scholarly journals Development of a New Empirical Relation to Assess P-wave Velocity Anisotropy of Rocks

2021 ◽  
Author(s):  
Hassan Moomivand ◽  
Hussamuddin Moomivand ◽  
Rain Nikrouz ◽  
Rashid Azad
Keyword(s):  
Wave Velocity ◽  
Marcellus Shale ◽  
Empirical Relation ◽  
P Wave ◽  
Physical Parameters ◽  
Mica Schist ◽  
Velocity Anisotropy ◽  
P Wave Velocity ◽  
Wide Range ◽  
Different Types

Abstract Wave velocity as a simple nondestructive method is used for various applications in geotechnical engineering. Several physical parameters and anisotropy related to rock textural arrangements, schistosity and weakness planes such as cracks and joints affect the P-wave velocity (VP). First, VP anisotropy of quartz-mica schist as a common type of widespread metamorphic rock was compared with VP anisotropy of jointed homogeneous limestone specimens to clarify effect of these two different types of anisotropies. The results showed that the VP anisotropy of quartz-mica schist texture is stronger than the VP anisotropy of jointed limestone, because all body of quartz-mica schist specimens have VP anisotropy behavior. Many rocks are anisotropic and degree of anisotropy varies from one rock to another. Several investigations have been carried out on VP anisotropy but there is not a unique comprehensive relation to represent the influence of different degrees of anisotropy on the VP for different rocks. The relation between VP and angle (θ) between the axis of symmetry (perpendicular to weakness planes) with the wave propagation direction was analyzed for a wide range of anisotropy degree using the results of nine different types of rocks including: Angouran quartz-mica schist, Golgohar mica schist, amphibole schist, mica-quart schist, Marcellus shale, Withby shale WUK47B, WUK70 and WUK2, and Veroia-Polymylos gneiss. A new simple empirical relation fitted to all groups of results was obtained to assess VP for different degrees of anisotropies with a good correlation of determination (R2 = 0.937), low RMSE (RMSE = 320 m/s) and low CV (CV = 7.0%). P wave velocity anisotropy can simply be predicted by the developed relation using only two parameters of VP0 and VP90. A VP anisotropy classification diagram was also developed based on the different values of ε.

scholarly journals Metode Seismik dalam Pemodelan Fisis Letusan Gunung Lumpur Bledug Kuwu

2019 ◽  
Vol 2 (2) ◽  
pp. 61-66
Author(s):  
Ahmad Fauzi Pohan ◽  
Rusnoviandi Rusnoviandi
Keyword(s):  
Wave Velocity ◽  
Physical Modeling ◽  
Vertical Component ◽  
Dominant Frequency ◽  
P Wave ◽  
Physical Parameters ◽  
S Wave ◽  
Interesting Phenomenon ◽  
Central Java ◽  
P Wave Velocity

Aktivitas gunung lumpur Bledug Kuwu di Jawa  Tengah merupakan fenomena yang menarik dikaji menggunakan pemodelan fisis. Tujuan penelitian ini adalah mengetahui parameter dari medium gunung lumpur Bledug Kuwu. Adapun pemodelan fisis yang dilakukan dengan menggunakan media fisis akuarium berukuran 59 × 59 × 37,3 cm yang diisi material dari lumpur Bledug Kuwu. Sumber letusan dihasilkan dari tekanan kompresor yang dapat diatur kedalaman (10.5, 13, dan 15.5 cm) dan sudut (30o, 45o dan 60o) sumbernya. Sensor yang digunakan geophone komponen vertikal sebanyak 3 buah dengan durasi perekaman selama 5 dan 2,5 detik. Data diambil dengan frekuensi sampel 2 dan 4 kHz untuk masing-masing durasi perekaman. Konfigurasi sumber dan geophone dibuat sesuai dengan pemodelan fisisnya. Pengukuran desnsitas lumpur menunjukkan angka sebesar 1200 kg/m3. Berdasarkan hasil analisis seismogram model fisis diperoleh kecepatan perambatan gelombang-P pada medium lumpur Bledug Kuwu adalah sebesar 48,74 m/s,dan gelombang-S sebesar 28,14 m/s dengan frekuensi dominan antara 20 sampai 25 Hz.   Bledug Kuwu mud volcano activity in Central Java is an interesting phenomenon to be studied using both physical  modeling. The objective of this study was to determine the physical parameters of the medium of Bledug Kuwu. The Physical model was an aquarium with a dimension of 59 × 59 × 37.3 cm filled with Bledug Kuwu’s mud. The eruption source is generated by a compressor pressure that can be controled both the depth(10.5, 13, and 15.5 cm) and the angel of the source (30o, 45o and 60o). The resulting seismic signals were recorded by using 3 vertical component geophones for 10 and 5 seconds durations at a frequency of 2 and 4 kHz respectivel, mud density 1200 kg/m3 . The physical modeling shows that the P-wave velocity of the Bledug Kuwu’s medium is 48.7 m/s, S-wave velocity of Bledug Kuwu’s is 28,14 m/s  with a dominant frequency of 20 to 25 Hz.

scholarly journals A new compositionally based thermal conductivity model for plutonic rocks

2019 ◽  
Vol 219 (2) ◽  
pp. 1377-1394 ◽  
Author(s):  
S Jennings ◽  
D Hasterok ◽  
J Payne
Keyword(s):  
Thermal Conductivity ◽  
Wave Velocity ◽  
Geometric Model ◽  
Limited Range ◽  
P Wave ◽  
Similar Degree ◽  
Primary Control ◽  
Element Geochemistry ◽  
P Wave Velocity ◽  
Wide Range

SUMMARY Thermal conductivity is a physical parameter crucial to accurately estimating temperature and modelling thermally related processes within the lithosphere. Direct measurements are often impractical due to the high cost of comprehensive sampling or inaccessibility and thereby require indirect estimates. In this study, we report 340 new thermal conductivity measurements on igneous rocks spanning a wide range of compositions using an optical thermal conductivity scanning device. These are supplemented by a further 122 measurements from the literature. Using major element geochemistry and modal mineralogy, we produce broadly applicable empirical relationships between composition and thermal conductivity. Predictive models for thermal conductivity are developed using (in order of decreasing accuracy) major oxide composition, CIPW normative mineralogy and estimated modal mineralogy. Four common mixing relationships (arithmetic, geometric, square-root and harmonic) are tested and, while results are similar, the geometric model consistently produces the best fit. For our preferred model, $k_{\text{eff}} = \exp ( 1.72 \, C_{\text{SiO}_2} + 1.018 \, C_{\text{MgO}} - 3.652 \, C_{\text{Na}_2\text{O}} - 1.791 \, C_{\text{K}_2\text{O}})$, we find that SiO2 is the primary control on thermal conductivity with an RMS of 0.28 W m−1 K−1or ∼10 per cent. Estimates from normative mineralogy work to a similar degree but require a greater number of parameters, while forward and inverse modelling using estimated modal mineralogy produces less than satisfactory results owing to a number of complications. Using our model, we relate thermal conductivity to both P-wave velocity and density, revealing systematic trends across the compositional range. We determine that thermal conductivity can be calculated from P-wave velocity in the range 6–8 km s−1 to within 0.31 W m−1 K−1 using $k({V_p}) = 0.5822 \, V_p^2 - 8.263 \, V_p + 31.62$. This empirical model can be used to estimate thermal conductivity within the crust where direct sampling is impractical or simply not possible (e.g. at great depths). Our model represents an improved method for estimating lithospheric conductivity than present formulas which exist only for a limited range of compositions or are limited by infrequently measured parameters.

scholarly journals Analysis of Effects of Rock Physical Properties Changes from Freeze–Thaw Weathering in Ny-Ålesund Region: Part 2—Correlations and Prediction of Weathered Properties

2020 ◽  
Vol 10 (10) ◽  
pp. 3392 ◽  
Author(s):  
Keunbo Park ◽  
Bang Yong Lee ◽  
Kichoel Lee ◽  
Dongwook Kim
Keyword(s):  
Compressive Strength ◽  
Water Absorption ◽  
Wave Velocity ◽  
P Wave ◽  
Physical Parameters ◽  
Shore Hardness ◽  
Rock Composition ◽  
Freeze Thaw ◽  
Thaw Cycle ◽  
P Wave Velocity

From the examination of rock physical parameters’ changes of compressive strength, shore hardness, water absorption, P-wave velocity with increasing freeze–thaw cycles, correlations of these parameters were investigated. Rock samples were collected from Ny-Ålesund region in Norway. As compressive strength and shore hardness inherently have high uncertainties due to inhomogeneous rock composition and internal fissures and cracks, only the relationship between water absorption and P-wave velocity revealed high correlations, providing meaningful linear fitting equations. From the correlation analysis results and clear trends of increasing water absorption and decreasing P-wave velocity with increasing freeze–thaw cycle found in part one of the companion study, prediction equations of future changes of rock physical parameters are proposed using P-wave velocity or water absorption. In addition, future rock weathering grade changes with time can be predicted from estimation of water absorption or P-wave velocity change due to freeze–thaw cycles.

EXPERIMENTAL EVALUATION OF ULTRASONIC VELOCITIES AND ANISOTROPY IN THE TUSCALOOSA MARINE SHALE FORMATION

2020 ◽  
pp. 1-62 ◽  
Author(s):  
Jamal Ahmadov ◽  
Mehdi Mokhtari
Keyword(s):  
Wave Velocity ◽  
Mineralogical Composition ◽  
Organic Content ◽  
P Wave ◽  
S Wave ◽  
Velocity Anisotropy ◽  
Wave Velocities ◽  
Marine Shale ◽  
P Wave Velocity ◽  
Degree Of Anisotropy

Tuscaloosa Marine Shale (TMS) formation is a clay- and organic-rich emerging shale play with a considerable amount of hydrocarbon resources. Despite the substantial potential, there have been only a few wells drilled and produced in the formation over the recent years. The analyzed TMS samples contain an average of 50 wt% total clay, 27 wt% quartz and 14 wt% calcite and the mineralogy varies considerably over the small intervals. The high amount of clay leads to pronounced anisotropy and the frequent changes in mineralogy result in the heterogeneity of the formation. We studied the compressional (VP) and shear-wave (VS) velocities to evaluate the degree of anisotropy and heterogeneity, which impact hydraulic fracture growth, borehole instabilities, and subsurface imaging. The ultrasonic measurements of P- and S-wave velocities from five TMS wells are the best fit to the linear relationship with R2 = 0.84 in the least-squares criteria. We observed that TMS S-wave velocities are relatively lower when compared to the established velocity relationships. Most of the velocity data in bedding-normal direction lie outside constant VP/VS lines of 1.6–1.8, a region typical of most organic-rich shale plays. For all of the studied TMS samples, the S-wave velocity anisotropy exhibits higher values than P-wave velocity anisotropy. In the samples in which the composition is dominated by either calcite or quartz minerals, mineralogy controls the velocities and VP/VS ratios to a great extent. Additionally, the organic content and maturity account for the velocity behavior in the samples in which the mineralogical composition fails to do so. The results provide further insights into TMS Formation evaluation and contribute to a better understanding of the heterogeneity and anisotropy of the play.

Pyrolysis-induced P-wave velocity anisotropy in organic-rich shales

Geophysics ◽  
2014 ◽  
Vol 79 (2) ◽  
pp. D41-D53 ◽  
Author(s):  
Adam M. Allan ◽  
Tiziana Vanorio ◽  
Jeremy E. P. Dahl
Keyword(s):  
Wave Velocity ◽  
Elastic Anisotropy ◽  
Rock Physics ◽  
Confining Pressure ◽  
Source Rocks ◽  
Acoustic Properties ◽  
P Wave ◽  
Velocity Anisotropy ◽  
Geochemical Parameters ◽  
P Wave Velocity

The sources of elastic anisotropy in organic-rich shale and their relative contribution therein remain poorly understood in the rock-physics literature. Given the importance of organic-rich shale as source rocks and unconventional reservoirs, it is imperative that a thorough understanding of shale rock physics is developed. We made a first attempt at establishing cause-and-effect relationships between geochemical parameters and microstructure/rock physics as organic-rich shales thermally mature. To minimize auxiliary effects, e.g., mineralogical variations among samples, we studied the induced evolution of three pairs of vertical and horizontal shale plugs through dry pyrolysis experiments in lieu of traditional samples from a range of in situ thermal maturities. The sensitivity of P-wave velocity to pressure showed a significant increase post-pyrolysis indicating the development of considerable soft porosity, e.g., microcracks. Time-lapse, high-resolution backscattered electron-scanning electron microscope images complemented this analysis through the identification of extensive microcracking within and proximally to kerogen bodies. As a result of the extensive microcracking, the P-wave velocity anisotropy, as defined by the Thomsen parameter epsilon, increased by up to 0.60 at low confining pressures. Additionally, the degree of microcracking was shown to increase as a function of the hydrocarbon generative potential of each shale. At 50 MPa confining pressure, P-wave anisotropy values increased by 0.29–0.35 over those measured at the baseline — i.e., the immature window. The increase in anisotropy at high confining pressure may indicate a source of anisotropy in addition to microcracking — potentially clay mineralogical transformation or the development of intrinsic anisotropy in the organic matter through aromatization. Furthermore, the evolution of acoustic properties and microstructure upon further pyrolysis to the dry-gas window was shown to be negligible.

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