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Abstract: Based on petrophysical, magnetic, gravity, electric, seismic and drilling data, combined with geological regularities, this paper proposed an integrated approach for the distribution prediction and lithology recognition of volcanic rocks, as well as the exploration prospect and target optimization of hydrocarbon deposits. The exploration technology was improved in the application to exploration in the Ludong-Wucaiwan area in Junggar Basin. Some important viewpoints are concluded as follows: aeromagnetic anomaly gradient belts correspond to volcanic faults, faults control the distribution of volcanic rocks and accordingly their local structures, aeromagnetic anomaly gradient belts correspond to highly-developed fracture zones and are prospective areas for volcanic reservoirs. The proposed integrated approach is proven effective by the exploration drilling results with high-flow gas wells. [Copyright &y& Elsevier]

The founder of the Russian school of direct interpretation of potential fields (with minimal prior geological-geophysical information) was V.M. Berezkin, who introduced the operator of total normalized gradient for the 2D interpretation of profile gravity data sets. This operator was successfully applied in searches of hydrocarbon reservoirs. The further development of this approach (the so-called quasi-singular points method) has allowed solution also to various structural problems, using mathematical criteria for the transition from extremes of total normalized gradient fields to coordinates of anomalous sources. The main numerical evaluation strategy is based on stabilized downward continuation of field derivatives and specific use of the filtration properties of Fourier series approximation. The characteristic properties of the quasi-singular points method are: 1) presentation of a more general total normalized gradient function through additional parameters (derivative order m, form of smoothing function Q, number of Fourier coefficients N* with maximal N), optimum values being chosen during a peak-spectrum analysis of the interpreted function; 2) calculation of the set of total normalized gradient fields for various values of N*/ N, representing coordinate systems { x, N*/ N} as an ‘axes tree’ of extrema, where each 2D total normalized gradient field is representationally compressed in a 1D line, permitting a) immediate overview of the positions of the axes in all variants of the calculated fields and b) reduction of the retained information, as required in subsequent interpretation; 3) development of two criteria for transition from extrema of total normalized gradient fields to the coordinates of anomaly sources. The quasi-singular points method is intended for tracing limiting gently-sloping boundaries, if their micro-relief features are sources of the interpreted anomaly but sub-vertical contacts may also be traced. The method has been tested in delineating various geological structures. One of the most challenging, successfully achieved, was tracing of the Moho discontinuity and study of the upper mantle, using only Bouguer anomaly data along interpretation profiles. This is attested in an example of two regional profiles intersecting the European part of Russia. The central part of one of them coincides with the results from a deep seismic profile. [ABSTRACT FROM AUTHOR]

Abstract: In the use of thermoluminescence (TL) and optically stimulated luminescence (OSL) for dosimetry and for geological and archaeological dating, the nature of the dose dependence of the luminescence signal is of great importance. Non-linear dependence has been shown to result either from non-linear filling of the relevant traps or recombination centers during excitation, or by a combined effect of the linear filling of traps and centers due to processes taking place during the read-out stage. Sublinearity, which had been found in several materials, was usually attributed to saturation effects during excitation of either the relevant traps or centers. Sometimes, the competition effects during the excitation between traps result in superlinearity of some TL peaks and sublinearity of others. In the present work, we show that sublinear dose dependence may take place even in the simplest possible case of one trap–one recombination center (OTOR), even when the traps and centers are far from saturation. Analytical derivations as well as simulations consisting of the numerical solution of the relevant sets of coupled differential equations show the occurrence of the sublinear dose dependence under these circumstances. The filling of the traps is shown to behave like D 1/2 where D is the excitation dose, for an appropriate choice of the trapping parameters. This, in turn, may result in a similar dose dependence of the TL and OSL signals. [Copyright &y& Elsevier]

Abstract: This article demonstrates that violet (405nm) stimulated luminescence (VSL) signal from quartz contains contribution from deep traps that are otherwise not accessible with blue light (470nm). Additionally, it also contains the typical fast and slow components observed with the blue light stimulation. Although, the fast OSL component is measured with similar efficiency by blue and violet lights, the slower OSL components (especially S 3) are measured relatively more efficiently with the latter. New insight into the origins of quartz luminescence is presented through a comparison of violet and blue lights stimulation, and thermal stimulations. Finally, it is shown that the deep traps probed through violet light stimulation have potential for increasing the dose measurement/dating range using quartz. The post-blue VSL signal allows easy, precise measurement of dose up to at least 1kGy in our samples, while the initial BSL signal shows saturation at ∼100Gy. The violet stimulation provides a means for optically probing the traps that give rise to signals with extended growth (dose-response) characteristics such as high temperature isothermal TL (ITL), the slow component OSL, and perhaps also the thermally transferred-OSL (TT-OSL). [Copyright &y& Elsevier]

Methods for predicting the permeability and elastic properties of hydrocarbon reservoirs containing natural fractures are important for the production optimization and seismic characterization of fractured reservoirs. Effective medium theories may be used for this purpose but need to be validated using numerical calculations of the fluid flow and seismic properties for realistic fracture networks. The prediction of effective permeability and elastic properties using effective medium theories of fractured media are compared with numerical simulations using a discrete fracture network (DFN) containing two sets of non-orthogonal vertical fractures. Discrepancies between the permeability obtained from the simulations and using effective medium theory are attributed to an oversimplified treatment of fracture interconnectivity in the effective medium theory used. The simulations indicate that the effect of interconnectivity on fluid flow varies with stress and flow direction. By contrast, the effective elastic compliances obtained from numerical simulation and effective medium theory are in good agreement, even for relatively complicated fracture networks. Although permeability and seismic anisotropy both vary with stress, the relation between them is not simple. The variation in reflection amplitude with offset and azimuth is found to be sensitive to the ratio of the normal to shear compliance of the fractures, whereas permeability is less sensitive to this ratio. For the DFN studied, the permeability rapidly increases at high level of stress due to dilation of the fractures when the in situ stress field is strongly anisotropic. [ABSTRACT FROM AUTHOR]

The properties of hydrocarbon reservoirs are generally derived from core experiments and use theories of fluid flow that normally assume homogeneous core properties. Reservoirs, however, are generally heterogeneous, and interpretations of the results of these experiments are likely to be unreliable if the core from which the data are derived is heterogeneous. This article examines experimentally immiscible displacement through well-defined permeability heterogeneities, modeled using 2-D visual models packed with clear beads of different permeabilities. The results indicated that the displacement patterns were dominated by capillary pressure effects and that they were different from those found in miscible systems. This understanding is needed, since in reservoir simulators, the simulator codes must contain the correct physics, and in core analysis, the effluent profiles must be correctly interpreted for sensible predictions. [ABSTRACT FROM AUTHOR]

Abstract: A simple experiment for capillary sealed trap shows that leakage would occur only from the weakest point in the trap. As an extens ion of this concept, the sequestrated and accumulated CO2 in the structural high may happen to leak from the unexpected weak point near the top of sealing layer. On the other hand, if CO2 were sequestrated into the flank of tilted aquifer, CO2 in separate phas e would migrate upward within aquifer with no CO2 leakage into the sealing layer above and leaving some residual amount behind. According to this concept, the best location for sequestration of CO2 could be the flank of the structure rather than the top. [Copyright &y& Elsevier]

Abstract: Deep-sea basalt aquifers have been identified for geological CO2 sequestration in worldwide locations and offer vast reservoir capacities, permanent geochemical trapping potential, and other deep-sea protections that significantly reduce the risk of post- injection leakage. Using site-specific criteria, we target basalt aquifers along seismic and aseismic oceanic ridges, and calculate the injection volume potential for each. Results indicate that these aquifers occur in many oceans and could sequester 2.3–11.5 Tt-C along seismic ridges and 5.9–29.6 Tt-C along aseismic ridges. The enormous size of these potential reservoirs warrants further research and pilot experiments in each geographic setting. [Copyright &y& Elsevier]

Abstract: Gravitational trapping of carbon dioxide in deep ocean sediments is attractive both for the long term stability provided by gravity as well as the large volume and hence storage capacity of deep ocean sediments at necessary depths. Unfortunately, most pelagic sediments suffer from extremely low permeability and are not expected to have an overlying mechanical seal, making emplacement of CO2 contingent upon large scale hydraulic fracturing and some mechanism of arresting fracture growth before reaching the seafloor. An experimental design is presented with the capability of testing a variety of proposed fracture arrest mechanisms. [Copyright &y& Elsevier]

Abstract: Previous research suggests that for many geological CO2 sequestration reservoirs, up to 60% of the injected CO2 will be trapped by capillary forces (irreducible saturation), a mechanism termed residual CO2 trapping. More specifically, our recent models of ongoing field tests of geological sequestration suggest that residual CO 2 trapping can be maximized if the CO2 plume rises a greater distance due to buoyancy (i.e., injection at the deepest part of a thick reservoir) and sweeps a larger area before coming in contact with low permeability caprock. Although this strategy maximizes the residual CO2 trapping in theory because CO2 plume contacts more pore spaces, it also increases the probability that upwelling- CO2 may come into contact with faults or other leakage pathways. Geological heterogeneity seems to play greater role with respect to residual CO2 trapping potential. To help clarify what processes and properties will maximize residual CO2 trapping and minimize CO2-buoyant flow, we conducted a systematic analysis of permeability () fields and its correlation structures. The fields served as primary parameterization of a numerical model describing CO2 migration during a 100-year simulation period. We compared various permutations of two-dimensional conceptual models, including homogeneous, random, homogenous with low- lens, and anisotropically-correlated fields. Using a Sequential Gaussian Simulation method, for most of models, we generated 10 realizations in each model permutation. In each simulation, the amount of mobile-, residual-, and aqueous-trapped CO2 was calculated and the spatial distribution of the CO2 plume was quantified using the first and second spatial moments. Both homogeneous and random simulation results suggest that the amount of residual trapped CO2 increases as the effective increases. These results imply that the overall velocity distribution, which governs the sweeping area of the CO2 plume, is a critical factor for residual CO2 trapping. However, as overall velocity (or field) increases, we observed that the CO2 plume reaches the caprock more quickly. In simulations of anisotropically correlated fields with specific correlation length ratios of 25 m×10 m,50 m×10 m, and 100 m×10 m in x (horizontal) and z (vertical) directions, respectively, the CO2 migration distance due to buoyancy force is shorter as the horizontal correlation length becomes greater. In addition, as the horizontal correlation length becomes greater, residual trapping increases because the CO2 plume spreads farther laterally, sweeping a larger area. In sum, results of this analysis suggest that heterogeneous fields with greater anisotropic correlation ratios tend to maximize residual trapping and minimize buoyancy-driven CO2 migration. Our findings also suggest that correlation structures, especially anisotropic media with specific ratios of correlation lengths, can strongly impact CO2 trapping mechanisms by controlling velocity and tortuosity, which in turn determines the sweeping area of CO2 plumes. [Copyright &y& Elsevier]

Abstract: The dynamic mass partitioning and spatial distribution of CO2 trapping mechanisms largely control the long-term isolation performance of geologic storage sites. Although the majority of these physical and chemical sinks have been well characterized individually, much less well defined is our understanding of their relative significance on a mass basis, how this mass partitioning varies as a function of key reservoir properties, and the manner in which partitioning dynamics correlate with isolation performance. In this paper, I first review the resume of trapping mechanisms, outline the fundamental boundary condition and process controls on their spatial distribution and mass partitioning, and describe the distinct distribution and partitioning characteristics of end-member structurally open and closed systems. I then discuss how mass partitioning varies with time, propose a new correlation between partitioning dynamics and isolation performance, and within this framework outline optimal reservoir settings for large-scale CO2 injection. [Copyright &y& Elsevier]

Abstract: We present a sharp-interface mathematical model of CO2 migration in saline aquifers, which accounts for gravity override, capillary trapping, natural groundwater flow, and the shape of the plume during the injection period. The model leads to a nonlinear advection–diffusion equation, where the diffusive term is due to buoyancy forces, not physical diffusion. For the case of interest in geological CO2 storage, in which the mobility ratio is very unfavorable, the mathematical model can be simplified to a hyperbolic equation. We present a complete analytical solution to the hyperbolic model. The main outcome is a closed-form expression that predicts the ultimate footprint on the CO2 plume, and the time scale required for complete trapping. The capillary trapping coefficient emerges as the key parameter in the assessment of CO2 storage in saline aquifers. The expressions derived here have immediate applicability to the risk assessment and capacity estimates of CO2 sequestration at the basin scale. In a companion paper [Szulczewski and Juanes, GHGT-9, Paper 463 (2008)] we apply the model to specific geologic basins. [Copyright &y& Elsevier]

Abstract: The effect of flow instabilities on capillary trapping mechanisms is a major source of uncertainty in CO2 sequestration in deep saline aquifers. Standard macroscopic models of multiphase flow in porous media are unable to explain and quantitatively predict the onset and structure of viscous-unstable flows, such as the displacement of brine by the injected CO2. We present the first step of a research effort aimed at the experimental characterization and mathematical (continuum) modeling of such flows. Existing continuum models of multiphase flow are unable to explain why preferential flow (fingering) occurs during infiltration into homogeneous, dry soil. We present a macroscopic model that reproduces the experimentally observed features of fingered flows. The proposed model is derived using a phase-field methodology and does not introduce new independent parameters. From a linear stability analysis, we predict that finger velocity and finger width both increase with infiltration rate, and the predictions are in quantitative agreement with experiments. [Copyright &y& Elsevier]

Abstract: The super-atomization of liquid CO2 aimed at stable geological storage has been performed. All of geological storage techniques are required to prevent rising up of injected CO2 due to buoyancy effect. As an example, caprock CO2 trapping prevents the CO2 rising up by impermeable layer, however this technique depends onto the geological structure and there are leakage risk. Therefore we proposed a new technique of trapping super-atomized liquid CO2 in the porous structure to realize stable geological storage and to boost the efficiency of storage. In this study, the super-atomization process and the emulsion stability have been observed. As the result, the liquid CO2 was able to be super-atomized the same scale as gap diameter of the sandstone aquifer. [Copyright &y& Elsevier]

Abstract: CO2 can be immobilized in an aquifer as a residual phase trapped by capillary forces. The “inject low and let rise” strategy of storing CO2 in d eep saline aquifers is one method to maximize residual trapping. The more uniform the saturation front during upward movement of CO2, the greater the amount of CO2 trapped in this form. Previous studies suggest that capillary pressure i s a secondary influence on the CO2 plume, and that the permeability field governs the major features of the rising plume. In this work we show that sp atially varying capillary entry pressure can cause qualitatively different plume behavior. To illustrate the behavior, we si mulate buoyancy-driven migration when supercritical CO2 is placed below brine in a heterogeneous domain. After generating geostatistical realizations of permeability, we apply the Leverett -function so that each grid block has a drainage curve ( vs ) physically consistent with its permeability. The behavior of the displacement front depends strongly on the correlation structure of the heterogeneity and upon the magnitude of entry pressure. In a relatively homogeneous domain, capillar ity is a second-order effect. It damps the tendency toward channeling of the rising CO2 front and increases the uniformity of the plume. As the heterogeneity of the aquifer increases, capillarity begins to dominate buoyancy. Regions with smaller permeability, through which single-phase flow would readily occur, can completely block rising CO2, simply because the capillary entry pressure in these regions is somewhat larger than in neighboring regions. These local capillary barriers prevent CO2 from rising and cause it to mov e laterally. The disruption can be so extreme that above-residual saturations of CO2 accumulate below these barriers. These local accumulations can remain undisturbed when the top seal of the aquifer is breached. Thus we distinguish them as a new mode of CO2 trapping, dubbed “local capillary trapping”. Overall, the displacement front is much less uniform in heterog eneous domains. Despite the nonuniformity, the extent of dissolution trapping remains significant, much more than would be expected considering the ramified structure of the displacement front. T he reduction in residual phase trapping is balanced by an increase in local capillary trapping. Thus the extent of immobilization is similar to that found in previous works. [Copyright &y& Elsevier]

Abstract: Safely sequestering CO2 in a deep saline aquifer requires calculating how much CO2 the aquifer can store. Since offsetting nationwide emissions requires sequestering large quantities of CO2, this calculation should apply at the large scale of geologic basins. The only method to calculate storage capacity at the basin scale, however, is not derived from multiphase flow dynamics, which play a critical role in CO2 storage. In this study, we explain a new model to calculate basin-scale storage capacity that is derived from flow dynamics and captures the dynamic phenomena of gravity override and capillary trapping. Despite the fact that the model is dynamic, it is simple since it is a closed form expression with few terms. We demonstrate how to apply it on the Fox Hills Sandstone in the Powder River Basin. [Copyright &y& Elsevier]

Abstract: Motivated by geological carbon dioxide (CO2) storage, we present a simple model for the migration of immiscible gravity currents with constant residual trapping in a two-dimensional confined and sloping aquifer. Residual trapping acts as a loss-term, it reduces the current volume as long as the CO2 plume continues to migrate. Comparison with numerical results shows that the hyperbolic limit of the governing equations is a good approximation for currents with large mobility. In gently sloping aquifers, the current evolution is divided into an initial stage, with power-law decrease of volume, and a later stage, characterized by a rapid decay of the plume volume. Our results suggest that the efficient residual trapping in dipping aquifers may allow CO2 storage in aquifers lacking structural closure, if CO2 is injected far enough from the outcrop of the aquifer. However, the poor vertical sweep may lead to very long migration distances that may limit the storage capacity of in such aquifers. All results presented here are based on [M.A. Hesse, F.M. Orr Jr, H.A. Tchelepi, Gravity currents with residual trapping, J. Fluid Mech. 611 (2008) 35–60.]. [Copyright &y& Elsevier]

Abstract: Numerical simulation using TOUGHREACT software has shown that more than 20Mt of CO2 can be stored for a period up to 10,000 years in a 2-D model system taking from the geology of the Tokyo Bay area. Carbonate precipitation occurs extensively in the front of enlarging plume, forming a shell enclosing CO2. The distribution of dawsonite is predicted to be dependent on the dissolution of plagioclase which presents abundantly in sandstones of the Tokyo Bay area as well as those in young sedimentary strata of Japanese Islands, suggesting its potential importance in the mineral trapping of CO2. [Copyright &y& Elsevier]

Abstract: Numerous research results have been published on the storage science and the technology of CO2 storage in saline aquifers to address the knowledge gaps identified by the IPCC Special Report on Carbon Capture and Storage in 2005. Significant progress has been made towards developing consistent methodologies for the classification and determination of CO2 storage capacity and towards comprehensive guidelines regarding site selection, site characterisation, risk assessment and monitoring and plans. Although advancements have been made with respect to geochemical processes and numerical simulations, a larger portfolio of CO2 storage operations is needed to provide realistic data for model calibration and substantiation of time frames for various trapping mechanisms. The experience from existing storage projects has shown that CO2 geological storage in saline aquifers is a technology that can be successfully and safely applied today. However, proper regulations for CO2 storage are needed to reduce the current uncertainty associated with the economics of CO2 storage and to accelerate the deployment of CCS technology. [Copyright &y& Elsevier]

Abstract: To utilize aquifers without proven seal structures as a CO2 storage reservoir, CO2 should be trapped by residual gas trapping and solubility trapping as well as physical trapping by cap-rock. We investigated the mechanism of the residual gas trapping from a microscopic point of view by means of micro-focused X-ray CT. First, we imaged trapped air bubbles in a Berea sandstone chip after spontaneous imbibition at atmospheric pressure. With the resolution of 6.52 m/pixel, 610 sheets of slice images of 608×608 pixels were reconstructed. Pore structure and trapped bubbles were clearly visualized. Next, distributions of trapped bubbles in Berea and Tako sandstone were imaged in core-flooding at the capillary number of 1.0×10−6. The trapped bubbles consist of two-type; one occupies the center of pore with a pore-scale size and the other has a pore-network scale size. In low porosity porous media such as sandstone, connected bubbles has high contribution to trapped gas saturation. The distributions of trapped bubbles were uniform throughout the core except for the heterogeneity due to sedimentary layers. With a packed bed of glass beads 600 μm in diameter, the effects of capillary number and the injected water volume were investigated. Even in the packed bed of glass beads, which has a high porosity of 38%, once the gas bubbles are trapped, they are stable against the water flow rate that corresponds to the capillary number of 1.0×10−4. Even at very high capillary number of 4.7×10−5, residual gas saturation is independent of volume of injected water up to 15 pore volumes. Third, distributions of the residual gas saturation in the core were measured at supercritical conditions on core scale. The effect of fracture on the residual gas saturation was also investigated. The fracture reduces the maximum CO2 saturation to about 20% at the end of CO2 injection. However, most of the CO2 were trapped after the water injection. The Land type relationship between trapped CO2 saturation and the maximum CO2 saturation was obtained for supercritical CO2. [Copyright &y& Elsevier]

Abstract: We measure the trapped non-wetting phase saturation as a function of the initial saturation in sand packs. The application of the work is for carbon dioxide (CO2) storage in aquifers where capillary trapping is a rapid and effective mechanism to render injected CO2 immobile. We used analogue fluids at ambient conditions. The trapped saturation initially rises linearly with initial saturation to a value of 0.11 for oil/water systems and 0.14 for gas/water systems. There then follows a region where the residual saturation is constant with further increases in initial saturation. [Copyright &y& Elsevier]

Abstract: The end of the Permian period is marked by global warming and the biggest known mass extinction on Earth. The crisis is commonly attributed to the formation of the Siberian Traps Large Igneous Province although the causal mechanisms remain disputed. We show that heating of Tunguska Basin sediments by the ascending magma played a key role in triggering the crisis. Our conclusions are based on extensive field work in Siberia in 2004 and 2006. Heating of organic-rich shale and petroleum bearing evaporites around sill intrusions led to greenhouse gas and halocarbon generation in sufficient volumes to cause global warming and atmospheric ozone depletion. Basin scale gas production potential estimates show that metamorphism of organic matter and petroleum could have generated >100,000 Gt CO2. The gases were released to the end-Permian atmosphere partly through spectacular pipe structures with kilometre-sized craters. Dating of a sill intrusion by the U–Pb method shows that the gas release occurred at 252.0±0.4 million years ago, overlapping in time with the end-Permian global warming and mass extinction. Heating experiments to 275 °C on petroleum-bearing rock salt from Siberia suggests that methyl chloride and methyl bromide were significant components of the erupted gases. The results indicate that global warming and ozone depletion were the two main drivers for the end-Permian environmental crisis. We demonstrate that the composition of the heated sedimentary rocks below the flood basalts is the most important factor in controlling whether a Large Igneous Provinces causes an environmental crisis or not. We propose that a similar mechanism could have been responsible for the Triassic-Jurassic (~200 Ma) global warming and mass extinction, based on the presence of thick sill intrusions in the evaporite deposits of the Amazon Basin in Brazil. [Copyright &y& Elsevier]

Abstract: Sea-level change has been commonly interpreted to be of eustatic origin, and many eustatic events were hypothesized for the Phanerozoic, including several 1–3 Myr long cycles in the Ordovician with magnitudes up to 100 or 200 m. However, sea-level change modeling using stratigraphic data from Northern Estonia, which was an area of slow shallow-marine (< 10 m) deposition through most of the Ordovician, indicates fluctuations of no more than 20 m. In the Late Ordovician the sea level fell only twice for ∼100 m within 1 Myr during the Gondwanian glaciation. Although the sea level remained relatively stable, there were frequent 100–200 m changes of sea depths we inferred with reference to the time spans of stratigraphic units and intervals between tectonic events estimated reliably against stable durations of East Siberian chronozones (biochrons) of the Ordovician. In the absence of eustatic events, the sea-depth changes most likely resulted from rapid crustal uplift and subsidence. According to correlated well-documented Ordovician sections from East Siberia, the rate of crustal subsidence changed rapidly in different periods and in different places of the area, thus being of a regional scale. The controversy between the sea-level stability and the regional-scale variations in sea depths controlled by rates of crustal uplift and subsidence can be resolved assuming a model of variable eclogitization rates in the lower crust caused by lithospheric stress change. Our inferences undermine the traditional petroleum prediction approach implying formation of depositional traps due to rapid eustatic sea-level change. [Copyright &y& Elsevier]

Abstract: Implementation of well completions enabling multiple hydrocarbon reservoirs to be produced by a single well can save production cost and enhance recovery. Aiming at the characteristics of the three types of oil and gas reservoirs in the Jabung block in Indonesia, namely, gas cap oil-rim reservoirs, multiple hydrocarbon reservoirs, and heterogeneous multiple-sand reservoirs, this article puts forward optimized completion methods by using conventional technology and down-hole equipment. The new methods are able to develop multireservoir sands at the same time or successively without additional completion jobs. In addition, the novel completion enables water injection wells to selectively control injection and improve the recovery of hydrocarbons. The above strategies have been applied to different types of reservoirs, providing an effective mean for maximizing hydrocarbon recovery, controlling operating expenditures, and improving the overall benefit of development wells. [Copyright &y& Elsevier]

Abstract: Affected by the South Tianshan orogenesis, the faulted structure patterns in the Wushi Sag are very complex. Aimed to find out the basic characteristics of the structures, this article studies many seismic profile sections, the regional geology, the structural patterns, and the formative stage of the structures. The Wushi Sag has three main fault patterns (face to face thrust, back to back thrust, sphenoid thrust), and many local fault structural patterns (fault-bend fold, fault-propagation fold, duplex structure, outburst structure, growth structure, etc.). There mainly develop four groups of reverse faults (NE, NEE, NW, EW) and one group of NNW trending strike-slip faults. According to the structural background, seismic profiles, and balanced cross sections, the main fault in the studied area experiences at least five evolving stages, which are, pre-Mesozoic, late Permian – early Tertiary, Jurassic, late Jurassic – early Cretaceous, and late Neogene. The structural styles have a close relationship with source rocks, hydrocarbon reservoirs, and the character and distribution of petroleum systems. [Copyright &y& Elsevier]

The history matching (HM) hydrocarbon reservoir inverse problem is ill-posed because its solution may be non-unique or unstable. Variability of acceptable solutions around local minima may be very large. Nonetheless, it is a common practice in HM to find a unique reservoir model, although there is no guarantee that this model represents the geology. Qualitative geological information is generally not considered because of difficulties to express them mathematically. Here, we incorporate 'smoothness' in the spatial variation of physical properties as an example of a geological qualitative constraint that can be mathematically incorporated in an objective function also honouring the data. The constraint is valid if lateral continuity exists (e.g. fluvial-deltaic siliciclastic reservoirs). We mean smoothness by conditioning the permeability and/or porosity difference between adjacent grid blocks to be small. We use a synthetic 2D water-oil model and a solution search technique allowing characterising both the optimum solution and its variability. The smoothness constraint reduces the variance of the estimates by introducing bias in the solutions still preserving good match. The key point to achieve an optimum trade-off between stability and data match is the tuning of the parameter, controlling the relative importance of the constraint in the objective function. The smoothness constraint cannot be applied to all reservoirs. However, we corroborate the idea that a 'tool box' of HM can be designed; each 'tool' can incorporate a different constraint. Therefore, the interpreter can judiciously choose a specific tool from this tool box according to the adherence of its constraint to the particular reservoir being studied. [ABSTRACT FROM AUTHOR]

The trap efficiency of a catcher in wind erosion measurements plays a significant role, and in many cases suspension trap efficiencies at high wind velocities are still unknown. The sediment trap efficiency generally changes with particles size and with wind speed. In this study, the efficiency of Vaseline Slide (VS) and Modified Wilson and Cooke (MWAC) catchers were determined with different sand particle sizes (<50, <75, 50–75, 200–400, and 400–500 μm) at a fixed wind speed (13.3 ms−1) and with different soil textures at different wind velocities (10.3, 12.3, and 14.3 ms−1) in the wind tunnel of the International Center for Eremology (ICE), Ghent University, Belgium. The traps were placed at different heights (4, 6.5, 13, 20, 120, and 192 cm for VS and 1.5, 3, 5, 8, 11, and 30 cm for MWAC) to catch saltating and suspended sediments in a 12-m long, 1.2-m wide and 3.2-m high working section of the wind tunnel. In the sand particle experiments, the efficiency of the VS catcher was 92% for particles smaller than 50 μm and decreased with increasing particles size, falling to 2.2% for 400–500 μm particle size at 13.4 ms−1. However, the MWAC’s efficiency was 0% for particles smaller than 50 μm and increased with increasing particle size to 69.5% at 400–500 μm. In the experiments with different soil textures, the efficiency of each catcher significantly changed with soil and with wind speed. It also considerably varied with the catchers: for instance, for sand (S), the MWAC efficiency was very high (67.4, 113.4, and 90.5% at 10.3, 12.3, and 14.4 ms−1, respectively) while the efficiency of VS was relatively very low (5.2, 4.4, and 1.9% at 10.3, 12.3, and 14.4 ms−1, respectively). Results indicated that the efficiency depends critically on the particle size, type of catcher, and wind speed, and these could be helpful to increase the robustness of wind erosion measurements. [ABSTRACT FROM AUTHOR]

Abstract: The fold-and-thrust belt in the northwestern margin of the Junggar Basin is composed of the northern monocline belt, the middle syncline belt, the Ke-Wu thrust belt, and the frontal slope belt, and is divided into the upper and lower structural layers in vertical. The upper structural layer precedes the lower one in terms of thrust sequence. Inferred from the restoration of unconformities, the motion of thrust faults started in late Triassic, activated in succession in Jurassic, and stopped in Cretaceous. The footwall venture exploration should aim at “cap brim” traps, especially in the triangular region, where the Dazhuluogou tear fault and Ke-Wu thrust belt intersect and the exploration horizon imbeds moderately, and then aim at the deep anticline traps in duplex structures when obtaining the essential data of deep geology and the velocity data. [Copyright &y& Elsevier]

The article analyzes the results of the exploratory effort in the South-Caspian Basin and the causes of failures to discover substantial hydrocarbon reserves in 1995 through 2005. A geologic concept is proposed that may help improve exploratory drilling efficiency. The region's reserves and resources are evaluated. [ABSTRACT FROM AUTHOR]

Controlled-source electromagnetic (CSEM) field surveys offer a geophysical method to discriminate between high and low hydrocarbon saturations in a potential reservoir. However, the same geological processes that create the possible hydrocarbon reservoir may also create topography and near-surface variations of resistivity (e.g., shallow gas or hydrates) that can complicate the interpretation of CSEM data. In this paper, we discuss the interpretation of such data over a thrust belt prospect in deepwater Sabah, Malaysia. We show that detailed modeling of the key scenarios can help us understand the contributions of topography, near-surface hydrates, and possible hydrocarbons at reservoir depth. Complexity at the surface and at depth requires a 3D electromagnetic modeling code that can handle realistic ten-million-cell models. This has been achieved by using an iterative solver based on a multigrid preconditioner, finite-difference approach with frequency-dependent grid adaptation. [ABSTRACT FROM AUTHOR]

The change in reservoir pore pressure due to the production of hydrocarbons leads to anisotropic changes in the stress field acting on the reservoir. Reservoir stress path is defined as the ratio of the change in effective horizontal stress to the change in effective vertical stress from the initial reservoir conditions, and strongly influences the depletion-induced compaction behaviour of the reservoir. Seismic velocities in sandstones vary with stress due to the presence of stress-sensitive regions within the rock, such as grain boundaries, microcracks, fractures, etc. Since the response of any microcracks and grain boundaries to a change in stress depends on their orientation relative to the principal stress axes, elastic-wave velocities are sensitive to reservoir stress path. The vertical P- and S-wave velocities, the small-offset P- and SV-wave normal-moveout (NMO) velocities, and the P-wave amplitude-versus-offset (AVO) are sensitive to different combinations of vertical and horizontal stress. The relationships between these quantities and the change in stress can be calibrated using a repeat seismic, sonic log, checkshot or vertical seismic profile (VSP) at the location of a well at which the change in reservoir pressure has been measured. Alternatively, the variation of velocity with azimuth and distance from the borehole, obtained by dipole radial profiling, can be used. Having calibrated these relationships, the theory allows the reservoir stress path to be monitored using time-lapse seismic by combining changes in the vertical P-wave impedance, changes in the P-wave NMO and AVO behaviour, and changes in the S-wave impedance. [ABSTRACT FROM AUTHOR]

The area comprising the NE Nile Delta and adjacent northern Sinai is an important hydrocarbon province in Egypt, but the origin of the hydrocarbons and their migration is not fully understood. In this paper, we evaluate organic source facies and assess the results of basin modelling in order to improve our understanding of the regional petroleum system. Organic-geochemical and petrographic analyses of 800 rock samples ranging in age from Early Jurassic to Pleistocene were used in this study. Most of the samples studied had moderate to high TOC contents, and kerogen was a mixture of Types II and III with a wide range of petroleum generation potentials from very poor to very good. Thermal and burial history models indicate that the source rocks entered the early-mature/mature stage in very recent times (Pleistocene to Recent). The top of the oil window ranges in depth from 1,800 m to 4,500 m, whereas the bottom of the oil window was not reached by most of the studied wells. In combination with numerical modelling results, structure contour maps for key horizons reveal possible migration trends and prospective areas. We tentatively identify prospective targets for hydrocarbon exploration, both in the Tertiary sequence and in the Cretaceous succession, especially where carbonate build-ups are present. [ABSTRACT FROM AUTHOR]

We propose a decision-making approach for optimizing the profitability of hydrocarbon reservoirs. The proposed approach addresses the overwhelming complexity of the overall optimization problem by suggesting an oilfield operations hierarchy that entails different time scales. We discuss system identification, optimization, and control that are appropriate at various levels of the hierarchy and capitalize on the abilities of permanently instrumented and remotely actuated fields. Optimization is performed in real-time and is based on feedback. We provide details on real-time identification of hybrid models and their use at the scheduling and supervisory control levels. Case studies using field-calibrated simulation data demonstrate the applicability and value of the proposed approach. Directions for future development are given. [ABSTRACT FROM AUTHOR]

Most commercial oil sands exhibit shale resistivity ratios (ratio of normal R shn to observed R sho ) of less than approximately 1.6 in adjacent shales and can be reached without an expensive string of protection pipe. On the other hand, some experts claim that “no commercial production is found when the shale resistivity ratio reaches and/or exceeds 3.5.” This statement, however, needs further investigation Such wells often are highly productive initially and are characterized by extremely fast pressure depletion. Based on extensive compaction studies of rocks, the authors argue that the latter is due to plastic deformation (irreversible compaction) in undercompacted overpressured rocks with increasing effective stress soon after production is initiated (or during well testing). Thus, well tests could be quite misleading, and many er roneously condemned overpressured reservoirs should be reexamined, reevaluated, and strategies be developed to recover the oil and gas from these stress-sensitive reservoirs. [ABSTRACT FROM AUTHOR]

The recognition of traps most likely to contain hydrocarbons, while making reconnaissance surveys or at an early stage of exploration, has never been an easy task. Utilizing mathematical indicators can allow the identification of likely traps containing oil and/or gas accumulation during early exploratory drilling programs. The guidelines set forth in this article permit one to refine the exploration and delineation operations and focus exploration efforts on only those traps that are most likely to contain economic hydrocarbons. This “focusing” saves valuable time and economic resources. [ABSTRACT FROM AUTHOR]

The thermal diusion phenomena, also known as the Soret eect, is important for the study of compositional variation in hydrocarbon reservoirs. Several theoretical models have been developed over the years to predict the thermodiusion coefficient of an organic mixture. Firoozabadi et al. [1] developed an analytical relationship between the thermal, molecular, and pressure diusion coefficients based on the approach of Dougherty and Drickamer [2]. The distinctive feature of Firoozabadi's model is its ability to be used not only for binary mixtures but also for multicomponent mixtures. The verification of Firoozabadi's model by numerical simulations was limited to binary mixtures only because of a lack of experimental data on thermodiusion coefficients in multicomponent hydrocarbon mixtures. However, Platten et al. [3] were able to measure the thermodiusion coefficients of a ternary hydrocarbon mixture experimentally by utilizing the thermogravitational column technique, hence making it possible to verify the theoretical model. This paper will compare the density, thermodiusion, and molecular diusion coefficients obtained with the Fontainebleau benchmark values for binary mixtures of n-dodecane, isobutylbenzene, and tetrahydronaphtalene. The accuracy of the numerical results from the Firoozabadi's model for ternary hydrocarbon mixtures is investigated. Results reveal a positive agreement between experimental and numerical data. [ABSTRACT FROM AUTHOR]

Abstract: This article introduces a methodology for integrating geochemical data in reservoir simulations to improve hydrocarbon reservoir models. The method exploits routine measurements of naturally existing inorganic ion concentration in hydrocarbon reservoir production wells, and uses the ions as non-partitioning water tracers. The methodology is demonstrated on a North Sea field case, using the field''s reservoir model, together with geochemical information (SO4 2−, Mg2+, K+, Ba2+, Sr2+, Ca2+ and Cl− concentrations) from the field''s producers. Based on the dataset, some of the ions are shown to behave almost as ideal seawater tracers, i.e. without sorption to the matrix, ion exchange with the matrix or scale formation with other ions in the formation water. Moreover, the dataset shows that ion concentrations in pure formation water vary according to formation. This information can be used to allocate produced water to specific water-producing zones in commingled production. Based on an evaluation of the available data, one inorganic component, SO4 2−, is used as a natural seawater tracer. Introducing SO4 2− as a natural tracer in a tracer simulation has revealed a potential for improvements of the reservoir model. By tracking the injected seawater it was possible to identify underestimated fault lengths in the reservoir model. The demonstration confirms that geochemical data are valuable additional information for reservoir characterization, and shows that integration of geochemical data into reservoir simulation procedures can improve reservoir simulation models. [Copyright &y& Elsevier]

This paper describes the measurements of the acoustic and petrophysical properties of two suites of low-shale sandstone samples from North Sea hydrocarbon reservoirs, under simulated reservoir conditions. The acoustic velocities and quality factors of the samples, saturated with different pore fluids (brine, dead oil and kerosene), were measured at a frequency of about 0.8 MHz and over a range of pressures from 5 MPa to 40 MPa. The compressional-wave velocity is strongly correlated with the shear-wave velocity in this suite of rocks. The ratio VP/ VS varies significantly with change of both pore-fluid type and differential pressure, confirming the usefulness of this parameter for seismic monitoring of producing reservoirs. The results of quality factor measurements were compared with predictions from Biot-flow and squirt-flow loss mechanisms. The results suggested that the dominating loss in these samples is due to squirt-flow of fluid between the pores of various geometries. The contribution of the Biot-flow loss mechanism to the total loss is negligible. The compressional-wave quality factor was shown to be inversely correlated with rock permeability, suggesting the possibility of using attenuation as a permeability indicator tool in low-shale, high-porosity sandstone reservoirs. [ABSTRACT FROM AUTHOR]

This paper proposes a method for quantitative integration of seismic (elastic) anisotropy attributes with reservoir-performance data as an aid in characterizing systems of natural fractures in hydrocarbon reservoirs. This method is demonstrated through application to history matching of reservoir performance using synthetic test cases. Discrete-feature-network (DFN) modeling is a powerful tool for developing fieldwide stochastic realizations of fracture networks in petroleum reservoirs. Such models are typically well conditioned in the vicinity of the wellbore through incorporation of core data, borehole imagery, and pressure-transient data. Model uncertainty generally increases with distance from the borehole. Three-dimensional seismic data provide uncalibrated information throughout the interwell space. Some elementary seismic attributes such as horizon curvature and impedance anomalies have been used to guide estimates of fracture trend and intensity (fracture area per unit volume) in DFN modeling through geostatistical calibration with borehole and other data. However, these attributes often provide only weak statistical correlation with fracture-system characteristics. The presence of a system of natural fractures in a reservoir induces elastic anisotropy that can be observed in seismic data. Elastic attributes such as azimuthally dependent normal moveout velocity (ANMO), reflection amplitude vs. azimuth (AVAZ), and shear-wave birefringence can be inverted from 3D-seismic data. Anisotropic elastic theory provides physical relationships among these attributes and fracture-system properties such as trend and intensity. Effective-elastic-media models allow forward modeling of elastic properties for fractured media. A technique has been developed in which both reservoir-performance data and seismic anisotropic attributes are used in an objective function for gradient-based optimization of selected fracture-system parameters. The proposed integration method... [ABSTRACT FROM AUTHOR]

Abstract We study counter-current imbibition, where a strongly wetting phase (water) displaces non-wetting phase spontaneously under the influence of capillary forces such that the non-wetting phase moves in the opposite direction to the water. We use an approximate analytical approach to derive an expression for saturation profile when the viscosity of the non-wetting phase is non-negligible. This makes the approach applicable to water flooding in hydrocarbon reservoirs, or the displacement of non-aqueous phase liquid (NAPL) by water. We find the recovery of non-wetting phase as a function of time for one-dimensional flow. We compare our predictions with experimental results in the literature. Our formulation reproduces experimental data accurately and is superior to previously proposed empirical models. [ABSTRACT FROM AUTHOR]

The Siberian traps rank among the largest flood basalt provinces in the world. Major magmatic activity is restricted to several short periods of less than 1 Myr around the Permo-Triassic boundary. We measured the anisotropy of magnetic susceptibility (AMS) of 183 basaltic samples from 28 individual lava flows belonging to the northwestern part of the flood basalt province, in order to test the reliability of such data in structural interpretation. These preliminary AMS data show a remarkably consistent pattern of magnetic lineations, that likely reflect the primary flow-related texture of the basalt. Our results also emphasize that AMS data are consistent with the well-documented petrological and geochronological data. The inferred flow directions are also consistent with flow directions expected from isopach maps. Our results suggest that the entire 2 km-thick lava pile was fed by fissure eruptions located in the rifted basin that bound the Siberian platform, and was controlled by topographical features, particularly major rift zones. [ABSTRACT FROM AUTHOR]

An automatic monitoring system has been developed to process continuously recorded microseismic data and locate the associated events. To this end we use P- and S-wave travel times and the direction of the incoming wave field. The processing is organised in four modules: (i) a multi-channel detection algorithm based on signal-to-noise ratios, (ii) a P-wave onset determination based on error prediction filtering with an auto-regressive model, (iii) a P-wave polarisation analysis providing the direction of the incoming wave field, and (iv) a rotation of seismic traces into the ray coordinate system with subsequent S-wave onset determination. For a homogeneous velocity model the event hypocenter is determined by a linearised inversion technique, and for a three-dimensional (3D) velocity model a directed grid search method or the neighbourhood algorithm is applied. We applied the monitoring system to a microseismic data set from the Ekofisk oil field in the North Sea and located about 2000 microseismic events close to the borehole receiver string. Most of the microseismic events occurred in clusters and in a depth range from 2800 to about 3050 m depth. Location errors were estimated by bootstrapping, and a comparison between results from directed grid search and neighbourhood algorithm revealed a high level of consistency. [Copyright &y& Elsevier]

Reports that the Kela-2 gas field is located in the center of Kelasu structural belt in Kuqa Depression. Fact that this trap is one of a series of traps in the folded belts which are distributed in a string of pearls in the dual structure; Statement that the primary gasbearing layers are sandstone of Lower Cretaceous K&sub1;bs while the secondary layers are dolomite member and glutenite member of Lower Tertiary E&sub1-2;km and sandstone of Lower Cretaceous K&sub1;b; Reference to the fact that the main component of natural gas is methane whose content is higher than 97%; Characterization by dry gas whose source rock is Jurassic coal measure; Formation of the Kela-2 structural trap during the Xiyu period, becoming a reservoir in the late time; Formation of late and the thick seal rock of Lower Tertiary gipsmantle in the reservoir as the avail reason why the giant Kela-2 gas field has been well kept; Conclusion that the abnormal high pressure of the Kela-2 gas field results from the strong structural compression in the northern part during the Xiyu period.

Reports that the Kuqa depression bears not only plenty of natural gas, but also a large amount of condensate and small quantity of crude oil. Confirmation in this paper that, based on the geochemical correlation between the Jurassic and Triassic terrestrial hydrocarbon source rock, the natural gas in Kuqa depression belongs to coal-type gas and the main gas source rock is attributed to the middle to lower Jurassic coal series formation, while the main oil source rock is the upper Triassic lacustrine mudstone; Indication by the authors that Kuqa depression was slowly subsided in Mesozoic, but rapidly went down in Late Tertiary, which made the Jurassic and Triassic source rock suddenly deep-buried and rapidly evolved to high and over-mature phase since 5 Ma; Statement that the Triassic source rock is postponed to the Early Miocene during 23-12 Ma when entering the oil-generating peak, while the Jurassic is suspended to the latest 5 Ma, especially since 2.5 Ma to the dry gas-generating period, which is one of the characteristics of the source rock thermal evolution in Kuqa depression; Presentation in this paper of a two-stage trapping and late gas trapping model in Kuqa depression whose characteristics are: The main oil and gas reservoirs have different sources; Formation of the oil reservoir is early while the gas reservoir is formed lately; Reference to the fact that, during the early stage, it, mainly as oil, takes long distance lateral migration, while in the later stage, it, mainly as gas, takes the vertical migration and also has lateral migration; Formation of the trap formed in different time on the south and north sides of the depression and evolution into a distributional pattern with oil in the south part and gas in the north, also oil on the outer ring and gas on the inner ring; Reference in this paper to the fact that late trapping of the natural gas in Kuqa depression is favorable for the preservation of large gas fields.

Studies the controlling factors of coal-formed great-medium gas fields in China. Definition of coal-formed gas; Coal-formed gas generating center and its surrounding area; Low gas potential areas; Large-medium traps with late pool-forming period; Traps related to the paleo-uplifts in coal-formed gas generating area; Effective fracture trap related to coal measures.

Presents a study to evaluate the geological uncertainty and economic analysis in a rapid simulation of hydrocarbon exploration. How the offshore Nova Scotia Shelf Basin was selected for demonstrating the methodology; Consideration of the approximation method by Manly which has been applied to hydrocarbon discovery process modeling; Approximation of the expected value and the standard deviation of the total discovery volume for a given exploratory effort.

Clastic reservoirs saturated with heavy oils have been observed to exhibit a marked relationship between velocity of propagation of acoustic waves and changes introduced by certain kinds of enhanced oil recovery procedures, including heating of the reservoir. This observation forms the basis for a method of monitoring the changes which occur in the reservoir when these enhanced oil recovery (EOR) procedures are used. New developments in diffraction tomographic imaging allow accurate, high-resolution images to be obtained in hydrocarbon reservoirs, clearly delineating the zones affected by these enhanced oil recovery procedures. When both compressional and shear wave data can be obtained, additional physical parameters such as Poissons ratio can be reconstructed. [ABSTRACT FROM AUTHOR]