Rock Physics Research Papers - Academia.edu (original) (raw)

Crack damage leading to failure in rocks can be accumulated through cyclic stressing in the crust. However, the vast majority of experimental studies to investigate cyclic stressing apply conventional triaxial stress states (σ 1 > σ 2 = σ... more

Crack damage leading to failure in rocks can be accumulated through cyclic stressing in the crust. However, the vast majority of experimental studies to investigate cyclic stressing apply conventional triaxial stress states (σ 1 > σ 2 = σ 3), while in nature the state of stress in the crust is generally truly triaxial (σ 1 > σ 2 > σ 3). Furthermore, the magnitude of these crustal stresses can vary over time and their orientations can also rotate over time, generating multiple crack populations and bulk anisotropic crack damage. We investigate the evolution of crack damage under both conventional and true triaxial stress conditions by sequentially and cyclically varying stresses in all three principal directions on cubic samples of dry sandstone using independently controlled stress paths. We have measured, simultaneously with stress, the bulk acoustic emission output, as a proxy for crack damage. We report a directionally controlled crack damage memory effect which has implications for the approach to failure in complex tectonic stress environments. Plain Language Summary Fractures that lead to failure and faulting in rocks accumulate over time with increasing amounts of stress. While a considerable amount of research has been devoted to understanding how cyclic stresses lead to the development of crack damage, very little work has considered how this damage evolves with direction. The lack of work on this topic is partly due to the type of experimental apparatus required to conduct suitable tests. In order to replicate multiple populations of crack damage in different directions, a true triaxial loading apparatus is needed. Such an apparatus replicates the general state of stress in the crust and allows those stresses to be varied with direction. It is well known that the stress field around fault zones, in volcanoes, and in geothermal systems can be complex and can rotate over time. By conducting experiments using a novel true triaxial apparatus we find a directionally controlled crack damage memory effect which has implications for the approach to failure of critically stressed rocks in complex tectonic stress environments. As such, these experimental results will be of interest to those studying fault zones and volcanic processes.

Due to the development of denser permanent Global Navigation Satellite System (GNSS) networks over the last decade, the observation of transient deformations has significantly increased, mainly in high strain-rate zones. We analyzed the... more

Due to the development of denser permanent Global Navigation Satellite System (GNSS) networks over the last decade, the observation of transient deformations has significantly increased, mainly in high strain-rate zones. We analyzed the data from a group of permanent GNSS sites on the N-Adria microplate, where anomalous southward tilting and low-frequency tremors preceded the 1976 M w = 6.4 earthquake. We present records from different stations of a transient signal with an approximately 2-year period that propagated through the northern edge of Adria, in a region 150 km wide. This represents the first time a transient deformation event has been observed in a continental collision area. We exclude surface and groundwater hydrological load effects because we corrected the data for such effects at seasonal, annual, and multiyear scales. The movement is initially upward, except in one location, with slight tilting parallel to the direction of the main tectonic structures. Later, the opposite behavior is observed. The novel methods used include earthquake location techniques and tomographic inversion of the arrival times. These methods demonstrated that the transient source was located spatially and temporally close to the 2004 M w = 5.2 event in Bovec (Slovenia), attributed to the activity of the Ravne fault. We interpret the transient rises as the expression of a porosity wave, possibly produced by fault valve behavior of the NW tip of the Ravne fault. The propagation velocity is consistent with this hypothesis. As a further test, we invert the arrival times of the transient through hydraulic tomography to obtain hydraulic diffusivity: the values are compatible with the lithotypes present in the region and the literature. By substituting the tomographic velocity and diffu-sivity in the solitary/porosity wave equation, we infer an initial effective stress of approximately 0.23 bar, sufficient to alter the equilibrium of some fault segments and influence the subsequent seismicity.

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will... more

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

The Karlıova triple junction (KTJ) in eastern Turkey has been subjected to incremental deformation resulting in complex kinematic and mechanical interactions throughout the upper crust. These interactions have generated tectonic... more

The Karlıova triple junction (KTJ) in eastern Turkey has been subjected to incremental deformation resulting in complex kinematic and mechanical interactions throughout the upper crust. These interactions have generated tectonic inversions and uplift, extensive seismicity and volcanism. The regional tectonics generate local stresses, some of which are favorable to magma transport and thermal water circulation throughout the lithosphere. Here we evalauate hydrogeochemical, geological and numerical results relating to the mechanism of thermal fluid circulation around the KTJ. Hydrogeochemistry of the samples indicates that the thermal water springs are probably heated by steam. Volcanic rocks at the site appear to be the host rock owing to the enrichment of Na + and Cl − ions in water and the abundance of these elements in minerals of the volcanic rocks. In addition, it is clear that the thermal fluids are sourced from depth and migrate through permeable networks of faults. The effects of crustal heterogeneities, in particular the geometry and mechanical properties of many faults and layers, on thermal fluid circulation in relation to active magma chambers were investigated under a variety of different mechanical conditions. The numerical results indicate very close relationships between the stress field causing faulting and thermal fluid movement in the KTJ. The effect of thermal transfer was modeled with depth throughout the crust and along the the crustal surface. The models show that some faults encourage thermal fluid circulation below the Varto and Özenç volcanoes. Hydrogeochemical, geological and numerical results suggest that magmas residing beneath both the Varto caldera and the Özenç volcano are the main heat source for thermal fluid in the Varto region. Fluid-solid interactions and fluid circulation models show that the permeable faults are important factors affecting heat transport and fluid circulation. In a series of thermal fluid flow models we probe the mechanism for fluid and gas transport from the 900°C 'hot' zone around the deep magma chambers and investigate how heat is lost throughout the crust on the way to the surface and so eventually creates water channels of temperatures between 50 to 60°C.

Carbonate reservoir is known as heterogeneous reservoir due to its pore complexity caused by depositional setting and diagenetic process. This complexity can create comprehension about its storage capacity and flow capacity, including... more

Carbonate reservoir is known as heterogeneous reservoir due to its pore complexity caused by depositional setting and diagenetic process. This complexity can create comprehension about its storage capacity and flow capacity, including water saturation. Reservoir characterization method through Flow Zone Indicator (FZI) can be useful to divide reservoir rock based on its flow unit and irreducible water saturation as well. Reservoir characterization is applied to Kujung formation, in Jago and Bravo Structure, North East Java Basin which has an invalid calculation Archie's water saturation. Firstly, flow unit is identified by FZI, then water saturation of the reservoir is then calculated by Leverett J-Function method which every flow unit has its irreducible water saturation. From FZI method, Kujung formation can be
divided into three flow units with their own characteristics. Flow unit 1 has channeling pore type and 0.25 Swirr value, flow unit 2 has vuggy pore type and 0.39 Swirr value, while flow unit 3 has highly cemented interparticle pore type and 0.43 Swirr value. Water saturation, calculated by using Leverett J-Function method, provides a more precise result compared to Archie’s water saturation method, which has been validated by fractional flow test in Kujung reservoir interval. It is inferred that the reservoir characterization implies an excellent prediction of water saturation by using J-Function Method.

The discrimination of hydrocarbon (gas or oil) facies from non-hydrocarbon (wet sands) facies is an important goal in quantitative seismic interpretation and reservoir estimation. The differentiation of hydrocarbon facies from... more

The discrimination of hydrocarbon (gas or oil) facies from non-hydrocarbon (wet sands) facies is an important goal in quantitative seismic interpretation and reservoir estimation. The differentiation of hydrocarbon facies from non-hydrocarbon in Mississauga Formation of early Cretaceous in Penobscot area is a difficult task due to smaller net pay thickness and shaly sand intervals. Based on seismic interpretation and wireline logs, five sand plays are identified in the middle of Mississauga Formation. Four sands have hydrocarbons while top of sand 5 represents hydrocarbon water transition zone. Among these four, the pay sand 4 is analyzed for hydrocarbon facies. Wireline logs and seismic data are used to derive various amplitude versus offset (AVO) based attributes such as: acoustic (I P) and shear (I S) impedances, Poisson ratio (σ) etc. Further, the combined attributes e.g., product of Lamé parameters (µ, λ) with density (ρ), their ratio (λ/μ), difference between bulk modulus (K) and shear modulus (µ), ∆µρ/µρ, Δ(λ/μ + 2)(λ/μ + 2) and the pore space modulus (Κ P) are also analyzed to find out the best attribute as a hydrocarbon facies discriminator from non-hydrocarbon facies in the shale imbedded pay sand 4 of Mississauga Formation. First, petrophysical parameters such as P and S wave impedances, Lamé's parameters etc. are extracted from log data. Then, appropriate pairs of seismic attributes are crossplot-ted so that the hydrocarbon and non-hydrocarbon facies cluster together for quick identification and interpretation. Gamma ray index is crossplotted against spontaneous potential log to mark sand and shale facies. Fluid substitution modeling for various fluid types and saturation is also done which demonstrate that the cross-plots between different rock physics parameters can be used to distinguish between reservoir fluids. Our analysis reveals single P-wave based attributes are not sufficient to discriminate fluids thus the use of multi-attributes such as K P , λρ and Κ-µ is more effective to discriminate the hydrocarbon and non-hydrocarbon facies. The analysis of these cross-plots was done to map the reservoir sands and the hydrocarbon-water contact.

Lebih dari 50% produksi minyak dan gas bumi di dunia dihasilkan oleh reservoir karbonat. Reservoir karbonat sulit untuk dikarakterisasi dikarenakan kompleksitas tipe pori batuan karbonat. Karakteristik yang berbeda antara batuan karbonat... more

Lebih dari 50% produksi minyak dan gas bumi di dunia dihasilkan oleh reservoir karbonat. Reservoir karbonat sulit untuk dikarakterisasi dikarenakan kompleksitas tipe pori batuan karbonat. Karakteristik yang berbeda antara batuan karbonat dan batupasir juga menjadi hambatan untuk memprediksi kondisi reservoir karbonat. Tipe pori batuan karbonat yang dapat dijelaskan menggunakan aspect ratio menjadi topik penelitian yang harus dilakukan. Pemodelan aspect ratio dipengaruhi oleh ketepatan estimasi modulus elastik matriks batuan. Estimasi nilai modulus elastik matriks batuan untuk setiap kedalaman sulit untuk dilakukan dikarenakan keterbatasan data X-Ray Diffraction (XRD) yang tersedia. Data XRD tersebut hanya memuat informasi fraksi masing-masing mineral untuk beberapa kedalaman tanpa adanya informasi mengenai nilai modulus elastik mineral pada lokasi penelitian. Daerah penelitian termasuk dalam Formasi Ngimbang, Cekungan Jawa Timur Utara. Pada penelitian ini, penentuan modulus elastik matriks batuan dilakukan dengan mengkombinasikan beberapa pendekatan seperti model Krief, Dvorkin, Wang, dan Voigt-Reuss-Hill (VRH) dan menggunakan pendekatan J.H Schön sebagai pendekatan akhir. Adapun estimasi tipe pori dilakukan dengan menggunakan metode Kuster-Toksöz dengan nilai aspect ratio guidance didapatkan melalui pendekatan Biot Gassmann dan Zimmerman. Hasil penelitian menunjukkan pendekatan fisika batuan dapat memberikan kontribusi yang baik dalam mengidentifikasi tipe pori pada batuan karbonat. Hasil pemodelan kecepatan gelombang P dan S pada penelitian ini memberikan nilai error minimum dan koefisien korelasi maksimum dan dapat digunakan untuk menganalisis hubungan tipe pori dengan zona reservoir prospektif yang tersaturasi minyak bumi. Analisis lebih lanjut mengenai zona reservoir prospektif dapat dilakukan dengan menghubungkan hasil analisis tipe pori pada sumur “LGK” dengan sumur-sumur lainnya agar diketahui persebaran bentuk porinya secara horisontal.

The present study demonstrates the application of seismic petrophysics and amplitude versus angle (AVA) forward modeling to identify the reservoir fluids, discriminate their saturation levels and natural gas composition. Two case studies... more

The present study demonstrates the application of seismic petrophysics and amplitude versus angle (AVA) forward modeling to identify the reservoir fluids, discriminate their saturation levels and natural gas composition. Two case studies of the Lumshiwal Formation (mainly sandstone) of the Lower Cretaceous age have been studied from the Kohat Sub-basin and the Middle Indus Basin of Pakistan. The conventional angle-dependent reflection amplitudes such as P converted P (RPP) and S (RPS), S converted S (RSS) and P (RSP) and newly developed AVA attributes (ΔRPP, ΔRPS, ΔRSS, and ΔRSP) are analyzed at different gas saturation levels in the reservoir rock. These attributes are generated by taking the differences between the water wet reflection coefficient and the reflection coefficient at unknown gas saturation. Intercept (A) and gradient (B) attributes are also computed and cross-plotted at different gas compositions and gas/water scenarios to define the AVO class of reservoir sands. The numerical simulation reveals that ΔRPP, ΔRPS, ΔRSS, and ΔRSP are good indicators and able to distinguish low and high gas saturation with a high level of confidence as compared to conventional reflection amplitudes such as P-P, P-S, S-S and S-P. In A-B cross-plots, the gas lines move towards the fluid (wet) lines as the proportion of heavier gases increase in the Lumshiwal Sands. Because of the upper contacts with different sedimentary rocks (Shale/Limestone) in both wells, the same reservoir sand exhibits different response similar to AVO classes like the class I and class IV. This study will help to analyze gas sands by using amplitude-based attributes as direct gas indicators in further gas drilling wells in clastic successions.

Reservoir core measurements can help guide seismic monitoring of fluid-induced pressure variations in tight fractured reservoirs , including those targeted for supercritical CO 2 injection. We have developed the first seismic-frequency "... more

Reservoir core measurements can help guide seismic monitoring of fluid-induced pressure variations in tight fractured reservoirs , including those targeted for supercritical CO 2 injection. We have developed the first seismic-frequency " room-dry " measurements of fracture-specific shear stiffness, using artificially fractured standard granite samples with different degrees of mating , a well-mated tensile fracture from a dolomite reservoir core, as well as simple roughened polymethyl methacrylate (PMMA) surfaces. We have adapted a low-frequency (0.01–100 Hz) shear modulus and attenuation apparatus to explore the seismic signature of fractures and understand the mechanics of asperity contacts under a range of normal stress conditions. Our instrument is unique in its ability to measure at low-normal stresses (0.5– 20 MPa), simulating " open " fractures in shallow or high-fluid-pressure reservoirs. The accuracy of our instrument is demonstrated by calibration and comparison with ultrasonic measurements and low-frequency direct shear measurements of intact samples from the literature. Pressure-sensitive film was used to measure real contact area of the fracture surfaces. The fractured shear modulus for most of the samples shows an exponential dependence on the real contact area. A simple numerical model, with one bonded circular asperity, predicts this behavior and matches the data for the simple PMMA surfaces. The rock surfaces reach their intact moduli at lower contact area than the model predicts, likely due to more complex geometry. Finally, we apply our results to a linear-slip interface model to estimate reflection coefficients and calculate S-wave time delays due to the lower-wave velocities through the fractured zone. We find that cross-well surveys could detect even well-mated hard-rock fractures, assuming the availability of high-repeatability acquisition systems.

Reservoir Characterization involves a holistic approach of describing a reservoir by integrating geologic, geophysical, petrophysical and reservoir engineering using all available data for the characterization of the reservoir’s geometric... more

Reservoir Characterization involves a holistic approach of describing a reservoir by integrating geologic, geophysical, petrophysical and reservoir engineering using all available data for the characterization of the reservoir’s geometric features (including structural and stratigraphic controls) and Petrophysical properties (including porosity, permeability and fluid saturation). The focus is to understand and identify the flow units of the reservoir and predict the inter-well distributions of relevant reservoir properties. JAY field was characterized via Petrophysical analysis, seismic interpretation and modelling, and rock physics analysis. Porosity and permeability models were generated and combined with petrophysical analysis in characterizing the delineated reservoirs. The rock physics cross-plots were used to quality check the results from the seismic and Petrophysical analysis. The structural interpretation of the 3D seismic data of the field revealed anticlinal structures (four-way closure) which is fault assisted and can thus allow hydrocarbon accumulation. Four of the faults are major listric faults that trend in the Northeast Southwest direction. Amongst the remaining fourteen minor faults, five of them are synthetic faults whose sense of displacement is similar to its associated major faults while others are Antithetic faults. Four horizons were established which indicated the top and base of the two reservoirs. The Petrophysical analysis indicated that the reservoirs have good pore interconnectivity (Average ∅𝑒𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒= 24% & 21% and Average 𝐾𝑎𝑣𝑒𝑟𝑎𝑔𝑒 = 9701md & 7737md for Sand A and B respectively.) The rock physics analysis confirmed the result obtained from the Petrophysical analysis and furthermore, it showed that the lithologies within the lower portion of the reservoir were partially cemented. Also, the reservoir is found to be predominated by water followed by gas by both rock physics and petrophysical analysis.

The modeling and prediction of transport and elastic properties for sandstones are critical steps in the exploration and appraisal of hydrocarbon reservoirs, particularly in deepwater settings where seismic data are abundant and well... more

The modeling and prediction of transport and elastic properties for sandstones are critical steps in the exploration and appraisal of hydrocarbon reservoirs, particularly in deepwater settings where seismic data are abundant and well costs are high. Reliable multiphysics modeling of reservoir rocks requires robust models that respect the underlying geologic character and microstructure of the geomaterial and honor the measured properties. We have developed a case study that integrates traditional laboratory measurements with computational methods to quantify and relate physical properties of reservoir sandstones. We evaluate the complementary use of digital rock simulations as a practical technology that adds physical insight into the development and calibration of rock-property relationships. We also determine the challenges faced while applying digital rock physics to interpret laboratory data, and the steps taken to overcome those limitations. Combining physical and computational methods, we achieve an improved understanding of the link between geologic properties (sorting , microporosity) with transport (single-phase permeability, electrical conductivity) and elastic properties (moduli). Combining physical measurements with numerical computations has enhanced our understanding of multiphysics relationships in a heterogeneous sandstone reservoir.

The onshore portion of the Southwest Betara (SWB) Field is in the Jabung Block of the South Sumatra Basin, approximately 250 km south of Singapore. This field, discovered in 2005, is currently operated by PetroChina International Jabung... more

In this paper we examine the relationship between rock properties and seismic data. We present a framework based on AVO principles which assists in the interpretation of seismic data. The method discussed here weaves together principles... more

In this paper we examine the relationship between rock properties and seismic data. We present a framework based on AVO principles which assists in the interpretation of seismic data. The method discussed here weaves together principles from the following: (i) relative rock physics, (ii) rock physics templates, and (iii) elastic impedance, The result is a relative rock physics template defined in terms of elastic impedance parameters. It provides a useful insight to seismic parameters in cross-plot space.

One hundred rocks from representative Tertiary sedimentary basins in Japan, most of which are fine- and medium-grained clastic rocks, ranging Pliocene to Oligocene in age, were deformed at confining pressures up to 2,500kgf/cm2 at room... more

One hundred rocks from representative Tertiary sedimentary basins in Japan, most of which are fine- and medium-grained clastic rocks, ranging Pliocene to Oligocene in age, were deformed at confining pressures up to 2,500kgf/cm2 at room temperature, in a strain rate of 10-4 to 10-6/sec. All were tested under compression on dry cylindrical samples of 39.0mm in length and 19.5mm in diameter.
The results of experiments were tabulated in Table 4, The mechanical properties of sedimentary rocks have a wide range of value and are much influenced by lithological and geological factors. We tried to find relations among strength, confining pressure, deformational behavior, angle of fracture, strain at fracturing, failure type, porosity, grain size, axial shortening, sampled depth, elastic wave velocity, geologic age, stratigraphic level and tectonic environment. The mode of deformation, angle of fracture, and strain at fracturing are related to the ratio of shearing stress to normal stress on the plane of fracture or to the ratio of the maximum strength to the confining pressure. The failure type corresponds alrnost to the deformational behavior, and the change among failure types seems to be continuous. The " visco-ductile " flow is observed in extreme porous rocks, possibly because the framework is crushed by higher pressure than formerly applied. The strength of sedimentary rocks increases with diminution of porosity. Because of compaction, the rocks become, generally, stronger and less ductile with the sampled depth and with geologic age. The degree and effect of compaction, however, are much influenced by the lithofacies and tectonic history, The degree of strengthening with geologic age is the greatest in argillaceous rocks, greater in arenaceous rocks and less in pyroclastic rocks. Among six areas studied, there exists an interesting contrast in deformational behavior and strength. The rocks in Joban and Miura districts are much more ductile and weaker than rocks in the other areas. The confining pressure of ductile -to- visco-ductile transition and degree of strengthening with geologic age, too, suggest that very lower compressive stress has been applied on the rocks in Joban and Miura districts than in the other areas.

Determination of ultrasound scattering and intrinsic attenuations in heterogeneous media is of importance from material characterization to geophysical applications. Here, we present an efficient inverse method within a finite-size... more

Determination of ultrasound scattering and intrinsic attenuations in heterogeneous media is of importance from material characterization to geophysical applications. Here, we present an efficient inverse method within a finite-size scattering medium, where boundary reflection plays a crucial role. To fit the energy profile of scattered coda waves, we solve the acoustic radiative-transfer equation by Monte Carlo simulations for cylinder and slab geometries, under the isotropic scattering approximation. We show that the fit with the simplistic radiative-transfer solution in an infinite medium may result in underestimated values of the scattering mean free path, l s , and absorption, Q −1 i , by up to 40%. Our main finding is anomalous transport behavior in thin slab samples, where the ballistic peak and the diffusionlike one are merged into one single peak. This anomalous behavior, related to a wave-focusing effect in the forward direction, can mislead the inverse process and lead to an overestimation of l s by more than 200%. We compare simulated energy profiles with ultrasound envelopes obtained in a polycrystal-like granite slab from the ballistic to the diffusive regime. The l s deduced from off-axis detections agrees with that estimated from the correlation length of the shear-wave velocity by structural imaging analysis.

The effect of surface phenomena occurring at the interfaces between immiscible fluids and a solid on the seismic attributes of partially saturated rocks has not yet been fully studied. Meanwhile, over the past two decades considerable... more

The effect of surface phenomena occurring at the interfaces between immiscible fluids and a solid on the seismic attributes of partially saturated rocks has not yet been fully studied. Meanwhile, over the past two decades considerable progress has been made in the physics of wetting to understand effects such as contact line friction, contact line pinning, contact angle hysteresis, and equilibrium contact angle. In this paper, we developed a new rock physics model considering the aforementioned effects on seismic properties of the rock with a partially saturated plane-strain crack. We demonstrated that for small wave-induced stress perturbations, the contact line of the interface meniscus will remain pinned, while the meniscus will bulge and change its shape through the change of the contact angles. When the stress perturbation is larger than a critical value, the contact line will move with advancing or receding contact angle depending on the direction of contact line motion. A critical stress perturbation predicted by our model can be in the range of ß10 2 −10 4 Pa, that is typical for linear seismic waves. Our model predicts strong seismic attenuation in the case when the contact line is moving. When the contact line is pinned, the attenuation is negligibly small. Seismic attenuation is associated with the hysteresis of loading and unloading bulk moduli, predicted by our model. The hysteresis is large when the contact line is moving and negligibly small when the contact line is pinned. Furthermore, we demonstrate that the bulk modulus of the rock with a partially saturated crack depends also on the surface tension and on the contact angle hysteresis. These parameters are typically neglected during calculation of the effecting fluid moduli by applying different averaging techniques. We demonstrate that contact line friction may be a dominant seismic attenuation mechanism in the low frequency limit (<ß10 Hz) when capillary forces dominate over viscous forces during wave-induced two-phase fluid flow.

Changes in the sources of velocity anisotropy and their relative magnitude as maturation progresses in organic-rich shale are still incompletely characterized in the rock-physics literature. As a result of the increasing importance of... more

Changes in the sources of velocity anisotropy and their relative magnitude as maturation progresses in organic-rich shale are still incompletely characterized in the rock-physics literature. As a result of the increasing importance of organic-rich shale as unconventional reservoirs, a more thorough understanding of the elastic behavior of shale is needed. We have formulated a comprehensive, multiphysics, multiscale experimental methodology for the characterization of the intrinsic (syn-lithification) and extrinsic (postlithification) factors contributing to velocity anisotropy. Application of this methodology to unsatu-rated samples also enabled the characterization of the shale frame for fluid substitution modeling. The methodological framework was then tested on a set of five naturally matured organic-rich shale samples. In this experimental methodology, we combined classical rock-physics measurements, e.g., ultrasonic velocity and emergent high-resolution imaging techniques, such as X-ray diffraction (XRD), scanning electron microscopy, confocal laser scanning microscopy, and X-ray microtomography to better characterize the heterogeneous and microstructurally complex shale at all scales. The use of XRD-based lattice-preferred orientation measurements in conjunction with conventional ultrasonic velocity experiments confirmed that the degree of alignment of the mineral matrix governed the intrinsic anisotropy of organic-rich shale. The closure of soft, crack-like porosity, as identified from axial strain data, was identified as the extrinsic source governing the pressure sensitivity of velocity anisotropy. We determined, for the set of samples included in this study, that the intrinsic anisotropy was the dominant source of anisotropy at all confining pressures. Indeed, at low confining pressures, the opening of mi-crocracks contributed no more than 30% of the total velocity anisotropy. Applying these results to saturated rocks at depth indicated that, for these shales, the extrinsic, crack-based sources, will contribute no more than 30% of the shale anisotropy in situ.

Petrophysics and Rock physics modules are most widely used from last few decades for the precise measurement of reservoir characteristics Present study investigated the relationship between petrophysical and rock physics analysis in... more

Petrophysics and Rock physics modules are most widely used from last few decades for the precise measurement of reservoir characteristics Present study investigated the relationship between petrophysical and rock physics analysis in mapping detail reservoir properties. Eocene carbonate rocks are the focused zone including Sakesar and Chorgali Formations of current research study with the reference of hydrocarbon explorations. Rock Physics Parameters such as compressional velocity (Vp), shear wave (Vs), acoustic impedance (AI), Lambda-Rho (λρ), Mu-Rho (μρ), shear modulus (µ) and bulk modulus (k) whereas petrophysical properties including volume of shale (Vsh), porosities (density porosity, neutron porosity, sonic porosity, effective porosity), permeability, water saturations (Sw) and hydrocarbon saturations (Sh) have been calculated and constructed different cross-plots for the purpose of acquire accurate and desired information. Interpretations of Integrated rock physics and petrophysical modules of meyal-01 well reveal that Sakesar and Chorgali Formation having great capability to produce hydrocarbons. Resistivity logs show a good quality of hydrocarbon profiles at the depth of 3850 and 4050 m between Msfl, LLs and LLd. such interpretation is also supporting by cross-over effect between density and neutron logs. Sakesar and Chorgali Formation having 13 and 11 % shale content, 4 and 5 % effective porosity, 18 and 3 darcy permeability, 35 and 45 %, water saturations and 65 and 55 % and Hydrocarbon saturations respectively. Cross-plot between Rhob and Nphi logs recognized payable zone for hydrocarbon of Sakkesar and Chorgali Formations at the depth of 3850 and 4050 respectively. Such interpretations also supported by rock physics parameters i.e, compressional wave velocity Vp, poisson ratio elastic parameters such as Bulk modulus and shear modulus have greatly been reduced across the payable portion of Eocene reservoirs.

Shahbazpur structure is located in the southern Part of the central deep basin in the Hatia trough, where lie all the largest Gas fields of Bangladesh. A method is established to delineate the structural mapping precisely by interpreting... more

Shahbazpur structure is located in the southern Part of the central deep basin in the Hatia trough, where lie all the largest Gas fields of Bangladesh. A method is established to delineate the structural mapping precisely by interpreting four 2D seismic lines that are acquired over Shahbazpur structure. Moreover direct hydrocarbon indicators (DHI) related attributes are analyzed for further confirmation for presence of hydrocarbon. To do this synthetic seismogram generation, seismic to well tie, velocity modelling and depth conversion are performed. A limited number of seismic attributes functions that are available in an academic version of Petrel software are applied to analyze attributes. Seismic attribute analyses that are used in this interpretation mainly are associated to bright spot detection. Presence of bright spots or high amplitude anomaly over the present Shahbazpur structure, reservoir zone are observed. This signature will play a very important role in next well planning on the same structure to test the shallow accumulation of hydrocarbon. For better understanding of this shallow reserve, it is suggested to acquire 3D seismic data over Shahbazpur structure which will help to evaluate the hydrocarbon accumulation and to identify gas migration pathways.

Shear wave velocities (Vs), anisotropy, and shear wave splitting have been measured at pressures up to 600–800 MPa for ultrahigh-pressure (UHP) metamorphic rocks from the Dabie-Sulu orogenic belt, China, with a focus on three types of... more

Shear wave velocities (Vs), anisotropy, and shear wave splitting have been measured at pressures up to 600–800 MPa for ultrahigh-pressure (UHP) metamorphic rocks from the Dabie-Sulu orogenic belt, China, with a focus on three types of eclogites. Type 1 eclogites are coarse-grained, unaltered samples showing high densities and high Vs values (4.85 ± 0.06 km/s at 600 MPa); type 2 eclogites are fine-grained, sheared samples with intermediate Vs values (4.53 ± 0.04 km/s at 600 MPa); and type 3 eclogites are overprinted by amphibolite facies metamorphism and display low Vs values (4.33 ± 0.09 km/s at 600 MPa). The compositional layering and retrograde metamorphism can result in significant anisotropy and shear wave splitting in eclogites, suggesting their plausible contribution to seismic anisotropy in the lower crust, upper mantle, and particularly in subducted slabs. Integrating our P and S wave velocity results with reliable data from previous studies, we estimated the pressure and temperature derivatives of Vp, Vs, and Poisson's ratios for common rock types in the UHP metamorphic belt. The geometric means were used as a mixture rule to invert the lithological and chemical compositions of the layered crust from seismic refraction velocities. The inferred crustal composition suggests that the eclogite-bearing UHP rocks are tectonic slices of crust that have been thrust along a series of shear zones during the continental collision between the north China and Yangtze cratons, over a normal UHP-free middle lower crust with overall intermediate composition.

Synchrotron radiation X-ray tomographic microscopy is a nondestructive method providing ultra-high-resolution 3D digital images of rock microstructures. We describe this method and, to demonstrate its wide applicability, we present 3D... more

Synchrotron radiation X-ray tomographic microscopy is a nondestructive method providing ultra-high-resolution 3D digital images of rock microstructures. We describe this method and, to demonstrate its wide applicability, we present 3D images of very different rock types: Berea sandstone, Fontainebleau sandstone, dolomite, calcitic dolo-mite, and three-phase magmatic glasses. For some samples, full and partial saturation scenarios are considered using oil, water, and air. The rock images precisely reveal the 3D rock microstructure, the pore space morphology, and the interfaces between fluids saturating the same pore. We provide the raw image data sets as online supplementary material, along with laboratory data describing the rock properties. By making these data sets available to other research groups, we aim to stimulate work based on digital rock images of high quality and high resolution. We also discuss and suggest possible applications and research directions that can be pursued on the basis of our data.

We implement a technique to characterize the electromagnetic properties at frequencies 100 to 165 GHz (3 cm^-1 to 4.95 cm^-1) of oriented smectite samples using an open cavity resonator connected to a sub-millimeter wave VNA (Vector... more

We implement a technique to characterize the electromagnetic properties at frequencies 100 to 165 GHz (3 cm^-1 to 4.95 cm^-1) of oriented smectite samples using an open cavity resonator connected to a sub-millimeter wave VNA (Vector Network Analyzer). We measured dielectric constants perpendicular to the bedding plane on oriented Na^+ and Ca^++-ion stabilized smectite samples deposited on a glass slide at ambient laboratory conditions (room temperature and room light). The clay layer is much thinner (∼ 30 μm) than the glass substrate (∼ 2.18 mm). The real part of dielectric constant, ϵ_re, is essentially constant over this frequency range but is larger in Na^+- than in Ca^++-ion infused clay. The total electrical conductivity (associated with the imaginary part of dielectric constant, ϵ_im) of both samples increases monotonically at lower frequencies (< 110 GHz), but shows rapid increase for Na^+ ions in the regime > 110 GHz. The dispersion of the samples display a dependence ...

West Betara (WB) Field is located in South Sumatra Basin, Indonesia, tested hydrocarbon (Gas) from carbonate reservoirs of the Batu Raja Formation. This is an interesting challenge to describe the lateral distribution and its property... more

West Betara (WB) Field is located in South Sumatra Basin, Indonesia, tested hydrocarbon (Gas) from carbonate reservoirs of the Batu Raja Formation. This is an interesting challenge to describe the lateral distribution and its property within carbonate reservoir at minimum data information. The objectives of this study are to delineate carbonate reservoir distribution including the laterally rock properties by using seismic reservoir characterization methods. The availability of 3D seismic data, DST's data, conventional well data as wireline and mudlog data is very helpful in answering the challenge. By optimizing well data information, the sensitivity analysis can be generated from wireline log data to determine gas zone and appropriate seismic reservoir characterization method. 3D Seismic data provides a helpful inter-well information for determining and visualizing reservoir structure and rock properties at the present day, they also help us to generate seismic inversion model...

Frequency dispersion is a well-known effect in geophysics, which means that waves of different wavelengths propagate at different velocities. Amplitude dispersion is a less-known effect, which means that waves of different amplitudes... more

Frequency dispersion is a well-known effect in geophysics, which means that waves of different wavelengths propagate at different velocities. Amplitude dispersion is a less-known effect, which means that waves of different amplitudes propagate at different velocities. Herewith, we consider the alteration of the interfacial energy during wave-induced two-phase fluid flow in a partially saturated rock and demonstrate that this leads to a nonlinear amplitude dispersion effect. When the wave amplitude is small, seismic waves cause bending of the interface menisci between immiscible fluids at the pore scale. However, when the wave amplitude is sufficiently large, the interface menisci will slip at the pore scale, causing attenuation of the elastic energy by the contact line friction mechanism. At the zero frequency limit, all viscous dissipation models predict zero attenuation of the elastic wave energy, while this approach predicts a nonzero attenuation due to a static contact angle hysteresis effect. Herein, we extend the Gassmann's theory with three extra terms, which can be obtained from standard laboratory tests: pore-size distribution and interfacial tension between immiscible fluids and rock wettability (advancing and receding contact angles). We derive closed-form analytical expressions predicting the effective fluid modulus in partially saturated rock, which falls between Voigt and Reuss averages. Next, we demonstrate that the nonlinear amplitude dispersion effect leads to energy transfer between different frequencies. This may explain the low-frequency microtremor anomalies, frequently observed above hydrocarbon reservoirs, when the low-frequency energy of ocean waves (0.1-1 Hz) is converted to higher frequencies (2-6 Hz) by partially saturated reservoirs.

Fractures and faults in granitic rocks play an important role in geothermal systems because they permit the circulation of hot fluids. However, the thermo-hydro-mechanical behavior of granitic rocks has predominantly been studied at... more

Fractures and faults in granitic rocks play an important role in geothermal systems because they permit the circulation of hot fluids. However, the thermo-hydro-mechanical behavior of granitic rocks has predominantly been studied at temperatures exceeding 300°C but many geothermal systems experience temperatures much lower than this. The aim of this study was to evaluate how the depth, temperature, and amount and rate of mechanical loading associated conditions, that are realistic in low temperature geothermal system, influence the physical properties of geothermal reservoir hosting rock. We carried out both room temperature and low temperature thermo-mechanical tests on a granodiorite sample from the Liquiñe area, Chile, and performed post-experimental X-ray microtomography analysis to numerically estimate the permeability of the generated fractures. The results showed that both rock strength and rock stiffness decreased with increments of temperature treatment related to the development of thermal crack damage at temperatures > 150°C and through the development of sub-critical cracking at constant temperatures between 50-75°C. Slowest deformed samples also exhibited lower strengths, attributed to the development of sub-critical cracking. The cyclic triaxial loading test indicated that significant mechanical fracture damage was only initiated above 80% of the peak stress regardless of the number of repeated loading cycles at lower stresses. Low-temperature treatment appears to be a conditioning factor, but not the dominant factor in controlling the physical properties of reservoir hosting rocks. Our findings indicate that thermal crack damage is likely important for developing microfracture related permeability at depths between around 2-6 km where the temperature is sufficiently high to induce thermal cracking. At shallower depths, such was previously estimated the reservoir of Liquiñe, thermal crack damage is only generated adjacent to fractures that remain open and circulate the hot fluids but sub-critical cracking over time reduces the strength of rocks in lower temperature regimes. These processes combined to produce a geothermal reservoir in Liquiñe which likely first required the presence of a highly fractured fault zone.

A key task of exploration geophysics is to find relationships between seismic attributes (velocities and attenuation) and fluid properties (saturation and pore pressure). Experimental data suggest that at least three different factors... more

A key task of exploration geophysics is to find relationships between seismic attributes (velocities and attenuation) and fluid properties (saturation and pore pressure). Experimental data suggest that at least three different factors affect these relationships, which are not well explained by classical Gassmann, Biot, squirt-flow, mesoscopic-flow and gas dissolution/exsolution models. Some of these additional factors include (i) effect of wettability and surface tension between immiscible fluids, (ii) saturation history effects (drainage versus imbibition) and (iii) effects of wave amplitude and effective stress. We apply a new rock physics model to explain the role of all these additional factors on seismic properties of a partially saturated rock. The model is based on a well-known effect in surface chemistry: hysteresis of liquid bridges. This effect is taking place in cracks, which are partially saturated with two immiscible fluids. Using our model, we investigated (i) physical factors affecting empirical Brie correlation for effective bulk modulus of fluid, (ii) the role of liquids on seismic at-tenuation in the low frequency (static) limit, (iii) water-weakening effects and (iv) saturation history effects. Our model is applicable in the low frequency limit (seismic frequencies) when capillary forces dominate over viscous forces during wave-induced two-phase fluid flow. The model is relevant for the seismic characterization of immis-cible fluids with high contrast in compressibilities, that is, for shallow gas exploration and CO 2 monitoring.

The pivotal idea of this study is to unravel the processes that control heterogeneity in the attributes of the pore space in carbonate rocks (i.e. stiffness, connectivity and tortuosity), and, in turn, in the transport and elastic... more

The pivotal idea of this study is to unravel the processes that control heterogeneity in the attributes of the pore space in carbonate rocks (i.e. stiffness, connectivity and tortuosity), and, in turn, in the transport and elastic properties. We use starting rocks of variable fabric (i.e. a deposi-tional-dependent microstructure) to induce a specific process (e.g. chemical dissolution under stress) and then observe the development of the microstructure, permeability, porosity and velocity due to the induced chemomechanical processes. We find that the changes in the two end members of the analysed rock types (mudstones and packstones) can lead to two different evolutionary trends of permeability and velocity, depending on the effectiveness of dissolution with respect to compaction. The balance between the two depends on: (a) the fraction of the carbonate phases characterized by large surface area; and (b) the pore stiffness of the rock. Packstones are characterized by low pore stiffness and compact significantly upon dissolution. This behaviour leads to a decrease in velocity because of a reduction in the stiffness at the grain contacts and a slight increase in permeability. The latter is curbed by the ongoing compaction. Mudstones are characterized by higher pore stiffness, experiencing minimal or negligible compaction. This behaviour leads to a slight change in porosity and velocity. However, large permeability changes are observed, related to enhanced connectivity or decreased tortuosity of the pathways.

Campi Flegrei is an active, resurgent caldera that is located a few kilometres west of the city of Naples, a densely populated urban settlement in southern Italy. Identifying, locating at depth and better defining the geometry of the... more

Campi Flegrei is an active, resurgent caldera that is located a few kilometres west of the city of Naples, a densely populated urban settlement in southern Italy. Identifying, locating at depth and better defining the geometry of the magma feeding system of the caldera is highly relevant for assessing and monitoring its volcanic hazard. Based on a high resolution seismic reflection dataset, we investigated the deep structure of the volcano. Here we show that seismic wave amplitude variations with distance from the radiating source provide clear evidence for large amplitude seismic reflections from the top of an extended gas- and/or brine-bearing rock formation at about 3000 m and of an about 7500 m deep, low velocity layer, which is associated with a mid-crust, partial melting zone beneath the caldera. The modeling of magma properties based on measured seismic velocities indicates a relatively high melt percentage (in the range 80-90%). These new data suggest that a large magmatic sill is present well within the basement formations, which is possibly linked to the surface through a system of deep fractures bordering the caldera. The lateral extension and similar depth of the melt zone observed beneath the nearby Mt. Vesuvius support the hypothesis of a single continuous magma reservoir feeding both of these volcanoes.

Complex dielectric variations can address neatly the maturity of organic-rich mudrocks. We, therefore, apply an open hemispherical cavity resonator to measure complex dielectric permitivitties of five thin sections of oil (bakken)... more

Complex dielectric variations can address neatly the maturity of organic-rich mudrocks. We, therefore, apply an open hemispherical cavity resonator
to measure complex dielectric permitivitties of five thin sections of oil (bakken) shales (with different maturity) of sim\simsim 30 mu\mumum thickness
on glass-substrates around 2.15 mm thick in 100 - 165 GHz. The real part of complex dielectric permittivity ($\epsilon_{re}$) are constant but show significant
differences in magnitude based on maturity: (1) lowest, sim\simsim 1.9, for immature or early maturation stage, (2) higher than the immature one, sim\simsim 3.0 (also bundled up together),
for three oil-matured stages, and (3) highest, sim\simsim 4.9, for late or overmatured stage. The conductivity ($\sigma_{re}$) from imaginary part of the
complex dielectric constant ($\epsilon_{im}$) emphasizes two important features of conductivity of oil shales: (1) frequency dispersion,
and (2) maturity-dependence. We obtain increases of sigmare\sigma_{re}sigmare with maturity and frequency.