Schlumberger (British Virgin Islands)

Abstract A class of algorithms is introduced for the rapid numerical application of a class of linear operators to arbitrary vectors. Previously published schemes of this type utilize detailed analytical information about the operators being applied and are specific to extremely narrow classes of matrices. In contrast, the methods presented here are based on the recently developed theory of wavelets and are applicable to all Calderon‐Zygmund and pseudo‐differential operators. The algorithms of this paper require order O ( N ) or O ( N log N ) operations to apply an N × N matrix to a vector (depending on the particular operator and the version of the algorithm being used), and our numerical experiments indicate that many previously intractable problems become manageable with the techniques presented here.

KL-ONE is o system for representing knowledge in Artificial Intelligence programs. It has been developed and refined over o long period ond hos been used in both basic research and implemented knowledge-based systems in a number of places in the Al community. Here we present the kernel ideas of KL-ONE, emphasizing its ability to form complex structured descriptions. In addition to detailing oil of KL-ONE’s description-forming structures, we discuss o bit of the philosophy underlying the system, highlight notions of taxonomy and clossificotion that ore central to it, ond include on extended example of the use of KL-ONE and its classifier in a recognition task.

Abstract We develop a theory for dielectric response of water-saturated rocks based on a realistic model of the pore space. The absence of a percolation threshold manifest in Archie’s law, porecasts, electron-micrographs, and general theories of formation of detrital sedimentary rocks indicates that the pore spaces within such rocks remain interconnected to very low values of the porosity ϕ. In the simplest geometric model for which the conducting paths remain interconnected, each grain is envisioned to be coated with water. The dielectric constant of the assembly of water-coated grains is obtained by a self-consistent effective medium theory. In the dc limit, this gives Maxwell's relation for conductivity σ of the rock σ = 2σωφ/(3 − φ), where σω is the conductivity of water. In order to include the local environmental effects around a grain, a self-similar model is generated by envisioning that each rock grain itself is coated with a skin made of other coated spheres; the coating at each level consists of other coated spheres. The self-consistent complex dielectric constant ɛ* is given in this model in terms of that of water ɛω* and of rock ɛm*, by [(ɛm*−ɛ*)/(ɛm*−ɛω*)][ɛω*/ɛ*]1/3=φ for spherical particles. This gives, in the dc limit, σ = σωφ3/2. For nonspherical particles, the exponent m in Archie's law σ = σωφm is greater than 3/2 for the plate-like grains or cylinders with axis perpendicular to the external field and smaller than 3/2 for plates or cylindrical particles with axis parallel to the external field. Artificial rocks with a wide range of porosities were made from glass beads. We present data on the glass bead rocks for dc conductivity and the dielectric constant at 1.1 GHz. The data follow the conductivity and the dielectric responses given by the self-similar model. The present theory fails to explain the salinity dependence of ɛ* at lower frequencies.

KL‐ONE is a system for representing knowledge in Artificial Intelligence programs. It has been developed and refined over a long period and has been used in both basic research and implemented knowledge‐based systems in a number of places in the AI community. Here we present the kernel ideas of KL‐ONE, emphasizing its ability to form complex structured descriptions. In addition to detailing all of KL‐ONE's description‐forming structures, we discuss a bit of the philosophy underlying the system, highlight notions of taxonomy and classification that are central to it, and include an extended example of the use of KL‐ONE and its classifier in a recognition task.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMolecular monolayers and films. A panel report for the Materials Sciences Division of the Department of EnergyJerome D. Swalen, D. L. Allara, J. D. Andrade, E. A. Chandross, S. Garoff, J. Israelachvili, T. J. McCarthy, R. Murray, R. F. Pease, and Cite this: Langmuir 1987, 3, 6, 932–950Publication Date (Print):November 1, 1987Publication History Published online1 May 2002Published inissue 1 November 1987https://pubs.acs.org/doi/10.1021/la00078a011https://doi.org/10.1021/la00078a011research-articleACS PublicationsRequest reuse permissionsArticle Views1891Altmetric-Citations748LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Summary A well-test interpretation method based on the analysis of the time rate of pressure change and the actual pressure response is discussed. A differentiation algorithm is proposed, and several field examples illustrate how the method simplifies the analysis process, making interpretation of well tests easier and more accurate.

Abstract Shales are complex porous materials, normally consisting of percolating and interpenetrating fluid and solid phases. The solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure. The shape, orientation, and connection of the two phases control the anisotropic elastic properties of the composite solid. We develop a theoretical framework that allows us to predict the effective elastic properties of shales. Its usefulness is demonstrated with numerical modeling and by comparison with established ultrasonic laboratory experiments. The theory is based on a combination of anisotropic formulations of the self-consistent (SCA) and differential effective-medium (DEM) ap proximations. This combination guarantees that both the fluid and solid phases percolate at all porosities. Our modeling of the elastic properties of shales proceeds in four steps. First, we consider the case of an aligned biconnected clay-fluid composite composed of ellipsoidal inclusions. Anisotropic elastic constants are estimated for a clay-fluid composite as a function of the fluid-filled porosity and the aspect ratio of the inclusions. Second, a new processing technique is developed to estimate the distribution of clay platelet orientations from digitized scanning electron microphotographs (SEM). Third, the derived clay platelet distribution is employed to estimate the effective elastic parameters of a solid comprising clay-fluid composites oriented at different angles. Finally, silt minerals are included in the calculations as isolated spherical inclusions.

Abstract Hydraulic fracturing in shale gas reservoirs has often resulted in complex fracture network growth, as evidenced by microseismic monitoring. The nature and degree of fracture complexity must be clearly understood to optimize stimulation design and completion strategy. Unfortunately, the existing single planar fracture models used in the industry today are not able to simulate complex fracture networks. A new hydraulic fracture model is developed to simulate complex fracture network propagation in a formation with preexisting natural fractures. The model solves a system of equations governing fracture deformation, height growth, fluid flow, and proppant transport in a complex fracture network with multiple propagating fracture tips. The interaction between a hydraulic fracture and pre-existing natural fractures is taken into account by using an analytical crossing model and is validated against experimental data. The model is able to predict whether a hydraulic fracture front crosses or is arrested by a natural fracture it encounters, which leads to complexity. It also considers the mechanical interaction among the adjacent fractures (i.e., the "stress shadow" effect). An efficient numerical scheme is used in the model so it can simulate the complex problem in a relatively short computation time to allow for day-to-day engineering design use. Simulation results from the new complex fracture model show that stress anisotropy, natural fractures, and interfacial friction play critical roles in creating fracture network complexity. Decreasing stress anisotropy or interfacial friction can change the induced fracture geometry from a bi-wing fracture to a complex fracture network for the same initial natural fractures. The results presented illustrate the importance of rock fabrics and stresses on fracture complexity in unconventional reservoirs. They have major implications on matching microseismic observations and improving fracture stimulation design.

Abstract The simplest effective model of a formation containing a single fracture system is transversely isotropic with a horizontal symmetry axis (HTI). Reflection seismic signatures in HTI media, such as NMO velocity and amplitude variation with offset (AVO) gradient, can be conveniently described by the Thomsen-type anisotropic parameters ∊(V), δ(V), and γ(V). Here, we use the linear slip theory of Schoenberg and co-workers and the models developed by Hudson and Thomsen for penny-shaped cracks to relate the anisotropic parameters to the physical properties of the fracture network and to devise fracture characterization procedures based on surface seismic measurements. Concise expressions for ∊(V), δ(V), and γ(V), linearized in the crack density, show a substantial difference between the values of the anisotropic parameters for isolated fluid-filled and dry (gas-filled) penny-shaped cracks. While the dry-crack model is close to elliptical with ∊(V) ≈ δ(V), for thin fluid-filled cracks ∊(V) ≈ 0 and the absolute value of δ(V) for typical VS/VP ratios in the background is close to the crack density. The parameters ∊(V) and δ(V) for models with partial saturation or hydraulically connected cracks and pores always lie between the values for dry and isolated fluid-filled cracks. We also demonstrate that all possible pairs of ∊(V) and δ(V) occupy a relatively narrow triangular area in the [∊(V), δ(V)]-plane, which can be used to identify the fracture-induced HTI model from seismic data. The parameter δ(V), along with the fracture orientation, can be obtained from the P-wave NMO ellipse for a horizontal reflector. Given δ(V), the NMO velocity of a dipping event or nonhyperbolic moveout can be inverted for ∊(V). The remaining anisotropic coefficient, γ(V), can be determined from the constraint on the parameters of vertically fractured HTI media if an estimate of the VS/VP ratio is available. Alternatively, it is possible to find γ(V) by combining the NMO ellipse for horizontal events with the azimuthal variation of the P-wave AVO gradient. Also, we present a concise approximation for the AVO gradient of converted (PS) modes and show that all three relevant anisotropic coefficients of HTI media can be determined by the joint inversion of the AVO gradients or NMO velocities of P- and PS-waves. For purposes of evaluating the properties of the fractures, it is convenient to recalculate the anisotropic coefficients into the normal (ΔN) and tangential (ΔT) weaknesses of the fracture system. If the HTI model results from penny-shaped cracks, ΔT gives a direct estimate of the crack density and the ratio ΔN/ΔT is a sensitive indicator of fluid saturation. However, while there is a substantial difference between the values of ΔN/ΔT for isolated fluid-filled cracks and dry cracks, interpretation of intermediate values of ΔN/ΔT for porous rocks requires accounting for the hydraulic interaction between cracks and pores.

Abstract A simple petrophysical model proposed by Waxman and Smits (WS)1 in 1968 and Waxman and Thomas (WT)2 in 1972 accounts for the results of an extensive experimental study on the effects of clays on the resistivity of shaly sands. This model has been well accepted by the industry despite a few inconsistencies with experimental results. It is proposed that these inconsistencies resulted from the unaccounted presence of salt-free water at the clay/water interface. Electrochemistry indicates that this water should exist, but is there enough to influence the results? Both a theoretical study and reinterpretation of Waxman-Smits-Thomas data show that there is. The corresponding new model starts from the Waxman and Smits concept of supplementing the water conductivity with a conductivity from the clay counterions. The crucial step, however, is equating each of these conductivity terms to a particular type of water, each occupying a representative volume of the total porosity. This approach has been named the "dual-water" (DW) model because of these two water types—the conductivity and volume fraction of each being predicted by the model. The DW model has been tested on most of the core data reported in Refs. 1 and 2. The DW concept is also supported by log data3 and has been successfully applied to the interpretation of thousands of wells. However, the scope of this paper remains limited to the theoretical and experimental bases of the DW model.

ABSTRACT A model of parallel slip interfaces simulates the behaviour of a fracture system composed of large, closely spaced, aligned joints. The model admits any fracture system anisotropy: triclinic (the most general), monoclinic, orthorhombic or transversely isotropic, and this is specified by the form of the 3 × 3 fracture system compliance matrix. The fracture system may be embedded in an anisotropic elastic background with no restrictions on the type of anisotropy. To compute the long wavelength equivalent moduli of the fractured medium requires at most the inversion of two 3 × 3 matrices. When the fractures are assumed on average to have rotational symmetry (transversely isotropic fracture system behaviour) and the background is assumed isotropic, the resulting equivalent medium is transversely isotropic and the effect of the additional compliance of the fracture system may be specified by two parameters (in addition to the two isotropic parameters of the isotropic background). Dilute systems of flat aligned microcracks in an isotropic background yield an equivalent medium of the same form as that of the isotropic medium with large joints, i.e. there are two additional parameters due to the presence of the microcracks which play roles in the stress‐strain relations of the equivalent medium identical to those played by the parameters due to the presence of large joints. Thus, knowledge of the total of four parameters describing the anisotropy of such a fractured medium tells nothing of the size or concentration of the aligned fractures but does contain information as to the overall excess compliance due to the fracture system and its orientation. As the aligned microcracks, which were assumed to be ellipsoidal, with very small aspect ratio are allowed to become non‐fiat, i.e. have a growing aspect ratio, the moduli of the equivalent medium begin to diverge from the standard form of the moduli for flat cracks. The divergence is faster for higher crack densities but only becomes significant for microcracks of aspect ratios approaching 0.3.

Summary Borehole measurements of the nuclear magnetic resonance (NMR) properties of rocks have been of interest for many years, especially for estimating permeability. This paper presents laboratory measurements of the NMR properties of water-saturated rocks and shows that permeability can be estimated well with expressions of the form ϕ4T12, where T1 is the relaxation time constant of the longitudinal nuclear magnetization of hydrogen nuclei. Different methods of representing the laboratory-measured T1 curves are shown, including a new one called the stretched-exponential representation. An improved method for estimating T1 parameters from borehole measurements that can be used with either old or new representations is presented.

Abstract Seismic wave attenuation in rocks was studied experimentally, with particular attention focused on frictional sliding and fluid flow mechanisms. Sandstone bars were resonated at frequencies from 500 to 9000 Hz, and the effects of confining pressure, pore pressure, degree of saturation, strain amplitude, and frequency were studied. Observed changes in attenuation and velocity with strain amplitude are interpreted as evidence for frictional sliding at grain contacts. Since this amplitude dependence disappears at strains and confining pressures typical of seismic wave propagation in the earth, we infer that frictional sliding is not a significant source of seismic attenuation in situ. Partial water saturation significantly increases the attenuation of both compressional (P) and shear (S) waves relative to that in dry rock, resulting in greater P-wave than S-wave attenuation. Complete saturation maximizes S-wave attenuation but causes a reduction in P-wave attenuation. These effects can be interpreted in terms of wave induced pore fluid flow. The ratio of compressional to shear attenuation is found to be a more sensitive and reliable indicator of partial gas saturation than is the corresponding velocity ratio. Potential applications may exist in exploration for natural gas and geothermal steam reservoirs.

This article examines the evolution of policy recommendations concerning rural land issues since the formulation of the World Bank's “Land Reform Policy Paper” in 1975. That paper set out three guiding principles: the desirability of owner-operated family farms; the need for markets to permit land to be transferred to more productive users; and the importance of an egalitarian asset distribution. In the 25 years since that paper was published, these guiding principles have remained the same, but it is now recognized that communal tenure systems can be more cost-effective than formal title, that titling programs should be judged on their equity as well as their efficiency, that the potential of land rental markets has often been severely underestimated, that land-sale markets enhance efficiency only if they are integrated into a broader effort at developing rural factor markets, and that land reform is more likely to result in a reduction of poverty if it harnesses (rather than undermines) the operation of land markets and is implemented in a decentralized fashion. Achieving land policies that incorporate these elements requires a coherent legal and institutional framework together with greater reliance on pilot programs to examine the applicability of interventions under local conditions.

Abstract Imaging of microseismic data is the process by which we use information about the source locations, timing, and mechanisms of the induced seismic events to make inferences about the structure of a petroleum reservoir or the changes that accompany injections into or production from the reservoir. A few key projects were instrumental in the development of downhole microseismic imaging. Most recent microseismic projects involve imaging hydraulic-fracture stimulations, which has grown into a widespread fracture diagnostic technology. This growth in the application of the technology is attributed to the success of imaging the fracture complexity of the Barnett Shale in the Fort Worth basin, Texas, and the commercial value of the information obtained to improvecompletions and ultimately production in the field. The use of commercial imaging in the Barnett is traced back to earlier investigations to prove the technology with the Cotton Valley imaging project and earlier experiments at the M-Site in the Piceance basin, Colorado. Perhaps the earliest example of microseismic imaging using data from downhole recording was a hydraulic fracture monitored in 1974, also in the Piceance basin. However, early work is also documented where investigators focused on identifying microseismic trace characteristics without attempting to locate the microseismic sources. Applications of microseismic reservoir monitoring can be tracked from current steam-injection imaging, deformation associated with reservoir compaction in the Yibal field in Oman and the Ekofisk and Valhall fields in the North Sea, and production-induced activity in Kentucky, U.S.A.

Abstract Unconventional reservoirs such as gas shales and tight gas sands require technology-based solutions for optimum development. The successful exploitation of these reservoirs has relied on some combination of horizontal drilling, multi-stage completions, innovative fracturing and fracture mapping to engineer economic completions. However, the requirements for economic production all hinge on the matrix permeability of these reservoirs, supplemented by the conductivity that can be generated in hydraulic fractures and network fracture systems. Simulations demonstrate that ultra-low shale permeabilities require an interconnected fracture network of moderate conductivity with a relatively small spacing between fractures to obtain reasonable recovery factors. Microseismic mapping demonstrates that such networks are achievable and the subsequent production from these reservoirs supports both the modelling and the mapping. Tight gas sands, having orders of magnitude greater permeability than the gas shales, may be successfully depleted without inducing complex fracture networks, but other issues of damage and zonal coverage complicate recovery in these reservoirs. As with the shales, mapping has proved itself to be valuable in assessing the fracturing results. Introduction Unconventional reservoirs provide a significant fraction of gas production in North America and increasing amounts in some other regions of the world. Such reservoirs include tight gas sands, coalbed methane (CBM), and gas shales; in 2006 these reservoirs provided 43% of the US production of natural gas [Kuuskraa(1)]. Because of their limited permeability, which is foremost among many other complexities, some type of stimulation process (and/or dewatering in the case of CBM) is required to engender economic recovery from wells drilled into these formations. The focus of this paper is on gas shales, with particular emphasis on how these reservoirs perform relative to tight gas sands. The important role of natural fractures in both the stimulation and production processes, the importance of conductivity in the developed fracture or fracture system, and the critical influence of the matrix permeability are investigated using both mapping and modeling results.

BACKGROUND: Electron-beam CT (EBCT) quantification of coronary artery calcification (CAC) allows noninvasive assessment of coronary atherosclerosis. We undertook a follow-up study to determine whether CAC extent, measured at the time of angiography by EBCT, predicted future hard cardiac events, comprising cardiac death and nonfatal myocardial infarction (MI). We also assessed the potential of selected coronary artery disease (CAD) risk factors, prior CAD event history (MI or revascularization), and angiographic findings (number of diseased vessels and overall disease burden) to predict subsequent hard events. METHODS AND RESULTS: Two hundred eighty-eight patients who underwent contemporaneous coronary angiography and EBCT scanning were contacted after a mean of 6.9 years. Vital status and history of MI during follow-up were determined. Cox proportional hazards models were used to compare the predictive ability of CAC extent with selected CAD risk factors, CAD event history, and angiographic findings. Median CAC score was 160 (range 0 to 7633). The 22 patients who experienced hard events during follow-up were older and had more extensive CAC and angiographic disease (P<0.05). Only 1 of 87 patients with CAC score <20 experienced a subsequent hard event during follow-up. Event-free survival was significantly higher for patients with CAC scores <100 than for those with scores >/=100 (relative risk 3.20; 95% CI 1.17 to 8.71). When a stepwise multivariable model was used, only age and CAC extent predicted hard events (risk ratios 1.72 and 1.88, respectively; P<0.05). CONCLUSIONS: In patients undergoing angiography, CAC extent on EBCT is highly predictive of future hard cardiac events and adds valuable prognostic information.

Abstract Vertical fractures and horizontal fine layering combine to form a long, wavelength equivalent orthorhombic medium. Such media constitute a subset of the set of all orthorhombic media. Orthorhombic elastic symmetry is the lowest symmetry for which the slowness surface (the solution of the Christoffel equation) is bicubic rather sextic. Various properties of orthorhombic media, such as the number and location of conical points and longitudinal directions, may be derived from the slowness surface or, because of its bicubic character, the squared slowness surface, which is a cubic surface. From the occurrence and angular orientation of some of these distinctive features, conclusions can be drawn with respect to the properties of the medium and to the parameters of the assumed underlying causes of the anisotropy. The estimation of these more subtle properties gains greater importance with the proliferation of multiazimuthal seismic surveys and the ability to drill along ever more complicated 3-D well trajectories.

Abstract In March 2013, the world's first field trial of gas production from marine methane hydrate deposits was conducted in the Daini Atsumi Knoll area of the Eastern Nankai Trough off the Pacific coast of Japan as a process to bring gas hydrates under seafloor to valuable energy resource. The technique used to dissociate the ice-like material was "depressurization method" that had been applied in the previous production test in Mallik site, the Northwest Territories, Canada in 2007-2008. Japan Oil, Gas and Metals National Corporation (JOGMEC) as a part of MH21, the Research Consortium for Methane Hydrate Resources in Japan planed and supervised the project with the funding of the Ministry of Economy, Trade and Industry (METI), and scientific supports from the National Institute of Advance Industrial Science and Technology (AIST). One production well with two monitoring boreholes were drilled in the test site for the test. Along with the flow test operation, intensive data acquisition program was planned and implemented to understand behavior of methane hydrate dissociation- bearing sediments against depressurization. To realize high degree of drawdown in relatively shallow formation below deepwater, several downhole devices were designed and installed. The flow test started in the morning of March 12 and lasted until severe sand production forced to terminate the operation six days later. During the stable production term, gas flow rate was approximately 20,000m3 under atmospheric condition, and gas liquid ratio was larger than 100. A lot of data including formation temperatures, fluid pressure and temperature, and physical property changes in the formation were obtained. The data taken are under studies to verify applicability of the depressurization technique as a methane hydrate production technologies.

Abstract Porous media have properties with heterogeneities on several length scales. It is possible to build digital models of such properties. However these can be so detailed that a computing machine of the same power as that used to build the property model is not able to solve the fluid flow equations using standard discretisation methods—storage is needed for workspace, and the discrete equations have to be solved in a reasonable time. This paper reviews averaging techniques, devised to simulate large scale features of solutions without necessarily solving all the fine scale equations. Copyright © 2002 John Wiley &amp; Sons, Ltd.