- Home
- Conferences
- Conference Proceedings
- Conferences
54th EAEG Meeting
- Conference date: 01 Jun 1992 - 05 Jun 1992
- Location: Paris, France
- ISBN: 978-90-73781-04-7
- Published: 01 June 1992
1 - 20 of 405 results
-
-
3D Seismic: A strategic tool in exploration and production
More LessSince the first 3D survey seventeen years ago, Companies of the Shell Group have operated nearly 250 such surveys outside North America and, as non-operating partners, have been involved in many others . Managing safety and paying proper attention to environmental impact is in increasing challenge.
-
-
-
Comparison of seismic results after Dip and Strike acquisition
More LessModel studies have shown the advantage of acquiring seismic data parallel to the main tectonic directions or to lithological variations . For instance, for an imaging problem below a fault, if the acquisition is orthogonal to the fault plane, the seismic ray paths are crossing the fault and will be affected if the acquisition is parallel to the fault plane, all the-ray paths are in the same panel and wil] not be distorted . In the Jatter case, we therefore have better conditions for applying traditional processing tools and, more especially, for applying Normai (hyperbolic) Move Out .
-
-
-
Seismic acquisition in the vicinity of a large compressor plant
Authors R. A. Brook, D. L. Bremner and R. P. DartThe use of 3-D seismic in the exploitation of mature fields is betoming increasingly common . However, in many cases noise generated by oil field equipment compromises data quality . This paper describes a prospect that was considered a no record area within a 3 km radius of a large compressor plant . A noise study shows that witti careful parameter design and new recording techniques useful data can be collected witpin 200 m of the plant .
-
-
-
Design of 3D land acquisition in a structurally complex environment
Authors J. M. Mougenot, E. Robein, J. Ravat and A. MorashSince 1987, 3D seismics have been the main tool used by ELF AQUITAINE for exploration as well as for field development in the Pyrenees foothills (Aquitaine basin of South France) . The geological context made of very tectonized structures and the . rather poor signal/noise ratio at target depth (4500 m to 5500 m) have led to develop specific design tools for these 3D surveys .
-
-
-
Efficient 3D surveys in a jungle environment
Authors M. F. Bee, H. Supiyanto, J. M. Bearden and E. F. HerkenhoffFor the last fourteen years , Caltex Pacific Indonesia (CPI) has been acquiring 3-D data over existing production fields in the jungle and/or swampy environment of Central Sumatra , Indonesia . The recent years have seen an increase in 3 -D activity in CPI which has forced an evolution towards cost reduction without jeopardizing data quality. CPI has successfully developed 3-D acquisition techniques which are operationally feasible and economically attractive . This achievement is the result of careful planning to optimize field parameters, the use of a gapped inline swath geometry, an increase in the number of channels available for recording , an increase in the rintis (Jungle cutting for acces) and drilling effort, surveying with GPS, and radio shooting . This paper wilt describe the above techniques and their advantages it will also demonstrate that the 3-D data acquired is of high quality with uniform fold , good offset and azimuth distributions, and economically reasonable for the difficult environment .
-
-
-
Multidimensional seismic exploration and its first application results
Authors A. S. Kashik, V. KH. Kivelidi, D. P. Zemtsova and V. A. MilashinA further enhancement in the accuracy of the seismic explóration methods is associated witti the development of 4D and 5D technologies based on a rational integration of profile data witti borehole measurements for more detailed study of geologie features and for monitoring the wavefield parameters in the course of the reservoir development . Witti regard to onland operations, concurrent observat.ions in a number of Wells, with the shot point locations scattered over an area, will permit : a) depth of the subsurface survey to be enhanced by deeper placing both source and especially receiver locations, below the near-surface section which is narmally a severe filter for waves reflected from deeper interfaces ; b) velocity determination accuracy to be mach improved by processing data from individual Wells and by comparing the results in overlap zones ; c) time sections to be obtained from various depth levels ; d) reflection horizons to be correlated along profile lines and over an area
-
-
-
Luna-Hera Lacinia 3D case history: solving complex structures in presence of heavy operative constraints by combining different acquisition techniques
Authors L. Bertelli, A. Nicora and L. SalvadorThe Luna - Hera Lacinia - 3D survey (Offhore Calabria, Southern Italy) covers an area of about 180 square Kms and represents an excellent example of the integration of deep, shallow marine and land 3D acquisition techniques . The survey has been acquired as a "full 3D" on an area characterised by a complex marine and land morfology with serious land operating constraints and complex subsurface structures at a commercially acceptable cost. The target of the survey was to define the structural setting of the miocene reservoirs of Luna and Hera Lacinia gas-fields in order to optimize their development stage. Considering the difficulties, the survey initially required an adequate planning of the various stages of operation and following this a numerical simulation to evaluate its effectiveness .
-
-
-
Velocity errors in linearized elastic inversion
Authors A. de Nicolao and G. DrufucaErrors in velocity on the overburden produce depth errors in the target and also a distortion of behaviour of amplitude and phase versus offset . The paper presents a quantitative description of these effects for a simple Barth model using linearized roversion (De Nicolao et al ., 1991) . Even few percents of relative velocity error are very damaging to the results .
-
-
-
Velocity discrimination by differential semblance
Authors W. M. Symes and M. KernThis paper presents an algorithmfor estimation of seismic p-wave velocity from multioffset reflection seismograms . The algorithm optimizes a cost function, part of which is the mean-square error between predicted and data seismograms . It also includes a, differential measure of event semblance or coherente, whence its name : differential semlance optimization . Unlike other implemations of the mean-square error criterion, the differential semblance version retains sensitivity over a wide range of velocity models . We present some numerical evidente of this sensitivity, using an example drawn from the Marmousi model [1] . A previous implementation of differential semblance optimization for acoustic p-tau data and layered models has been applied with success to both synthetic and field data sets and has a complete mathematical justification [4] . Therefore a, subsidiary purpose of this paper is to demonstrate an implementation of differential semblance in a non-layered ("complex structure") context . We employ the perturbational (generalized Born, primaries-only) approximation to the 2D constant density acoustic model . The velocity is split into a smooth background velocity v and a rough (oscillatory) reflectivity r = ðv/v, the latter regarded as a perturbation of the former . Denote the seismogram (i .e . suite of shot gathers corresponding to shot positions x,) by S(v)(x,t, x). Note that S depends linearly on R and nonlinearly on v . Let Sdata devote a, data set to be inverted.
-
-
-
Linearized elastic inversion for multioffset marine seismic data
Authors D. Mace, A. Bourgeois, G. Etienne and V. RichardFor each shot s, the linearization consists in substituting the observed field Ps by the sum of the primary field Ps and of the scattered field ðPs where Ps corresponds to the non linear propagation in the reference medium m0 and ðPs is a linear function of the perturbation ðm which is computed from the Jacobian Js of the non linear operator at m0 . The process of linearization is associated with smalt perturbations.
-
-
-
Paraxial wave equation inversion with geometric constraints
By C. BunksThe paraxial wave equation is one of the most accurate pre-stack imaging tools for seismic data . It has been shown that pre-stack paraxial wave equation migration correctly images seismic data even for very complex velocity models (such as those containing caustics). Furthermore, the fact that the paraxial approximation yields a one-way wave equation is ideal for migration and imaging since in principle it does not generate reflections as do the acoustic and elastic wave equations. Nevertheless, the formulation and implementation of the paraxial wave equation give rise to some undesirable numerical artifacts.
-
-
-
Calculation of the differential semblance gradient
Authors M. Kern and W. M. SymesA major computational task in implementing the Differential Semblancce Optimization method (see the companion paper [2] for a presentation of the method) is an accurate computation of the gradient of the objective function. In this paper , we show how such a computation may be accomplished, and assess its accuracy on a representative example.
-
-
-
Determination of fresnel zones by traveltime inversion
Authors P. Hurbal, J. Schleicher, M. Tygel and C. HanitzschSeismic wave propagation in the high-frequency range is usually described by (zero-order ) ray theory. Its validity conditions are extensively investigated, e.g., by Kravtsov and Orlov (1990) . For finite frequenties a ray can only be viewed as a mathematical concept . There is a ( frequency-dependent) region in its vicinity that influences the wavefield received at the end of the ray . This region is the so-called (first) Fresnel volume of the ray . Any cross-section through it is a Fresnel zone. (Gelchinsky, 1985; Cerveny and Soares, 1992; Knapp, 1991) . In other words, the Fresnel volume is the envelope of all Fresnel zones along the ray. For seismic stratigraphic modeling, usually the Fresnel zone at the reflector is of interest, so as to know which part of it contributes to the reflected field . Fresnel zones are computed very efficiently by forward dynamic ray tracing through a known velocity model (Cerveny and Soares, 1992) . However, exploration geophysicists involved in a stratigraphic analysis would prefer to know the Fresnel zone of a reflecting interface without knowing the details of the reflector overburden, i .e., they are interested in solving an inverse problém . For a plane layered Barth model, it is possible to solve this inverse problem (i e., to calculate the Fresnel zone directly from measured traveltimes, e.g., Erom the rms-velocity) .
-
-
-
Nonlinear inversion of seismic reflection data: state-of-the-art
Authors A. Tarantola, M. Noble, C. Barnes, M. Charara, H. Igel, J. Lindgren, G. Röth and N. RoxisThere is little doubt that to extract a maximum of information from seismic data, one must try to fit the observed waveforms by synthetic waveforms, obtained through careful modeling of the propagation of seismic waves.
-
-
-
Nonuniqueness in nonlinear traveltime tomography
Authors J. R. Matarese, W. L. Rodi and M. N. ToksozMethods of crosswell tomography have focused largely on the construction of images of seismic velocity and little on the uncertainty, or nonuniqueness, of such images . In this paper we address the Jatter problem using a Backus-Gilbert methodology adapted to nonlinear inverse problems.
-
-
-
Borehole coupling effects on clamped geophone responses: experiments and theory
Authors M. H. Worthington, C. K. Jituboh, C. Chang and S. K. ChangSeismic waves detected by clamped geophones in a borehole can be affected by the borehole at high frequenties (Chang et al, 1989). A 20 cm diameter water filled borehole resonates in anti-syminetric mode at approximately 4 kHz and in symmetric mode at approximately 9 kHz. Below 2 kHz, the clamped geophone response is a combination of monopole, dipole and quadrapole vibirations in the borehole. To illustrate these effects, a, crosshole experiment was perfomed at the Imperial College borehole test site. Figure 1 Shows veldcity and gamma logs from the site and the source and receiver distribution in two, vertical holes. A three component clamped accelerometer was positianed at. 65m and 105m depth and detonators were fired at 5m intervals from 30m to 105m in the other Hole. The inter-hole spacing is 25m . The accelerometer was specifically designed to be free of resonances up to at least 2.5 kHz . Figure 2 (a.) and (b) show the recorded waveforms and the corresponding first arrival P wave hodograms from the radial and axial components of the accelerometer when positioned at 65m and 105m depth respectively. Depths in these figures refer to the positions of the source . The dominant frequency of these data. is at 1 kHz. Note that there is very little axial vibration when the source and the receiver are at approximately the same depth where as at, larger depth offsets, the hodograms are elliptical. It is conceivable that some hodogram ellipticity might result from interference between the direct and reflected or refracted waves within the multi layered medium. Full elastic wave finite difference modelling was perfomed with a model based on the borehole sonic and density logs. Hodograms calculated from these synthetic seismograms are shown in figure 2 (b) (labelled MODEL) and are seen to be essentially linear.
-
-
-
Borehole effects on downhole seismic measurements
Authors C. Peng, C. H. Peng and M. N. ToksozThere are increasing interests in acquiring crosshole and VSP surveys at frequency up to 1 kHz or more, with the intention to resolve the fine details of structures and lithology between Wells (Bregman et al ., 1989; Harris, 1988; Tura, 1991) However, at frequencies on the order 1 kHz, the existence of the fluid-filled borehole has a strong influence on the downhole measurements. Depending on the frequency and angle of incidence, as well as the formation properties, the measured displacements on the borehole Wall or pressure at the center of borehole may be significantly different from those of the incident wave. Without taking proper care of this effect, any imaging or inversion algorithm which utilizes both the amplitude and phase information of recorded energy will produce erroneous results.
-
-
-
Reservoir definition using triaxial walkaway VSPs
Authors K. J. Dodds, M. A. Jones, M. Idrees and W. S. LeaneyA gas discovery was made by British Gas with an exploration well in block 47/4b of the UK continental shelf. It was important to define the extern of the reservoir particularly to the North West . The structural history of this location is extremely complex, panicularly with respect to the near surface . Ray-path distortion through the complex overburden means conventional surface seismic data is of extremely poor quality, making interpretation difficult . British Gas embarked on an extensive walkaway and offset VSP program on well 47/4b- 5 The success of these surveys to image the Rotliegende azimuthally from the well was dependent on the ability of the processing to compensate for ray - path distortion together with a confident separation of shear and compressional components. The key step involved the extension of parametric inversion developed for VSP to walkaway geometry which resolved the raw triaxial data info its constituent wavefields (Fig 2). This allowed conventional migration with the 3D-lattice geometry to define the extent of the field (Fig 1 ).
-
-
-
Practical aspects of processing crosshole seismic reflection data
Authors P. S. Rowbotham and N. R. GoultyA crosswell seismic dataset was acquired by SERES at Scheemderzwaag in the Groningen gas field in late 1990 (see news item in First Break, September 1991, p401) . Recordings were made in Triassic and Zechstein strata around 2200-2600m depth, where the Wells are just over 300m apart. Stanford University's acquisition system was used, which has cylindrical piezoelectric Bender transducers as sources and receivers.
-
-
-
Reservoir monitoring using the VSP technique. A case study in the Oseberg field
Authors S. E. Johnstad and H. AhmedThe Oseberg Field is located in the Norwegian North Sea blocks 30/6 and 30/9, approximately 140 km northwest of Bergen with a maximum extension of 26 km north-south and a maximum width of 6 km east-west . The Field Game on stream in December 1988 . The Field comprises three major easterly rotated fault blocks Galled Alpha, Gamma and Alpha North . Hydrocarbons occur within the sandstones of the deltaic Middle Jurassic Brent Group . The reservoir sands exhibits excellent reservoir quality with porosities around 20-25% and permeabilities ranging up to several darcys . The structural dip is normally 6-10 ° east-northwest and the gross Brent thickness varies between 40 and 200 m .
-