Showing papers in "First Break in 2000"

Automatic seismic prediction ahead of the tunnel boring machine

Abstract: As the world's population grows, with rapid economic expansion, there is an increasing demand for better transport links to improve the mobility of goods and people. As a result more and more tunnels are being built. For example, at the turn of the year 1998/99 more than 200 kilometres of tunnel with a diameter over 1 m were under construction in Germany. About three-quarters of this kilometrage is built for road-or rail-based transportation systems. For economic and safety reasons an increasing portion of tunnels are nowadays drilled by tunnel boring machines (TBM's also called tunnelling machines), particularly in soft ground i.e. less consolidated sediments. For example, 11 TBM's have been employed to bore the 50.5 kilometre Eurotunnel between France and England which mainly passes through Lower Cretaceous chalk and clay. TBMs remove soil and rock from the tunnel face as the cutting wheel rotates and the machine pushes forward, In hard rock traditional drill-and blast still dominates over TBM, but in soft ground most tunnels today are bored by tunnelling machines.

Monitoring of water seepage from a reservoir using resistivity and self polarization methods: case history of the Petergoph fountain water supply system

Abstract: Petergoph, a suburb of Saint-Petersburg, was historically planned as a fountain centre similar to Versailles. The Petergoph fountain water supply system consists of artificial reservoirs formed by dams. Continued supply depends on the water level in the reservoir and the integrity of the dam. We used electrical methods for monitoring the stability of the reserve pond dam in this water supply system. Ogilvy et al.(1969) and Bogoslowsky & Ogilvy (1970a, b) used geophysical methods to investigate water leakages from reservoirs but did not use continuous observations. Their results therefore give only snapshots of the spatial distribution of dam parameters and do not characterize their temporal variation. We use two complete series of geophysical observations to monitor changes in the hydrogeological regime over a spring month, at the time of annual flood and just after.

Using neural networks to predict porosity thickness from 3D seismic

Abstract: This article describes the use of an artificial neural network to predict area-wide reservoir parameters by classifying multi-attributes derived from 3D seismic data. Special emphasis is placed on the comparison between the artificial neural network and geostatistical appoaches.

Crustal structure and evolution of the Carpathian‐Western Black Sea areas

Abstract: The Carpathian and Balkan foldbelts are segments of the Tethyan chain, emplaced and deformed during the Mesozoic and Cenozoic. Their foreland, situated around the western Black Sea, consists of several platforms and the North Dobrogea-South Crimea Cimmerian Chain (Figure 1).

Depth imaging and velocity calibration by 3D adaptive tomography

Abstract: Reflection tomography is an effective technology for reconstructiong a macro-model of the Earth, i.e. its major velocity anomalies and reflectors, especially in complex 3D geological structures. After the pioneering papers of Gjoystdal & Ursin (1981) and Bishop et al. (1985), traveltime inversion of reflected and refracted arrivals has been used to improved static corrections and near-surface imaging. The authors of this article have processed a data set over important producing fields which was acquired by OMV in the Vienna Basin, between Vienna and the border with the Slovak Republic. The tectonic complexity of the area, with major faults and static problems, made this data set a severe test of the robustness of the algorithms they have developed.

Coherent noise attenuation using Inverse Problems and Prediction Error Filters

Abstract: Two iterative methods that handle coherent noise effects during the inversion of 2-D prestack data are tested. One method approximates the inverse covariance matrices with PEFs, and the other introduces a coherent noise modeling operator in the objective function. This noise modeling operator is a PEF that has to be estimated before the inversion from a noise model or directly from the data. These two methods lead to Independent, Identically Distributed (IID) residual variables, thus guaranteeing a stable convergence of the inversion schemes and permitting coherent noise filtering/separation.

Velocity inversion in the Lodhika area, Saurashtra peninsula, Western India

Abstract: Refraction seismic surveying was the first major geophysical method to be applied in the search for oil-bearing structures. Today, however, oil exploration relies almost exclusively on near-vertical reflection technology. Yet, refraction surveying, as it has a number of important advantages, is still occasionally used in oil exploration, particularly where it can assist in resolving complicated problems in structural geology.

Resistivity imaging of shallow salt with magnetotellurics as an aid to prestack depth migration

Abstract: Currently NAM (Nederlandse Aardolie Maatschappij B.V.) is undertaking a large Pre-Stack Depth Migration (Pre-SDM) campaign over several salt-related prospects in the Netherlands, two of which, Broek and Ommelanderwijk, are located in fig. 1. To build proper Pre-SDM models of salt domes it is essential to have accurate knowledge of the geology in the shallow subsurface. Using data acquired in a conventional 3D seismic acquisition geometry, with typical 400-500 m line spacing, it is often difficult to image the top of shallow salt domes accurately in the 0-500 m depth range. This problem can be seen clearly in Fig. 2, where a seismic section through the Broek salt dome is displayed.

Statfjord study demonstrates use of neural network to predict porosity and water saturation from time-lapse seismic

Abstract: With an estimated STOIIP of more than 1 billion m3, Statfjord is the largest oil discovery in the North Sea to date. Structurally the field is a tilted fault block with Jurassic beds dipping westward at 6 to 8° and truncated on the faulted and eroded East flank (Kirk, 1980 and Fig. 1). The field is divided into three main reservoir units, which are in order of decreasing importance: Brent, Statfjord and Dunlin. Since its discovery in 1974 almost 200 wells have been drilled. The cumulative production from the start of production in 1979 until the end of 1997 was 550 million m3. This represents approx. 55% of the initial oil in place and 83% of the official recoverable reserves of 662 million m3. All reservoirs have been partly drained so far during the field's history. In the early years, produced gas was reinjected into the Statfjord reservoir at an up dip position, while the Brent reservoir was depleted until pressure maintenance by down flank water injection was established in 1986. This resulted in extensive gas and water breakthroughs in the production lines and a change in drainage strategy. In the last decade the strategy has been based on in-fill drilling to produce by-passed oil and remaining oil in structural traps and recently in combination with gas and water injection to mobilize remaining oil. To find unswept or by-passed oil three consecutive 3D seismic surveys, acquired in 1979, 1991 and 1997 respectively, have been the basis for seismic monitoring analysis. In this case study, only the latter two surveys were used. The aim of the study was to predict porosity and water saturation at the respective acquisition dates. For each survey five seismic volumes were available: mid- and far-angle reflectivity, mid- and far-angle elastic impedance, and acoustic impedance. The partial stacked cubes have similar fold and contain angles around 15 and 25°, respectively. The inversion method used was a global search through a simulated annealing scheme using a constant wavelet. Some 130 wells were used, each with an extensive suite of measured logs and 1991 and 1997 timeequivalent logs. The reservoir simulator and a modified Gassmann fluid replacement algorithm were used to compute the time-equivalent logs. For most wells a neural network predicted a measured shear sonic log from measured sonic, density and gamma ray logs.

Potential power in the application of seismic volume attributes

Abstract: Henning Trappe, Carsten Hallmich and Marc Foell from the German company Trappe Erdoel Erdgas Consultant (TEEC) present their ideas on seismic volume attributes. They claim that these methods are much more powerful than just mapping subtle lineaments.

The effect of acquisition direction on preSDM imaging

Abstract: A production 3D preSDM project from the southern North Sea using several vintages of input data was run using a velocity-depth model common to the whole area, with good final results. The expected progressive improvement from postSTM to postSDM to pre SDM was demonstrated for the target horizons. As a seperate study to the production project, we undertook to investigate the effect of acquisition direction on final image quality. To achieve this, we selected two vintages of data which were shot orthogonally to one another, but which otherwise had the same acquisition parameters. These data had sufficient overlap to permit full imaging in the area under investigation. Ray trace studies were performed to assess the effects of target illumination from the dip-shot and the strike-shot surveys. Using the actual recorded navigation positions from the two surveys, 3D two-point finite offset ray tracing was performed using a common model.

Seismic penetration problem in the Wadi Field, Sirte Basin, Libya

Abstract: The Wadi Field is located within the north central part of the Sirte basin, Libya. Over the past few years, Sirte Oil Company of Libya has acquired several seismic surveys in this area. The latest survey was an experimental line shot in 1995, with five heavy vibrators sweeping over the bandwidth 8-40 Hz and 720 recording channels. The objective was to obtain interpretable information beneath the top Upper Cretaceous horizon (top Kalash) which is generally the lowest horizon visible on the processed seismic sections. The primary exploration target is the Nubian formation within the Lower Cretaceous. The acquired dataset was processed by COG in 1996, and subsequently reprocessed by me as part of this project. Some improvement in the static corrections is evident in the reprocessed data, but neither processing sequence was successful in delineating the oil-bearing structure within the Lower Cretaceous. The rest of the project was an investigation into the reasons for the lack of signal penetration beneath the top Kalash horizon. Synthetic seismograms were generated using sonic log data from well D7-NC149 to understand the effects of the primary reflectivity, transmissivity, and multiples on the primary reflection events in general and on signal returns from the target horizon in particular. The behaviour of the reflectivity at the top Kalash and the top Nubian horizons and the transmission losses within the geological sequence overlying these horizons were examined in both time and frequency domains. Spectral analysis was conducted for 64-sample windows around the two-way travel times of both horizons in order to understand the effect of each factor separately.

Peruvian cruise provides fresh insights into gas hydrates

Abstract: Edited report from co-chief scientists Jorg Bialas of GEOMAR, Kiel and Nina Kukowski, GFZ, Potsdam on a geophysical acquisition campaign offshore Peru on board the RV Sonne to investigate the Peruvian convergent margin, its structure, geodynamics and gas hydrate systems.

Prospects for activity levels in the UKCS

Abstract: We present here edited notes and revealing, if somewhat pessimistic, illustrations on future projections of UK oil and gas E&P activity in the years to come from the presentation by Prof Alex Kemp, Professor of Petroleum Economy, Aberdeen University. The conclusion from the data presented was that the UK will in less than five years be facing a sharp decline in offshore activity caused to a large extent by factors beyond the control of a single country.

Integrated seismic exploration for mine planning and profitability

Abstract: High-resolution seismic exploration techniques, including surface reflection and in-seam seismic, are now accepted as a powerful aid to coal mine planning, the in-seam seismic method being generally considered a tactical tool, and the surface reflection method a strategic tool. In-seam seismic has been described by Jackson (1985) and the surface seismic reflection method as applied to the coal mining industry has been examined in case histories by Fairbairn et al. (1986). This paper discusses the impact of seismic exploration from 1977 to the present day on the development of an underground mine layout, and the accuracy of those seismic interpretations after underground proving. The paper also discusses the added benefits of an integrated surface and underground seismic exploration programme, examining the uses and constraints of each and showing how the two techniques complement each other.

Evolution of a seismic acquisition methodology through integrated testing - onshore Abu Dhabi, United Arab Emirates, 1996-2000

Abstract: Summary For onshore seismic data the resolution at the exploration target level depends on the complex interaction of many factors. These include the survey environment, geology, acquisition configuration and data processing procedures. When designing seismic surveys we wish to achieve the required target level resolution while minimising both cost and risk. For Vibroseis surveys, the time expended recording each source point, called the sweep effort/VP, can be a key cost factor. Uncertainty about the impact of differing options for the acquisition geometry and source point sweep effort on the target level resolution represents a risk factor. A 3D seismic exploration methodology driven by the resolution at the target level has been implemented for onshore Abu Dhabi, United Arab Emirates, by the Abu Dhabi Company for Onshore Operations (ADCO), in co-operation with Western Geophysical. Techniques originally developed for the on-crew processing of 2D acquisition parameter tests have been extended to 3D. Integrated data acquisition and processing tests provide fully processed, 3D migrated data volumes. Test analysis is based on the interpreted resolution at the target level, allowing direct judgements on key parameters affecting data cost and quality. The spatial distribution of source energy, improving the trace offset distribution and increasing the CMP fold is seen as significantly more important than the sweep effort/VP. Close co-operation between ADCO and Western's Geophysical Abu Dhabi data acquisition and processing staff ensure that complex data manipulation issues are handled in a timely manner, allowing the results of the testing to influence an ongoing 3D project. Use of this methodology has so far provided both improvements in data quality to levels not seen before for Abu Dhabi onshore data while simultaneously reducing the cost and risk of data acquisition. This paper summarises results from some of the key events in the development of the acquisition testing methodology: (A) 1996 – 2D testing for 2D acquisition. (B) 1997 – 2D testing for 3D acquisition. (C) 1998 – Simultaneous downhole acquisition. (D) 1999 – 3D testing for 3D acquisition.

Fibre optic sensor technology could offer way forward for reservoir monitoring

Abstract: BP's new agreement to invest in fibre optics suggests that the technology may have arrived. Andrew McBarnet reports.

3D design symposium

Abstract: For the workshop '3D Seismic surveys: design, tests and experience' held at the 61st EAGE Conference on 5 June 1999, five specialists in the design of 3D surveys were invited to recommend survey design parameters, based on a common case study. Participants were Mike Galbraith (Seismic Image Software), Malcolm Lansley (Western Geophysical), Julien Meunier (CGG), David Monk (Apache Corporation) and Jim Musser (Gren Mountain Geophysics). Their recommendations are reproduced in the articles following the introductory paper.