working face of Gubei Coal Mine as the engineering background, the occurrence condition of coal seam and the bedrock wind oxidation zone characteristics were analyzed. On this basis, the time-varying rheological parameters of superfine cement slurry and the permeability characteristic parameters of roof strata in wind oxidation zone were measured; then, a grout diffusion equation was established with the parameters obtained previously for the permeability characteristics of roof strata in the wind oxidation zone of Gubei Coal Mine. The grouting design was applied in actual engineering projects and its engineering effect has been proved to be satisfactory. The results indicate that superfine cement slurry whose water-cement ratio is 0.6 is a typical power-law slurry consistent with time-varying rheological parameters. It has better rheological properties during pumpable period, and its rheological parameters can be controlled by highly dispersive nano-SiO2 and polycarboxylate superplasticizer. For grouting in wind oxidized zone, comprehensive consideration must be given to effective permeability Ke, porosity  ∅ , and time-varying rheological parameters c0, k, and n. To realize effective diffusion of grouting in coal and rock mass, grouting pressure and diffusion time must be reasonably designed rather than excessively increased.

Relaxation-induced flow of an Ellis fluid in a smooth fracture

2021 ◽  
Author(s):  
Valentina Ciriello ◽  
Alessandro Lenci ◽  
Sandro Longo ◽  
Vittorio Di Federico
Keyword(s):  
Power Law ◽  
Discharge Rate ◽  
Vertical Plane ◽  
Elastic Response ◽  
Rheological Parameters ◽  
Dimensionless Number ◽  
Late Time ◽  
Time Behavior ◽  
Time Varying ◽  
Fracturing Fluids

<p>The process known as hydrofracturing, aimed at improving reservoir productivity, is complex and includes several steps. During the first, high-pressure injection, a network of fractures and cracks is created in the stimulated zone; then proppant is introduced into the network to open the supporting fractures; when the injection stops, the pressure drops and elastic relaxation of the fluid-driven fractures pushes the fracturing fluid back into the injection well. Once recovered, these fluids are typically processed for reuse due to their versatility and economic value; in addition, unrecovered fluid tends to compromise fracture conductivity or migrate into the subsurface environment. Optimizing the recovery rate is critical regardless of the reservoir product (oil, gas, heat). Because the goal is to create fractures that remain open, inevitably some of the fluid is not drained.</p><p>The rheology of fracturing fluids is typically described by a non-Newtonian rheology, showing a nonlinear relationship between stress and strain; this allows for flexibility and several design goals to be achieved at the same time.</p><p>We adopt a conceptual model to represent the fracture medium, consisting of a single planar fracture with relaxing walls, exerting a force on the fluid proportional to <em>h<sub>λ</sub></em>, with <em>h</em> the time-varying aperture and <em>λ</em> a non-negative exponent; an overload of <em>f</em><sub>0</sub> on the fracture can help slow or accelerate the closure process. The fracture is in a vertical plane perpendicular to a horizontal hole or in a horizontal plane perpendicular to a vertical hole. At time <em>t</em> = 0, pressure <em>p</em><sub>e</sub> at the outlet begins to act, the elastic response of the wall compresses the fluid and forces a backflow to the outlet as a result of the no-flow boundary condition at <em>x</em>=<em>L</em>. Gravity effects are absent in horizontal fractures and negligible with respect to pressure gradients for fractures in any other plane.  </p><p>Fluid rheology is described by the three-parameter Ellis model, which well represents the typical shear-thinning rheology of hydro-fracturing fluids and the Newtonian and power-law coupling behavior at low and high shear rates, respectively.</p><p>Under viscous flow and lubrication approximation, the time-varying aperture and discharge rate, the space- and time-varying pressure field, and the time to drain a given fraction of the fracture volume are derived as a function of geometry (length and initial aperture), elastic wall parameters, fluid properties, outlet pressure and overload. The parameters of the problem are combined in a dimensionless number <em>N</em> that tunes the interplay between Newtonian and power-law rheology. The late-time behavior of the system is practically independent of the rheology, since the Newtonian nature of the fluid prevails at low shear stress. In particular, the aperture and discharge scale are asymptotic with time as <em>t </em>∝ 1/(2+λ) and <em>t </em>∝ 1/(3+λ) for <em>p</em><sub>e</sub>-<em>f</em><sub>0</sub>=0; otherwise, the aperture tends to a constant, residual value proportional to (<em>p</em><sub>e</sub>-<em>f</em><sub>0</sub>)<sup>λ</sup>. A case study with equally spaced fractures adopting realistic geometric, mechanical and rheological parameters is examined: two fluids normally used in fracking technology exhibit completely different behaviors, with backflow dynamics and drainage times initially not dissimilar, and subsequently varying by orders of magnitude.</p>

Effect Analysis of Nitrogen Injection on the Variation of “Oxidation Zone” in Coal Mine Gob Based on Numerical Simulation

2016 ◽  
Vol 9 (1) ◽  
pp. 47-54
Author(s):  
Jing Shen ◽  
Mingran Chang
Keyword(s):  
Numerical Simulation ◽  
Coal Mine ◽  
Heat Dissipation ◽  
Spontaneous Combustion ◽  
Oxidation Zone ◽  
Effect Analysis ◽  
Mine Fire ◽  
Nitrogen Injection ◽  
The Difference ◽  
Residual Coal

One of the main reasons for coal mine fire is spontaneous combustion of residual coal in gob. As the difference of compaction degree of coal and rock, the underground gob can be considered as a porous medium and divided into “three zones” in accordance with the criteria. The “three zones” are “heat dissipation zone”, “oxidation zone” and “choking zone”, respectively. Temperature programming experiments are taken and numerical simulation with obtained experimental data is utilized to analyze the distribution of “three zones” in this paper. Different width and depth of “oxidation zone” are obtained when the inlet air velocity is changed. As the nitrogen injection has inhibition effect on spontaneous combustion of residual coal in gob, nitrogen is injected into the gob. The widths of “oxidation zone” are compared before and after nitrogen injection. And ultimately the optimum location and volume of nitrogen injection are found out.

scholarly journals Methane Emission during Gas and Rock Outburst on the Basis of the Unipore Model

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1999 ◽  
Author(s):  
Skoczylas Norbert ◽  
Anna Pajdak ◽  
Katarzyna Kozieł ◽  
Leticia Teixeira Palla Braga
Keyword(s):  
Coal Mine ◽  
Effective Diffusion ◽  
Measurement Data ◽  
Sorption Isotherms ◽  
Sieve Analysis ◽  
Measurement Systems ◽  
Upper Silesian Coal Basin ◽  
Tectonic Disturbances ◽  
Concentration Changes ◽  
Time Courses

The goal of this paper is to analyze the phenomenon of gas emission during a methane and coal outburst based on the unipore Crank diffusion model for spherical grains and plane sheets. Two occurrences in the Upper Silesian Coal Basin were analyzed: an outburst in a Zofiówka coal mine in 2005 and an outburst in a Budryk coal mine in 2012. Those two outbursts differed considerably. The first one was connected with an unidentified tectonic disturbance in the form of a triple, interlocking fault, and the other one is an example of an outburst in an area free from tectonic disturbances. The model analysis required laboratory tests in order to determine the sorption properties of coals from post-outburst masses. Sorption isotherms and the values of the effective diffusion coefficient were specified. The post-outburst masses were subjected to sieve analysis and the grain composition curves were plotted. The researchers also used the measurement data provided by proper mine services, such as the methane content, the volume of post-outburst masses, and the time courses of CH4 concentration changes in excavations. They were recorded by methane measurement systems in the mines.

Thermorheological Characterization of Elastoviscoplastic Carbopol Ultrez 20 Gel

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
M. A. Hassan ◽  
Manabendra Pathak ◽  
Mohd. Kaleem Khan
Keyword(s):  
Experimental Investigation ◽  
Yield Stress ◽  
Elastic Properties ◽  
Viscous Dissipation ◽  
Power Law ◽  
Effect Of Temperature ◽  
Rheological Parameters ◽  
Frequency Range ◽  
Power Law Index

The temperature and concentration play an important role on rheological parameters of the gel. In this work, an experimental investigation of thermorheological properties of aqueous gel Carbopol Ultrez 20 for various concentrations and temperatures has been presented. Both controlled stress ramps and controlled stress oscillatory sweeps were performed for obtaining the rheological data to find out the effect of temperature and concentration. The hysteresis or thixotropic seemed to have negligible effect. Yield stress, consistency factor, and power law index were found to vary with temperature as well as concentration. With gel concentration, the elastic effect was found to increase whereas viscous dissipation effect was found to decrease. Further, the change in elastic properties was insignificant with temperature in higher frequency range of oscillatory stress sweeps.

Zaczyny cementowe z dodatkiem nanorurek węglowych do uszczelniania otworów wiertniczych o wysokiej temperaturze i ciśnieniu złożowym (150°C, 90 MPa)

Nafta-Gaz ◽  
2021 ◽  
Vol 77 (5) ◽  
pp. 323-331
Author(s):  
Miłosz Kędzierski ◽  
◽  
Marcin Rzepka ◽  
Keyword(s):  
Carbon Nanotubes ◽  
Compressive Strength ◽  
High Temperature ◽  
Rheological Parameters ◽  
External Diameter ◽  
Mechanical Parameters ◽  
Cement Slurry ◽  
Significant Information ◽  
High Temperature And Pressure ◽  
Temperature And Pressure

The article presents the results of the influence of carbon nanotubes on the mechanical parameters of cement stones under high temperature and pressure conditions (150°C, 90 MPa). The tests used multi-walled carbon nanotubes (MWCNTs) with an external diameter of 10–20 nm and a length of 10–30 μm. Cement slurries contained 0.1% of CNTs bwoc (by the weight of cement). Laboratory tests of cement slurries were carried out at the Oil and Gas Institute – National Research Institute. The tests were carried out under conditions of increased pressure and temperature at 150°C, 90 MPa. Cement slurries were prepared on the basis of class G drilling cement. Developing recipes were guided by the requirements to be met by cement slurry for the cementing of casing in the conditions of high temperature and reservoir pressures. The densities of tested slurries ranged from 1900 kg/m3 to 2250 kg/m3 (slurries with the addition of hematite). The cement slurries were tested for density, fluidity, rheological parameters, filtration and thickening time. Compressive strength tests and measuring adhesion were carried out after 2, 7, 14 and 28 days. Cement slurry recipes with very good technological parameters were developed and after curing (after 28 days of hydration) had very high values of compressive strength, reaching up to 45 MPa. Cements were characterized by high values of adhesion to pipes reaching up 7 MPa after 28 days. The research showed significant information about possible applications of carbon nanotubes to modify the cement slurry under conditions of high temperature and pressure. The conducted tests confirmed that the addition of even small amounts of CNTs improves the mechanical parameters of the cement stone compared to the base sample without such addition, and also reduces the thickening time of cement slurries and reduces filtration. It is investigated that CNTs addition increases the viscosity and yield point of cement slurry. As a result, slurries with the addition of MWCNTs will more effectively displace the mud from the borehole and significantly affect the quality of cementation.

scholarly journals Inversion of flow Measurements for Stress and Rheological Parameters in a Valley Glacier

1973 ◽  
Vol 12 (64) ◽  
pp. 19-44
Author(s):  
Charles F. Raymond
Keyword(s):  
Shear Stress ◽  
Power Law ◽  
Measurement Errors ◽  
Effective Viscosity ◽  
Three Dimensional ◽  
Rheological Parameters ◽  
Mean Stress ◽  
Flow Measurements ◽  
Anomalous Zone ◽  
Flow Law

AbstractMethods are developed for determining the distributions of stress and effective viscosity in a glacier, under the assumptions: the ice is quasi-viscous, the flow is time independent, and acceleration forces are negligible. Measurements of the three-dimensional distribution of velocity are needed for their application. The differential equations of mechanical equilibrium, expressed in terms of viscosity, strain-rate components, mean stress, and their gradients, are viewed as equations to be solved for viscosity and mean stress subject to boundary conditions at the free upper surface. For certain rectilinear flow patterns, unique distributions of stress and effective viscosity can always be derived. For more complicated flow this is not necessarily so. However, it is still possible to choose the best values of rheological parameters in any trial flow law based on the requirement that the residuals to the equations of equilibrium be minimized in a mean-square sense. The techniques are applied to measurements of internal deformation made in nine bore holes on the Athabasca Glacier. At the center line the magnitude of the surface-parallel shear stress increases with depth more slowly than would be expected from a standard shape factor correction or the theoretical distribution of Nye. Correspondingly the lateral distribution of lateral shear stress shows the opposite relationships. In the lower one- to two-thirds of the depth corresponding to a range in effective stress from about 0.5 to 1.2 bars, the gross rheology of the ice is not distinguishably different from the experimentally determined flow law of Glen (n = 4.2, T = 0.02° C) as generalized by Nye. The results do not support the conclusion that the effective viscosity is higher than would be expected from Glen’s experiments as indicated by the more limited measurements of Paterson and Savage. Power-law parameters derived for the different bore holes considered separately show a spread, which suggests some rheological inhomogeneity. However, no definite conclusions can be drawn, because of direct measurement errors at the bore holes and less definable uncertainty in the interpolated distribution of velocity between the holes. The upper one- to two-thirds of the glacier constitutes an anomalous zone in which there is either a strong effect from a complex distribution of stress arising from longitudinal stress gradients or more complicated rheology than in a homogeneous power-law material.

scholarly journals On the existence of earthquake precursors

1999 ◽  
Vol 42 (5) ◽  
Author(s):  
F. Evison
Keyword(s):  
Empirical Research ◽  
Earthquake Prediction ◽  
Power Law ◽  
Earthquake Precursors ◽  
Time Varying ◽  
Formal Testing ◽  
High Degree ◽  
Experimental Stage

Earthquake prediction based on precursors can aim to provide fully quantified, time-varying, synoptic forecasts, which do not depart from physical and geological principles, and are amenable to formal testing. These features are in contrast to the traditional occultist or soothsayer style of prediction. The recently-advanced, pre-emptive hypothesis that earthquakes are intrinsically unpredictable, and precursors non-existent, is also amenable to testing: it is refuted by the well-known relations between mainshocks and aftershocks. These relations show that a set of aftershocks is to a high degree predictable from the mainshock, so that, as a matter of principle, the mainshock is a precursor to its aftershocks. This result is compatible with the power-law property of seismicity, on which the unpredictability hypothesis is based. Empirical research on most precursors is difficult because of the scarcity of data, and is still largely at the anecdotal stage. Additional difficulties at the experimental stage are exemplified by the failure of the Tokai and Parkfield experiments to advance the study of precursors as planned. A comparative abundance of data is available on seismicity anomalies, and research on this type of precursor is progressing towards the operational stage.

scholarly journals Continuous Magnitude Production of Loudness

2021 ◽  
Vol 12 ◽  
Author(s):  
Josef Schlittenlacher ◽  
Wolfgang Ellermeier
Keyword(s):  
Power Law ◽  
Line Length ◽  
Time Varying ◽  
Magnitude Production ◽  
Consistency Check ◽  
Regression Effects ◽  
Systematic Biases ◽  
Behavioural Experiments ◽  
The Given ◽  
Stevens’S Power Law

Continuous magnitude estimation and continuous cross-modality matching with line length can efficiently track the momentary loudness of time-varying sounds in behavioural experiments. These methods are known to be prone to systematic biases but may be checked for consistency using their counterpart, magnitude production. Thus, in Experiment 1, we performed such an evaluation for time-varying sounds. Twenty participants produced continuous cross-modality matches to assess the momentary loudness of fourteen songs by continuously adjusting the length of a line. In Experiment 2, the resulting temporal line length profile for each excerpt was played back like a video together with the given song and participants were asked to continuously adjust the volume to match the momentary line length. The recorded temporal line length profile, however, was manipulated for segments with durations between 7 to 12 s by eight factors between 0.5 and 2, corresponding to expected differences in adjusted level of −10, −6, −3, −1, 1, 3, 6, and 10 dB according to Stevens’s power law for loudness. The average adjustments 5 s after the onset of the change were −3.3, −2.4, −1.0, −0.2, 0.2, 1.4, 2.4, and 4.4 dB. Smaller adjustments than predicted by the power law are in line with magnitude-production results by Stevens and co-workers due to “regression effects.” Continuous cross-modality matches of line length turned out to be consistent with current loudness models, and by passing the consistency check with cross-modal productions, demonstrate that the method is suited to track the momentary loudness of time-varying sounds.

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