Shale Velocity Research Articles

Mechanical weakening behavior and energy evolution characteristics of shale with different bedding angles after microwave irradiation

Microwave irradiation, as a novel, clean, and efficient rock-breaking technology, can be employed in shale gas exploitation to address the challenges of low fracture efficiency and environmental pollution. Therefore, it is essential to investigate the physico-mechanical properties of shale under microwave irradiation. Firstly, samples with different bedding angles (0°, 30°, 60°, and 90°) were subjected to microwave irradiation at a power of 1 kW and frequency of 2.45 GHz for durations of 0, 20, 40, 60, and 80 s. Additionally, measurements of mass, P-wave velocity, and porosity were taken before and after microwave irradiation, followed by uniaxial compression testing using acoustic emission (AE). The results demonstrated that with increasing microwave irradiation duration, the P-wave velocity and mass of shale gradually decreased, exhibiting anisotropic behavior for the P-wave velocity. The highest degree of weakening (24.75%) was observed for shale at 0°, while the lowest (7.03%) occurred at 90°. Both uniaxial compressive strength and elastic modulus weakened gradually. Notably, USC displayed more significant weakening at 30° and 60°. The energy evolution pattern revealed increasing dissipated energy and decreasing brittleness index, enhancing anisotropy with duration, particularly at 60°. Moreover, AE captured the transition of failure mode from tensile splitting to tensile-shear failure. The results indicated the significant and anisotropic weakening effect of microwave irradiation on shale. The increase in porosity and permeability also provided preliminary evidence for the enhanced permeability ability of shale, resulting in reduced hydraulic fracturing pressures and decreased environmental pollution. Furthermore, the changes of most parameters revealed threshold effect of microwave irradiation duration, which can be classified as weak or strong depending on whether it occurs before or after 40 s. Therefore, attention should be paid to the threshold conditions of microwave irradiation duration to achieve efficient extraction. This research provided initial theoretical support for microwave-assisted shale gas exploitation.

The investigation of impact of temperature on mixed-mode fracture toughness of shale by semi-circular bend test

Unconventional oil and gas resources are important and have recently attracted attention. High temperature stimulation can effectively release the damage of water phase trapping, which was caused during the drilling and completion of hydraulic fracturing of shale gas reservoirs. The changes of physical and mechanical properties of shale under high temperature is of significance to the safety and efficiency of hydraulic fracturing. This study investigated the effect of temperature on seismic velocity, porosity, permeability, and mixed-mode fracture toughness of shale. Shale samples are separated into two groups, one group of 12 samples to test porosity, permeability and velocity, and the second group of 12 samples to test the fracture toughness of shale. The results showed that as the temperature increased, the color of the shale sample lightened, and seismic velocity decreased while the permeability and porosity increased. The results also revealed that as the temperature was raised to 400 °C–600 °C, seismic velocity, shale permeability, and porosity all increased. Furthermore, the mixed-mode fracture toughness was reduced, indicating that the threshold temperature of the shale was around 400 °C. The threshold value obtained can provide a basis for field evaluation and the potential application of high-temperature treatment. A numerical model was developed to simulate fracture propagation in SCB (semi-circular bend) samples subjected to thermal treatment. The numerical simulation agreed with the experimental results, indicating that the high temperature promoted fracture propagation and had a higher stress concentration at the fracture tip.

Wave velocity in shale in the Wufeng-Longmaxi formation in Sichuan Basin

Abstract Analyzing the pattern of wave velocity is important for velocity prediction and amplitude-versus-offset analysis during unconventional seismic exploration. Several parameters, including the maturity and microstructure of organic matter (OM), the wave velocity, the mineral composition and the density of shale from Upper Ordovician Wufeng and Lower Silurian Longmaxi, formations were experimentally evaluated in this study. To investigate the factors influencing the wave velocity, the obtained data were analyzed together with numerical calculations and previous experimental results. A theoretical model of an anisotropic differential equivalent medium (DEM) was then established and the following conclusions were drawn: (i) different from Bakken shale, OM in the Wufeng-Longmaxi (WL) shale is over-mature and patchy, with higher elastic parameters for the kerogen; (ii) different from other areas, the amount of kerogen (being over-mature) in WL shale is not correlated with the wave velocity; (iii) bogenic quartz minerals were abundant in the tested samples, and their amount was positively correlated with OM, whereas OM was negatively correlated with the amount of clay; (iv) clay, quartz and kerogen contents had different association with the rock skeleton, resulting in a V-shaped relationship between the quartz content and wave impedance, with the slope of the growing branch being higher than that of the decreasing branch and (v) the anisotropic DEM model effectively proves the influence of OM maturity and patch shape on shale velocity. Also, the V-shaped relationship between quartz and wave impedance caused by skeleton change are verified. This study provides valuable data as well as a theoretical basis for seismic interpretations in the study area.

Seismic Imaging of a Shale Landscape Under Compression Shows Limited Influence of Topography‐Induced Fracturing

AbstractWe used seismic refraction to image the P‐wave velocity structure of a shale watershed experiencing regional compression in the Valley and Ridge Province (USA). From estimates showing strong compressional stress, we expected the depth to unweathered bedrock to mirror the hill‐valley‐hill topography (“bowtie pattern”) by analogy to seismic velocity patterns in crystalline bedrock in the North American Piedmont that also experience compression. Previous researchers used failure potentials calculated for strong compression in the Piedmont to suggest fractures are open deeper under hills than valleys to explain the “bowtie” pattern. Seismic images of the shale watershed, however, show little evidence of such a “bowtie.” Instead, they are consistent with weak (not strong) compression. This contradiction could be explained by the greater importance of infiltration‐driven weathering than fracturing in determining seismic velocities in shale compared to crystalline bedrock, or to local perturbations of the regional stress field due to lithology or structures.

Sand injectite mapping using a resistivity-velocity transform function

Lack of resolution in the distribution of sand injectites in hydrocarbon fields is common and makes it difficult to predict drilling challenges and plan for optimum production. A practical workflow was developed that enables the distinction of shale and sand bodies by using a combination of low-resolution seismic data and high-resolution resistivity log data. Measured resistivity logs were used to predict synthetic velocity logs, which accurately match shale velocities and over- or underestimate velocities of other rock types. The synthetic velocity logs were spatially distributed in a 3D cube in order to predict synthetic velocities in between and away from the well locations. The 3D cube was representative of a field. It covered the interval from the seabed to below the reservoir. The spatial distribution was based on a geostatistical approach guided by measured seismic interval velocities. A residual velocity cube was calculated from the measured and synthetic velocities. The residual velocity cube produced near-zero velocities for shaly materials and velocity over- or underestimates for other rock types. Interpretation of the residual velocity cube required the identification of strong stratigraphic markers. The markers were removed from the residual cube by setting their specific layer velocities to 0 m/s. The final information stored in the residual velocity cube was then related to the over- or underestimated velocities in sand bodies.

Effect of loading rate on fracture behaviors of shale under mode I loading

In this study, the effect of loading rate on shale fracture behaviors was investigated under dynamic and static loading conditions. Cracked straight through Brazilian disc (CSTBD) shale specimens were tested with a split Hopkinson pressure bar (SHPB) setup and INSTRON1346 servo-testing machine under pure mode I loading conditions. During the test, the crack propagation process was recorded by high-speed (HS) camera, and the acoustic emission (AE) signal generated by the fracture was collected by acoustic emission (AE) system. At the same time, crack propagation gauge (CPG) was used to measure the crack propagation velocity of the specimen. The results show that the crack propagation velocity and fracture toughness of shale have a positive correlation with the loading rate. The relationship among the crack propagation velocity, the fracture toughness and the loading rate is established under the static loading condition. In addition, the characteristics of AE signals with different loading rates are analyzed. It is found that the AE signals generated by microcrack growth decrease with the increase of loading rates. Meanwhile, the turning point of cumulative counting moves forward as the loading rate increases, which shows that the AE signal generated by shale fracture at low loading rate mainly comes from the initiation and propagation of microcracks, while at high loading rate it mainly comes from the formation of macro large-scale cracks. The fracture mechanism that causes shale fracture toughness and crack propagation velocity to vary with loading rate is also discussed based on the analysis results of AE signals.

Determining Fracture Pressure Gradients from Well Logs

Fracture pressure gradient is one of the essential parameters used in determining mud weight profiles during drilling operations. We have determined fracture pressure gradients from well logs obtained from three producing wells in Onshore Niger Delta using an empirical model. Key logs needed for the prediction were conditioned and quality controlled to meet the standard required for reliable results. The true vertical stress, normal compaction trend and compressional shale velocity trends were generated from the logs (density and sonic logs). Poison’s ratio was obtained from compressional and shear wave velocities derived from sonic log. Pore pressures in the three wells were then predicted using Eaton’s Method. The predicted pore pressures, overburden pressures and poison’s ratio were used to determine fracture pressures using Ben Eaton’s Model. Results showed that there is a suitable drilling margin at all depths only in well G-005. Drilling well A-001 to a depth of 10962.81 ft and K-001 to a depth of 12626.9 ft will fracture the formations because the fluid pressures at those depths approximate the fracture pressures of 8536.7psi and 9506 psi with corresponding gradients of 0.78 psi/ft and 0.75 psi/ft respectively. The implication is that drilling deeper in the field will results in very low seal capacity magnitudes, thereby presenting a higher risk of top-seal failure.

Velocity anisotropy analysis for shale lithology of the complex geological section in Jaisalmer sub-basin, India

Measurement of velocity anisotropy is an essential parameter for capturing the heterogeneity of sub-surface geology to characterise the hydrocarbon-bearing reservoir. The incorporation of velocity anisotropy parameters during the preparation of the 3D velocity model represents a robust result in a challenging geological set-up during interpretation. Generally, we can observe that the shale formation is more sensitive to velocity anisotropy response in comparison with other formations such as sandstone, siltstone for clastic reservoir or limestone and dolomite for carbonate reservoir. This study was performed mostly in the high amount shale section mixed with limestone and claystone of the Jaisalmer sub-basin area which lies in the western part of India. The preparation of the velocity model for frequent changes of lithology in the clastic and carbonate reservoir is challenging due to several changes of velocity which show a limitation in the result of the gridded velocity model. The objective of this study is to capture the changes of compressional and shear wave velocity in mixed lithology of the significant shale formation. The idea was due to the inclusion of the anisotropy incorporated changed velocity during the preparation of the gridded velocity model for correctly identified lithology. The shale formation which is the zone of investigation of the current study is situated over a carbonate sequence, and an estimated velocity anisotropy factor of this shale formation will contribute significantly during the cumulative study of velocity modelling of all formation. The current study shows that shale formation shows the character of orthorhombic anisotropy; however, this study was performed based on significant changes of well log data and related effects of vertically transverse isotropic parameters of the shale formation. The fundamental Thomsen anisotropy parameters were estimated by capturing the deviation of five independent stiffness coefficients. Significant changes in evaluated shale velocity were observed after the incorporation of the estimated Thomsen parameter in velocity values.

Elastic characteristics of overpressure due to smectite-to-illite transition based on micromechanism analysis

Characterizing the elastic signatures of overpressure of shale caused by the smectite-to-illite transition relies on a good understanding of this mechanism and is also necessary for pore-pressure prediction. Methods of pore-pressure prediction in shales that have undergone smectite-to-illite transition are mostly based on empirical fitting without a quantitative interpretation based on a micromechanism analysis. With upscaled wireline-logging data, two trends of smectite-to-illite transition are categorized by using the crossplot of sonic traveltime and density. Trend I associated with a fluid-expansion scenario exhibits a decrease of sonic velocity with little change in the bulk density, whereas trend II induced by a fluid-loss scenario contains an increase of density with little change in the sonic velocity. The fluid expansion typically gives rise to high-magnitude overpressure and tends to happen when the overlying formations have more shaly contents and low permeability. The fluid loss case tends to have relatively deeper overpressure onsets, and its overlying formations tend to have more sandy contents with relatively high permeability. We develop a modeling framework to capture the elastic and pore-pressure evolution characteristics in shale during the smectite-to-illite transition. With proper bulk volume models, the velocity, density, and pore pressure increase of shale can be computed in the fluid expansion, fluid loss, and a mixture of these two scenarios. After calibration with logging data, rock-physics modeling can quantitatively interpret the rock-property evolution characteristics within the smectite-to-illite transition zone.

Experimental Investigation on Mechanical and Acoustic Parameters of Different Depth Shale Under The Effect of Confining Pressure

Investigations on the effects of confining pressure and burial depth on mechanical and acoustic parameters are significant for studying the deep shale deformation, failure rule, and hydraulic fracturing. Shale specimens at six different depth levels ranging from 1535 to 1635 m have been collected from a shale gas well in southwest China. RTR-1000 rapid rock triaxial testing system has been applied to carry out the mechanical and acoustic experiments with 19 shale specimens. The experimental results revealed that the peak deviatoric stress, peak axial strain, peak volumetric strain, residual stress, and axial wave velocity are directly proportional to confining pressure and burial depth, whereas elastic modulus is not affected much by both confining pressure and burial depth and the Poisson ratio decreases with the increase of confining pressure. In the burial depth range 1535–1635 m, the variation of Poisson’s ratio is not obvious with the depth changes, and their relationship has high randomicity. The Wave velocity Anisotropy of tested shale is greatly affected by the degree of stratification development rather than the corresponding crustal stress. The coefficient of variation and the degree of stratification development are inversely proportional to burial depth. The axial wave velocity of shale is closely related to the loading process. In the compaction stage, wave velocity increases rapidly with the increase of strain. And in the elastic yielding stage, wave velocity increases slowly along with the strain build-up. This study will help to deepen the understanding of the physical and mechanical properties of Wuxi shale and guide the shale gas exploitation in China.

Thermal effective stress in shales

Calculating velocities in shales in thermal production settings is important to refine time-lapse reservoir characterization from seismic. The effective stress concept is attractive to potentially reduce the amount of expensive core calibration data required. We propose a formulation for thermal effective stress in shales based on the idea of balancing undrained pore pressure increments from thermal expansion with an increase in the matrix stress to minimize pore deformation. This formulation is motivated by a desire to simplify forward modeling, reduce the number of dimensions that must be experimentally calibrated through core testing, and to leverage existing velocity-stress relations for thermal applications. The concept was tested on data from a well-known set of experiments consisting of two North Sea Kimmeridge shale core samples, which displayed a linear dependence of velocity on pressure and temperature. These data were found to be consistent with the proposed thermal effective stress model with a constant effective stress coefficient when considering elastic changes but do not prove that the concept is universally valid. Thermal effective stress coefficients were calculated for P- and S-wave velocities from the data and were found to lie from 0.66 to 1.22, demonstrating reasonable scaling for the proposed model.

A rock physics model for characterizing the total porosity and velocity of shale: A case study in Fuling area, China

Abstract The total porosity in a shale gas reservoir is the key parameter to evaluate its potential production capability. Petroleum geologists have been pursuing an accurate way of predicting total porosity in shale gas reservoirs from logging curves. In the Fuling area near Chongqing in China, we use core test data and well logging data, in order to establish a logging response model for porosity. Through the analysis of the data, we found that the porosity and the P-sonic (P-velocity) have a strong correlation. By combining our results with previous research (i.e., physical rock data), we establish a new model which better predicts the total porosity of a given a shale reservoir than the models established in previous research. In addition to total porosity, mineral composition, pore pressure, pore fluid-type, and confining pressure affect P-velocity. By taking a series of artificial cores as test objects and systematic analysis of total porosity, mineral composition and content, pore fluid-type and pressure on the P-velocity, we establish response templates between every individual parameter and P-velocity. To this end, we further establish a multi-parameter rock physical characterization equation for the total porosity and P-velocity, and analyze its applicable conditions. Using the rich geological and geophysical data of the Lower Silurian Series in the Fuling area, we gradually improve the model for the total porosity and verify the results using well logging data. Finally, a set of accurate methods are established to predict the total porosity in shale gas reservoirs by using well logging data.

Disequilibrium compaction overpressure in shales of the Bavarian Foreland Molasse Basin: Results and geographical distribution from velocity-based analyses

Abstract Shale velocity data from sonic logs and vertical seismic profiles, drilling data and in situ pressure measurements from a total of 116 wells have been analyzed to gain an improved understanding of the lateral and vertical distribution and formation of overpressure in the Bavarian Foreland Molasse Basin. Pore pressure from sonic and vertical seismic profile velocities has been analyzed by establishing a normal compaction trend for Cenozoic and Mesozoic shales combined with a classical Eaton approach. The study demonstrates that a single shale normal compaction trend for the Bavarian Foreland Molasse Basin is sufficient to estimate pore pressure and thus overpressure from sonic and vertical seismic profile velocity. Maximum overpressure develops at depths between 1500 and 2500 m and increases with depth at a constant effective stress of 20 MPa. The strong dependency of overpressure on burial depth, constant effective stress and restriction to shale units that are overlain by sequences with very high sedimentation rates indicates that disequilibrium compaction is the main cause for overpressure. Also, variable presence of Cretaceous shales is a key control of overpressure occurrence in Oligocene shales in the Bavarian Foreland Molasse Basin, since Cretaceous shales likely act as a “pressure buffer” to underpressured Mesozoic carbonates. Successful detection and prediction of overpressure from vertical seismic profile data is encouraging for future pre-drill prediction of overpressure from velocity data of seismic surveys in the Bavarian Foreland Molasse Basin, resulting in improved well planning, reliable calculation of project costs, and improved safety during drilling activities in the Bavarian Foreland Molasse Basin. The presented overpressure distributions will be a key input for future geomechanical, basin and reservoir modelling studies in the Bavarian Foreland Molasse Basin.

Model-based pore-pressure prediction in shales: An example from the Gulf of Mexico, North America

Accurate pore-pressure interpretation and prediction play important roles in understanding the sedimentary history of a basin and in reducing drilling hazards during hydrocarbon exploitation. Unlike typical reservoir rocks, in which pore pressures can be directly measured, pore pressures in shale must be inferred via their state of compaction. We have used the shale acoustic properties to accomplish this. Shale P- and S-wave velocities were first calculated using an anisotropic differential effective medium model. This model was built using elastic properties of wet clay mineralogy, and the total porosity of the shale was obtained from basic open-hole well-log measurements. These simulated shale velocities were systematically higher than sonic velocities observed on a test data set from a Gulf of Mexico well, penetrating a 1200 m vertical section of overpressured shale. The difference between the modeled velocities and the sonic measurements was then evaluated to estimate the abnormal pore pressure based on an exponential relationship between the pore pressure and the ratio of measured to modeled velocity. Using a reasonable exponent, the predicted pore pressure was shown to be in good agreement with direct pore-pressure measurements either made in adjacent sand layers that are thought to be in pressure equilibrium with the shales or inferred from drilling mud weights.

Effect of bedding planes on wave velocity and AE characteristics of the Longmaxi shale in China

The experimental work described in this paper was carried out in order to discover more about the effects of bedding planes on wave velocity and acoustic emission (AE) characteristics of shale. Two groups of specimens, which were collected from the Longmaxi shale outcrop in Chongqing, China and cored perpendicular and parallel to the bedding planes, were tested under uniaxial compression, and the wave velocity and AE were monitored. There were obvious differences in the acoustic characteristics of shale with different bedding plane orientations. The experimental results show that (1) the average increasing rates of P- and S-wave velocities were 39.86 and 54.41%, respectively, for the specimen with a load perpendicular to the bedding planes (Y-0). The P-wave velocity and axial strain of specimen show a marked logarithmic relationship. However, the average increasing rates of P- and S-wave velocities were 5.44 and 10.54%, respectively, for the specimen with a load parallel to the bedding planes (Y-90). The good linear relationship between P-wave velocity and axial strain before failure of specimen has been built. Generally, S-wave velocity was more sensitive to axial strain than P-wave velocity. (2) AE characteristics for Y-0 showed that a few signals → quiet period → stable increase → steep increase; for Y-90: quiet period → stable increase → sudden increase → sharp increase. The AE energy for two groups of specimens was concentrated on low and middle of amplitudes (45-80 dB), but the proportion of amplitudes (80–100 dB) and the total counts of AE for Y-0 was 1.95, 2.2 times as much as that for Y-90, respectively. The results preliminarily revealed the effect of bedding orientation on the wave velocity and AE properties of shale and may provide guidance for the improvement of acoustic logging and microseismic monitoring in the field.

Experimental investigation of factors affecting compressional and shear wave velocities in shale and limestone of Ewekoro formation of Southern Nigeria sedimentary basin

Compressional V p and shear V s velocities measurements were taken out on fluid-saturated shale and limestone obtained from the Ewekoro quarry of Southern Nigeria sedimentary basin at constant differential pressure of 50 MPa with porosities ranging from 0.32 to 0.53% and 0.01 to 0.35 for limestone and shale, respectively, while the volume of clay content C ranges from 0 to 60% and 0 to 40% for limestone and shale, respectively. Correlation coefficient for the velocities of both clean samples and those with clay minerals ranged from 0.972 to 1.000 and 0.971 to 1.000, respectively, with limestone having the lesser for both. A very small amount of clay, about 0.21 and 0.23, reduced the elastic modulus of limestone and shale, respectively. For water-saturated shaly samples, V s was more sensitive to porosity and clay content than V p . Consequently, velocity ratios V p /V s also showed a reasonable degree of correlations with clay content and porosity. For both limestone and shale studied, the presence of porosity is the most important parameter in reducing velocities followed by clay content due to the softening of its matrix. This study established that wave velocities are functions of porosity and clay content of porous shale and limestone of Ewekoro formations.

Temperature-dependent thermophysical properties of Ganurgarh shales from Bhander group, India

Thermal conductivity is a very important property of rocks which determines the rate of heat transfer between two adjacent layers of rock. Temperature-dependent thermal properties of Ganurgarh shale are analyzed and presented over a temperature range from air dried to 900 °C. Physico-mechanical properties, porosity, density and P-wave velocity are determined as per ISRM standards. In addition, changes in internal microstructure are studied using scanning electron microscopy (SEM). Thermal conductivity is predicted using P-wave velocity and porosity of Ganurgarh shale. The effect of temperature on the microstructure, porosity, and mineralogical composition of shale and dependency of thermal conductivity on porosity of shale is discussed. It has also been found that as temperature increases, porosity of Ganurgarh shale increases up to 2.3 times of its initial porosity because of thermal cracking which also acts as barrier of heat flow and hence thermal conductivity decreases. Uncertainties of measured quantities are calculated and the total combined expanded uncertainty for thermal conductivity value of Ganurgarh shale at 95 % confidence level is less than 6 %. All the results obtained using a state-of-the-art single hot guarded parallel plate apparatus.

Study of temperature effect on thermal conductivity of Jhiri shale from Upper Vindhyan, India

Shale is a very important sedimentary rock that is used as building construction material and found predominantly underground. Shales have been found to contain both oil and gas, which can be extracted only when it is fractured. In this paper, temperature dependent thermal properties of Jhiri shale are presented over a temperature range from air-dried to 900 °C. Porosity, density, and compressional wave velocity measurement have been done as per ISRM standard. Furthermore, internal microstructure is studied using scanning electron microscopy (SEM). In this study, thermal conductivity is predicted using P-wave velocity and porosity of Jhiri shale. The effect of temperature on microstructure, porosity, and mineralogical composition and dependency of thermal conductivity on porosity is discussed. It was found that as temperature increases, porosity of Jhiri shale also increases because of thermal cracking, which acts as a barrier of heat flow, reducing thermal conductivity. Uncertainties of measured quantities are calculated and the total combined expanded uncertainty for thermal conductivity value at 95 % confidence level have been found to be less than 6 %.

Prediction of sonic velocities in shale from porosity and clay fraction obtained from logs — A North Sea well case study

Prediction of sonic velocities in shales from well logs is important for seismic to log ties if the sonic log is absent for a shaly section, for pore pressure anomaly detection, and for data quality control. An anisotropic differential effective medium (DEM) was used to simulate elastic properties of shales from elastic properties and volume fractions of silt and wet clay (a hypothetical composite material that includes all clay minerals and water). Anisotropic elastic coefficients of the wet clay were assumed as a first-order approximation to be linearly dependent on wet clay porosity (WCP). Here, by WCP we mean a ratio of a pore volume occupied by water to a total volume of the wet clay. Effects of silt inclusions on elastic coefficients of shales were taken into account by using the anisotropic differential effective medium model. Silt inclusions were modeled as spherical quartz particles. Simulated elastic coefficients of shales were used to calculate compressional and shear velocities, and these were in a good agreement with the sonic velocities observed on a test data set from an offshore Mid-Norway well penetrating a 500-m vertical section of shale. To further study the elastic properties of wet clays, elastic coefficients calculated from compressional and sonic velocities measured in shales were inverted for vertical profiles of wet clay elastic coefficients. Analysis of these coefficients found that in the well considered, the increase in elastic coefficients of shales was controlled by the increase of silt fraction with depth. Elastic coefficients of wet clay found no increase with depth. The inverted elastic moduli of wet clay found much stronger correlation with WCP than do the moduli of shale. This confirmed the hypothesis that silt fraction is one of the key parameters for the modeling of elastic properties of shale.

Linking rock physics and basin history — Filling gaps between wells in frontier basins

A method has been developed to link present-day well or seismic measurements through rock-physics temperature and net-erosion variations caused by past tectonic events within a sedimentary basin. An ambiguous and intricate link among physical rock properties, temperature history, and burial history is demonstrated by modeling examples. Net-erosion estimates presuppose an estimate about temperature history and vice versa. Net erosion and temperature history normally cannot be estimated independently when using elastic rock properties, although net erosion in principle can be estimated independently of temperature for shallow unconsolidated sediments. For rocks that have been subjected to thermal diagenesis, either net erosion or paleotemperature must be known by consensus while estimating the other, or both must be estimated simultaneously. Well data demonstrate how rock physics is used to predict the maximum historical temperature and net erosion based on well-log velocities. From these parameters, sediment cooling can be derived. These estimates can be performed away from well positions, based on seismic velocities in shale. Temperature and erosion estimates are given for a 2D line, and large lateral variations are estimated. Normally, if well data are sparse, there will be a high uncertainty in net-erosion estimates. The new method reduces uncertainty in net-erosion and temperature estimates in areas away from well control. The method is used in an area with good estimations of uplift and erosion from wells and gives results consistent with observations.