Seismic Borehole Research Articles

Contribution à l'étude d'une partie du bassin d'Essaouira (Maroc) par sismique réflexion

Abstract A large number of seismic reflection lines and boreholes have been carried out in the Essaouira Basin by the oil industry. The present study concentrates on the reinterpretation of these data in the restricted area of Khemis Meskala, in order to better characterise the structure of the Cretaceous aquiferous system. The reflector corresponding to the bottom of the Vraconian formation has been identified on the different seismic sections. This horizon, which marks the base of the aquiferous system, was first digitised on time migration sections and then converted to depth sections using a suitable linear velocity law. The isobath map of the bottom of the Vraconian resulting from this study images the 3D geometrical structure of this horizon and shows that it is slightly folded in domes and basins. This document will be useful for rationalising the future hydrogeological researches that will be undertaken in the Khemis Meskala area. To cite this article: M. Jaffal et al., C. R. Geoscience 334 (2002) 229–234.

GEOTECHNICAL AND GEOPHYSICAL DESCRIPTION OF EURO-SEISTEST, USING FIELD, LABORATORY TESTS AND MODERATE STRONG MOTION RECORDINGS

EURO-SEISTEST is a European test site established in the Mygdonian basin, near Thessaloniki, in Northern Greece. Its aim is to allow detailed and well documented studies in many fields of engineering seismology, earthquake engineering, soil dynamics and seismology. Theoretical and experimental seismic ground response analysis along the valley is one of the most important tasks of the project. The very detailed knowledge of the geological and geotechnical structure of the site as well as numerous data from a continuous seismological and geodetical survey and dense semi-permanent and permanent instrumentation, offer the possibility of conducting detailed empirical and theoretical studies on the effects of surface geology on seismic ground motion. EURO-SEISTEST is a unique test site for checking the reliability of existing theoretical models of site effects, to develop new ones, ana to interpret the physics of seismic ground response. The paper presents: (a) the general layout of the test site, (b) the main results of the extensive geophysical and geotechnical surveys, to determining the geometry and the dynamic properties of soil formations, and (c) the validation of valley's structure with instrumental estimates of the site effects along the valley. Emphasis is given to comparisons and correlations between results derived from different methods of seismic prospection (refraction, surface wave inversion, borehole seismics) and geotechnical in situ tests. In order to better constrain the structure of the valley and the dynamic properties of the soil formations, specific criteria and procedures are developed for soil characterisation.

Seismic reflection and borehole geophysical investigations in the Matagami mining camp

A high-frequency vibroseis seismic survey was conducted by Lithoprobe across a well-known section of the Matagami mining camp to assess the usefulness of seismic methods in lithological mapping. The data have been reprocessed to enhance shallow reflections. Critical processing steps for the preservation of the shallow features include refraction static corrections, cross-dip corrections, and first break mutes. The seismic data were calibrated using geophysical logs from two boreholes adjacent to the profile. Physical rock property measurements suggest that strong reflectivity within the volcanic sequence occurs at rhyolite-gabbro contacts. The Lower Wabassee Group, a sequence of gabbros and basalts with interlayered rhyolite horizons, has been identified as a seismic marker. This reflective package overlays the horizon where most sulphide deposits are known to be located. In the Matagami mining camp, seismic reflection methods can be used to map the deep volcanic stratigraphy and structures.

Seismic tomography using borehole experiments: Examples from Mars and Auger in the deepwater Gulf of Mexico

In the period 1989–91, Shell Offshore acquired several walkaway VSP surveys as part of the evaluation program for development wells in the Mars and Auger areas in the deepwater Gulf of Mexico. Since both fields lie near salt, understanding the salt geometry is critical in the search for additional reserves that are difficult, if not impossible, to detect with standard surface seismic.

Seismic reflection and borehole geophysical investigations in the Matagami mining camp

Seismic reflection and borehole geophysical investigations in the Matagami mining camp

Borehole Seismic Interpretaton in the Workstation Environment: ABSTRACTS

Borehole Seismic Interpretaton in the Workstation Environment: ABSTRACTS

Petroleum Exploration Risk Reduction Using New Geoscience Technology

As economics of the oil and gas industry become more restrictive, the need for new means of improving exploration risks and reducing expenses is becoming more acute. Partnerships between industry and academia are making significant improvements in four general areas: Seismic acquisition, reservoir characterization, quantitative structural modeling, and geochemical inversion. In marine seismic acquisition the vertical cable concept utilizes hydrophones suspended at fixed locations vertically within the water column by buoys. There are numerous advantages of vertical cable technology over conventional 3-D seismic acquisition. In a related methodology, ‘Borehole Seismic,’ seismic energy is passed between wells and valuable information on reservoir geometry, porosity, lithology, and oil saturation is extracted from the P-wave and S-wave data. In association with seismic methods of determining the external geometry and the internal properties of a reservoir, 3-dimensional sedimentation-simulation models, based on physical, hydrologic, erosional and transport processes, are being utilized for stratigraphic analysis. In addition, powerful, 1-D, coupled reaction-transport models are being used to simulate diagenesis processes in reservoir rocks. At the regional scale, the bridging of quantitative structural concepts with seismic interpretation has lead to breakthroughs in structural analysis, particularly in complex terrains. Such analyses are becoming more accurate and cost effective when tied to highly advanced, remote-sensing, multi-spectral data acquisition and image processing technology. Emerging technology in petroleum geochemistry enables geoscientists to infer the character, age, maturity, identity and location of source rocks from crude oil characteristics (‘Geochemical Inversion’) and to better estimate hydrocarbon-supply volumetrics, which can be invaluable in understanding petroleum systems and in reducing exploration risks and associated expenses.

An interpretation of the gravity anomaly at Warlingham, Surrey

AbstractAn interpretation of the negative gravity anomaly at Warlingham, Surrey, controlled by a seismic reflection profile and several boreholes, suggest that it may be caused by a wedge-shaped body of lowdensity Upper Palaeozoic rocks. The seismic reflection data suggest that the upper boundary of the body may be thrust-controlled and originated during Variscan compression. The location of the thrusting appears to be controlled by the southern margin of the stable London Platform. Comparison with similar structures of this type elsewhere suggests that the Variscan Front in this area lies just to the north of Warlingham.

NEW DIRECTIONS IN GEOSCIENCE TECHNOLOGY FOR PETROLEUM EXPLORATION IN THE NEW AGE

As economics of the oil and gas industry become more restrictive, the need for new means of improving exploration risks and reducing expenses is becoming more acute. Partnerships between industry and academia are making significant improvements in four general areas: Seismic acquisition, reservoir characterisation, quantitative structural modelling, and geochemical inversion.In marine seismic acquisition the vertical cable concept utilises hydrophones suspended at fixed locations vertically within the water column by buoys. There are numerous advantages of vertical cable technology over conventional 3-D seismic acquisition. In a related methodology, 'Borehole Seismic', seismic energy is passed between wells and valuable information on reservoir geometry, porosity, lithology, and oil saturation is extracted from the P-wave and S-wave data.In association with seismic methods of determining the external geometry and the internal properties of a reservoir, 3-dimensional sedimentation-simulation models, based on physical, hydrologic, erosional and transport processes, are being utilised for stratigraphic analysis. In addition, powerful, 1-D, coupled reaction-transport models are being used to simulate diagenesis processes in reservoir rocks.At the regional scale, the bridging of quantitative structural concepts with seismic interpretation has led to breakthroughs in structural analysis, particularly in complex terrains. Such analyses are becoming more accurate and cost effective when tied to highly advanced, remote-sensing, multi-spectral data acquisition and image processing technology. Emerging technology in petroleum geochemistry, enables geoscientists to infer the character, age, maturity, identity and location of source rocks from crude oil characteristics ('Geochemical Inversion') and to better estimate hydrocarbon-supply volumetrics. This can be invaluable in understanding petroleum systems and in reducing exploration risks and associated expenses.

An Overview of Southern California Crustal Deformation Studies and Their Tectonic Interpretation: ABSTRACT

Geodectic studies, particularly the high-accuracy results obtained from Global Positioning System (GPS) data, have helped to define the active tectonics of the western Transverse Ranges. Recent results of the Transverse Ranges Experiments (TREX) and related work have documented revisions to earlier published reports on crustal deformation in the region. A review of the earliest to the most recent geodectic results will be followed by a summary of the currently documented rates and styles of deformation. Also, the latest findings from work in the Los Angeles region will be discussed. A challenging aspect of geodectic work is to convert the displacement vectors obtained into, for example, slip rates that are useful as inputs to tectonic or seismic hazard models. Because the faults under study are generally locked to depths of 10 to 20 km, modeling is required to interpret the observed displacement field. The related problems and limitations inherent in obtaining equivalent fault slip rates from a displacement field map will be discussed, and a range of plausible models investigated for the Los Angeles region. Without accurate information on the geometry of faulting at depths >10 km, where interseismic slip occurs, many fault slip models are tenable. Because of this, themore » interpretation of geodectic data in terms of slip rates on active faults will continue to rely in turn on interpretations of deep structures that are based on seismic images, borehole, and surface geological data. It is hoped that resolution of controversies over the nature of deep structure in the western Transverse Ranges will coincide with the development of a more complete geodetic picture of ongoing deformation, and that cooperative work can then lead to a greatly improved seismic hazard model for the region. In the meantime, geodectic information can provide among the strongest constraints on expected moment rate, for computing seismic hazard in areas of blind' or widely distributed faulting.« less

New Dimensions in Geophysics for Reservoir Monitoring

Summary Advances in geophysical survey techniques have improved surface and borehole methods used for reservoir delineation and description. These same techniques can be used to map changes in reservoir conditions caused by various types of reservoir flooding. This paper discusses reflection and borehole seismic techniques and borehole electrical methods used for secondary and tertiary recovery. The unique aspect of geophysical monitoring is that the surveys are repeated during field development, so changes in geophysical response can be observed. These data can be interpreted by reservoir geologists and engineers to reveal the distribution of the production process and then used in production planning.

Crustal Structure and Tectonic Evolution of the Potiguar Basin--Northeast Brazil

The combined analysis of potential field and seismic reflection data suggest that the Potiguar basin of northeast Brazil developed as a consequence of northwest-southeast extension, resolved in the upper crust by hanging-wall block rotation along a system of linked faults. This extension developed during the Early Cretaceous rifting associated with the separation of South America and Africa. The basic basin architecture includes two main parallel northeast-trending half-grabens (Umbuzeiro and Boa Vista) separated by intervening basement highs and northwest-trending transfer faults. A three-dimensional crustal-scale model of the basin was generated by combining deep and shallow seismic reflection data, borehole and outcrop information, and potential field data. The deep seismic profiles reveal a highly reflective crust underlain by a high-amplitude reflection Moho around 10 seconds (roughly 30 km depth). Moreover, it seems that the basin-bounding normal faults terminate at a mid-crustal detachment surface, suggesting that the basin architecture is mainly controlled by two parallel listric normal fault ones that follow pre-existing upepr crustal weaknesses, partially reactived during the main rift episode (Neocomian). Whereas the pre-existing northeast-trending planar fabrics within the basement (schistosities, gneissosity, and shear zones) apparently controlled the main normal faults, internal conjugate and synthetic transfer faults are probably related tomore » major discontinuities in basement rock fabrics. Seismic reflection data together with gravity and magnetic modeling, show that the basin architecture is directly related to a linked system of northeast-trending listric normal faults and a mid-crustal detachment surface.« less

Combined processing of seismic reflection and borehole measurements in the Moroccan basin offshore NW-Africa at DSDP-site 416

The Ocean Drilling Program (ODP), and its predecessor DSDP, collected a unique data set which can be used to verify fundamental hypotheses on the origin and constitution of the oceanic crust.

Application of Sequence Stratigraphy to Oil and Gas Exploration in Bredasdorp Basin, Offshore South Africa: ABSTRACT

For more than two decades, oil and gas exploration in offshore South African rift basins within structural synrift plays yielded limited success. After the first oil discovery in postrift sediments in the Bredasdorp basin in 1987, sequence-stratigraphic concepts were applied to the Lower Cretaceous postrift sequences to permit correlation of depositional systems tracts and related facies throughout the basin. Extensive high-resolution seismic coverage and borehole control supported the study. The interplay of diminishing rift tectonics, thermal cooling, and inferred eustatic variations in global sea level produced a distinctive series of repetitive cycle depositional sequences. As many as 10 cyclic sequences and megasequences, deposited between the mid-Valanginian and lower Santonian, can be recognized within resolution limits of regional seismic profiles. Various elements of lowstand systems tracts within these sequences appear to contain potential reservoirs. Highly erosional (type 1) unconformities, commonly exhibiting incised valleys and canyons, provide surfaces on which (1) mounded and sheetlike submarine/basin-floor fans, (2) submarine channel fill and associated mounds and fans, and (3) prograding deltaic/coastal lowstand wedges were deposited. These fans, channel fills, and wedges are top sealed and sourced by transgressive shales and marine condensed sections, deposited at a time of regional transgression of the shoreline. Onemore » discovery well and various reservoir-quality sandstones occurring at predicted stratigraphic levels in other wells support the application of the sequence-stratigraphic concepts to hydrocarbon exploration.« less

EXPERIMENTAL COMPARISON BETWEEN SPECTRAL RATIO AND RISE TIME TECHNIQUES FOR ATTENUATION MEASUREMENT*

ABSTRACTTwo techniques for the measurement of attenuation–spectral ratio and rise time techniques–were tested and compared in the laboratory. The spectral ratio technique proved to be reliable and easy to implement for intermediate values (5 < Q < 50) of attenuation. For low (Q > 50) and high attenuations, the spectral ratio technique is inaccurate. Calculating the rise time on simulated signals, we found a relation between rise time τ and the ratio travel‐time to quality factor T/Q which could be approximated in intervals by the linear relation τ=τ+C*T/Q. The constants τ and C depend on the absolute value of T/Q and on the initial source signal. The rise time technique, performed on the first quarter period of the signal, enables high attenuations (Q < 5) to be measured. The determination of the relation between τ and T/Q is possible if one knows the initial source. We theoretically approximate this relation through a simulation using a realistic propagation model. With laboratory measurements made on Fontainebleau sandstone, we show that the rise time technique using the theoretical relation τ=τ(T/Q) gives comparable values of Q to those obtained from the spectral ratio technique. In borehole seismics, where it is often difficult to remove undesired signals, the rise time technique applied with the right (τ, T/Q) relation is the best method to use.

Seismic borehole tomography—Measurement system and field studies

A system for seismic tomographic measurements is presented, and both hardware and software are described. The system is intended to operate in the distance range 100-1000 m. An explosive source is used to generate signals which are picked up by receivers at the surface and in boreholes. Tomographic results from two field experiments are presented. The first experiment concerns mapping of an ore body in a mine, whereas the second concerns rock quality determination.

Correction to "Seismic borehole tomography—Theory and computational methods"

Correction to "Seismic borehole tomography—Theory and computational methods"

Determining Acoustic Velocity of Subsurface Formations From Well Log Data

For engineering, geophysical, and geological purposes, accurate formation velocities must be secured in areas where acoustic parameters have not been defined. Methods and techniques are discussed for correcting inaccurate well log data and for estimating velocities reliably as a function of other parameters . When acoustic values are available, cross sections and maps parameters . When acoustic values are available, cross sections and maps that require such information can be constructed. Introduction A special session on geophysics and petroleum engineering was held at the 1977 SPE-AIME Annual Fall Technical Conference and Exhibition. As the synergism between these disciplines grows, the use of subsurface information to calibrate and interpret seismic information will increase. Of particular interest are the quantity and quality of velocity information available from well logs. Acoustic velocity information is required when predicting the seismic character of subsurface formations and for translating the position of subsurface zones from depth (the engineering frame of reference) into time (the geophysical frame of reference).Many difficulties are encountered. Both well logs and seismic records vary from the measurement of absolute values and, as previously stated, their references are not the same. Altered rock types, damaged wellbores, and equipment-related spacing problems are obvious immediately and have been problems are obvious immediately and have been noted often. Unfortunately, continuous acoustic velocity log coverage exists for only a small percentage of all the wells ever drilled. Acoustic logging did not come into common use until 1957. The major service companies estimate that even today acoustic logs are run on only 40% of new wells, and no more than a small fraction of these have top-to-bottom coverage. By 1965, the gamma-gamma density log had become a routine service in the industry, and because it proved to be a superior porosity log in many provinces, the use of acoustic logs for evaluation (and consequently the gathering of velocity information) actually may have declined. Consequently, the determination of accurate formation velocities is not always straight-forward, even when subsurface information is available.Although seismic and wireline borehole methods use different sampling techniques and examine different volumes, the various measurements can be resolved to provide applicable comparative results. Formation velocities can be obtained from well log data by several methods. Acoustic Well Logs Conventional Acoustic Devices Standard spacings and configurations are engineered to minimize extraneous effects and to provide an optimum response for deriving petrophysical properties (porosity, shaliness, the percentage of oil properties (porosity, shaliness, the percentage of oil or gas, etc.) of formations in a liquid-filled borehole. For seismic comparisons, the logs must be edited and corrected to eliminate those effects that do not provide meaningful data. The lack of such data has provide meaningful data. The lack of such data has necessitated the development and use of alternative approaches for seismic problems. One alternative is the long-spaced sonic log. JPT P. 1453

Tektonische Auswertungen von seismischen Profilen und Bohrungen im Ruhrkarbon

Tektonische Auswertungen von seismischen Profilen und Bohrungen im Ruhrkarbon

Seismic study of the sediments in the Hudson River

Seismic refraction and borehole data obtained in the Hudson River near Nyack, New York, have shown that two horizons of unconsolidated sediment lie above the Triassic sandstone. The lower horizon, made up of unsorted clastic material, has a compressional velocity slightly greater than that of the water, whereas the upper layer, composed mainly of organic silt, has a compressional velocity less than half as great. During a seismic refraction experiment, two prominent wavetrains were recorded: a high-velocity leaking mode and a very slow, long-period normal mode which has been called the ‘Granddaddy’ wave. The dispersion of the latter is controlled primarily by the shear velocity structure of the organic silt layer. Analysis of the dispersion shows that the shear velocity in the organic silt increases rapidly with depth immediately below the river bottom and more gradually at greater depth in the layer. The final model obtained fits seismic and borehole data and appears to represent reasonable variations of the physical properties of the sediments.