3D Seismic Survey Research Articles

Characterization of mass transport deposits using seismic attributes: Upper Leonard Formation, Permian Basin

The Permian Basin is a structurally complex sedimentary basin with an extensive history of tectonic deformation. As the basin evolved through time, sediments dispersed into the basin floor from surrounding carbonate platforms leading to various mass movements. One such mass movement is observed on a 3D seismic survey in the Upper Leonard interval (Lower Permian) of the Midland Basin that is characteristic of a mass transport deposit (MTD). The 350 ft thick MTD mapped in the study area is 5 mi wide, extends up to 14 mi basinward, and covers only the translational and compressional regime of the mass movement. A unique sedimentary feature, unlike those observed previously, is mapped and interpreted as gravity spreading. MTDs have been extensively studied in the Delaware Basin of Permian-aged strata; however, only a few works have been published on the geomorphological expression of MTDs using seismic and seismic attributes to delineate the shape, size, and anatomy of this subsurface feature. The MTD in the study area exhibits an array of features including slide, slump, basal shear surface, and MTD grooves. In cross section, the MTD is characterized as chaotic with semitransparent reflectors terminating laterally against a coherent package of seismic facies, or the lateral wall. Sobel filter-based coherence, structural curvature, dip magnitude, and dip azimuth attributes are used to map thrust faults within the discontinuous MTD. Kinematic evidence provided by the Upper Spraberry isopach suggests that this MTD was sourced north of the Midland Basin and deposited on the basin floor fairway. Slope strata are interpreted from well-log analysis showing MTD as a mixture of carbonates and siliciclastics with a moderate to high resistivity response.

Pre and Post-Stack Imaging of 2D Seismic Data Using Time Migration for Ajeel Oil field, Central of Iraq

Kirchhoff Time migration was applied in Pre and Post-Stack for 2D seismic survey for line AJ-99N, that is located in Ajeel oilfield in Salah Al-Din Governorate, Central Iraq. The process follows several accurate steps to reach the final time migration stage. The results of applied time migration give an accurate image for the Ajeel anticline reservoir and to improve the signal to noise ratio. Pre-Stack shows a clearer image for the structure in the study area, and the time-frequency analysis insure the result.

Rock physics of the Wolfcamp Formation, Delaware Basin

Production from wells in organic-rich shales often shows considerable lateral variation. Reliable predrill methods to characterize the lateral heterogeneity of such reservoirs are required to optimize the trajectory of lateral wells in these low-permeability reservoirs. Petrophysical interpretation of measured well logs provides information on mineral, porosity, and kerogen content. Combining the results of petrophysical analysis with P-wave, S-wave, and density logs allows generation of a probability density function (PDF) for each of the different significant lithofacies. The PDFs are applied to the P- and S-impedance from prestack seismic amplitude variation with offset inversion to predict the spatial variation in the distribution of lithofacies and associated probability for the Wolfcamp Formation in an area covered by a 3D seismic survey in the Delaware Basin, West Texas. An anisotropic rock-physics model for the Wolfcamp Formation allows the effect of complex mineralogy, organic carbon concentration, and porosity on the P- and S-impedance to be investigated. Kerogen inclusions and pores act to increase Thomsen’s anisotropy parameter [Formula: see text] relative to [Formula: see text], and there is a competition between clay matrix anisotropy and inclusion shape anisotropy in determining the anisotropy of the rock. Inclusions with isotropic elastic properties act to decrease the anisotropy due to the dilution effect, but this decrease is partially offset by the increase in anisotropy due to the anisotropic shape of the inclusions. Application of the model to the determination of minimum horizontal stress indicates that kerogen-rich siliceous shales have the lowest value of minimum horizontal stress, whereas silica-rich calcareous shales, mixed siliceous shales, and clay-rich siliceous shales have higher values and may therefore act as barriers for the vertical growth of hydraulic fractures.

Wavelet transform‐based seismic facies classification and modelling: application to a geothermal target horizon in the NE German Basin

ABSTRACTAt the geothermal test site near Groß Schönebeck (NE German Basin), a new 3D seismic reflection survey was conducted to study geothermal target layers at around 4 km depth and 150°C. We present a workflow for seismic facies classification and modelling which is applied to a prospective sandstone horizon within the Rotliegend formation. Signal attributes are calculated along the horizon using the continuous Morlet wavelet transform. We use a short mother wavelet to allow for the temporal resolution of the relatively short reflection signals to be analysed. Time‐frequency domain data patterns form the input of a neural network clustering using self‐organizing maps. Neural model patterns are adopted during iterative learning to simulate the information inherent in the input data. After training we determine a gradient function across the self‐organizing maps and apply an image processing technique called watershed segmentation. The result is a pattern clustering based on similarities in wavelet transform characteristics. Three different types of wavelet transform patterns were found for the sandstone horizon. We apply seismic waveform modelling to improve the understanding of the classification results. The modelling tests indicate that thickness variations have a much stronger influence on the wavelet transform response of the sandstone horizon compared with reasonable variations of seismic attenuation. In our interpretation, the assumed thickness variations could be a result of variable paleo‐topography during deposition of predominantly fluvial sediments. A distinct seismic facies distribution is interpreted as a system of thicker paleo‐channels deposited within a deepened landscape. The results provide constraints for the ongoing development of the geothermal test site.

Using jittered sampling in designing geometry and imaging in shallow 3D seismic surveys

ABSTRACTWhen the depth of the shallow three‐dimensional seismic exploration is less than 100 m, one often encounters very low velocities for the target and high frequencies in the data. Following Nyquist–Shannon sampling theorem, the permissible maximum receiver interval can be smaller in this case compared to relatively deeper seismic exploration. This suggests that there are still issues to be addressed in the design of geometry and in data processing in shallow three‐dimensional seismic exploration. This paper addresses these problems by applying the theory of compressed sensing for signal processing to shallow‐seismic geometry designing and data processing. Theoretical research shows that random sampling of data can better reconstruct the wavefield than undersampled data. Random sampled data can transform the coherent aliasing to non‐coherent noise, which turns the seismic data interpretation problem into a data denoising problem. The jittered random sampling method avoids the situation when the spatial data points of a randomly sampled dataset are too concentrated or too sparse. Our proposed approach was tested on simulated and real seismic data. The results show that if the jittered random undersampling method is used in shallow three‐dimensional seismic data acquisition, then a wider range of observation with fewer receivers in the layout is possible. This greatly improves the data collection efficiency in the field. In addition, the random sampling method has more flexibility in the field environment. When using the regular sampling method, an open survey area without large obstacles is needed. However, the random sampling method can be adapted to rugged terrains. When obstacles are encountered, the receiver spacing can be increased appropriately. In open areas, the receiver spacing can be decreased to compensate for the reduced data.

SOUTH NATUNA BASIN RECONFIGURATION BASED ON RECENT SEISMIC AND GRAVITY SURVEYS

The Geological Survey Center has conducted a seismic survey in the southern Natuna Sea region to obtain geological information below relating to the potential energy resources of the area. The area research is located in the western part and outside the Singkawang Basin area (BG, 2008), which is separated by a Metamorf ridge. 2D seismic survey results show 3 different rock units, namely shallow marine sedimentary rocks, tertiary sedimentary rocks and pre-Tertiary sedimentary rocks, with pre-Tertiary sediment depths of less than 2000 ms. Interpretation of seismic data shows the pattern of graben structures that form sub-basins. strong refl ectors seen in seismic record can distinguish pre-rift, syn-rift and post-rift deposits. There are 2 wells, namely Datuk 1X and Ambu 1X. Datuk 1X has a depth of 1187 meters, and The Ambu 1X has a depth of 880 meters that is crossed by a seismic line. Both drilling has obtained Tertiary aged sandstone that covers pre-Tertiary bedrock.Gravity anomaly data in the seismic region shows anomaly values between 10 to 54 mgal which form the anomaly ridge and basinThe ridge anomaly extends as an anticline, while the anomaly basin also rises to form a syncline. Sincline and anticline trending southwest - southeast, with widening and narrowing patterns.Based on its geological model, the depth of the sediment is relatively shallow between 1500 to 2000 meters. While the integration between seismic, gravity and geomagnetic data shows the discovery of new basins that have never been described before.Finally, the integration of seismic and gravity data succeed discovers a new basin which has never been delineated before. In addition, it shows the continuity of the regional geological structure spanning from the studied area to the West Natuna Basin which is well known to be rich in hydrocarbon potential.

Attribute selection in seismic facies classification: Application to a Gulf of Mexico 3D seismic survey and the Barnett Shale

Automated seismic facies classification using machine-learning algorithms is becoming more common in the geophysics industry. Seismic attributes are frequently used as input because they may express geologic patterns or depositional environments better than the original seismic amplitude. Selecting appropriate attributes becomes a crucial part of the seismic facies classification analysis. For unsupervised learning, principal component analysis can reduce the dimensions of the data while maintaining the highest variance possible. For supervised learning, the best attribute subset can be built by selecting input attributes that are relevant to the output class and avoiding using redundant attributes that are similar to each other. Multiple attributes are tested to classify salt diapirs, mass transport deposits (MTDs), and the conformal reflector “background” for a 3D seismic marine survey acquired on the northern Gulf of Mexico shelf. We have analyzed attribute-to-attribute correlation and the correlation between the input attributes to the output classes to understand which attributes are relevant and which attributes are redundant. We found that amplitude and texture attribute families are able to differentiate salt, MTDs, and conformal reflectors. Our attribute selection workflow is also applied to the Barnett Shale play to differentiate limestone and shale facies. Multivariate analysis using filter, wrapper, and embedded algorithms was used to rank attributes by importance, so then the best attribute subset for classification is chosen. We find that attribute selection algorithms for supervised learning not only reduce computational cost but also enhance the performance of the classification.

Using machine learning as an aid to seismic geomorphology, which attributes are the best input?

Volcanic rocks with intermediate magma composition indicate distinctive patterns in seismic amplitude data. Depending on the processes by which they were extruded to the surface, these patterns may be chaotic, moderate-amplitude reflectors (indicative of pyroclastic flows) or continuous high-amplitude reflectors (indicative of lava flows). We have identified appropriate seismic attributes that highlight the characteristics of such patterns and use them as input to self-organizing maps to isolate these volcanic facies from their clastic counterpart. Our analysis indicates that such clustering is possible when the patterns are approximately self-similar, such that the appearance of objects does not change at different scales of observation. We adopt a workflow that can help interpreters to decide what methods and what attributes to use as an input for machine learning algorithms, depending on the nature of the target pattern of interest, and we apply it to the Kora 3D seismic survey acquired offshore in the Taranaki Basin, New Zealand. The resulting clusters are then interpreted using the limited well control and principles of seismic geomorphology.

Full-volume 3D seismic interpretation methods: A new step towards high-resolution seismic stratigraphy

Following decades of technological innovation, geologists now have access to extensive 3D seismic surveys across sedimentary basins. Using these voluminous data sets to better understand subsurface complexity relies on developing seismic stratigraphic workflows that allow very high-resolution interpretation within a cost-effective timeframe. We have developed an innovative 3D seismic interpretation workflow that combines full-volume and semi-automated horizon tracking with high-resolution 3D seismic stratigraphic analysis. The workflow consists of converting data from seismic (two-way traveltime) to a relative geological time (RGT) volume, in which a relative geological age is assigned to each point of the volume. The generation of a horizon stack is used to extract an unlimited number of chronostratigraphic surfaces (i.e., seismic horizons). Integrated stratigraphic tools may be used to navigate throughout the 3D seismic data to pick seismic unconformities using standard seismic stratigraphic principles in combination with geometric attributes. Here, we applied this workflow to a high-quality 3D seismic data set located in the Northern Carnarvon Basin (North West Shelf, Australia) and provided an example of high-resolution seismic stratigraphic interpretation from an Early Cretaceous shelf-margin system (Lower Barrow Group). This approach is used to identify 73 seismic sequences (i.e., clinothems) bounded by 74 seismic unconformities. Each clinothem presents an average duration of approximately 63,000 years (fifth stratigraphic order), which represents an unprecedented scale of observation for a Cretaceous depositional system on seismic data. This level of interpretation has a variety of applications, including high-resolution paleogeographical reconstructions and quantitative analysis of subsurface data. This innovative workflow constitutes a new step in seismic stratigraphy because it enables interpreters to map seismic sequences in a true 3D environment by taking into account the full variability of depositional systems at high frequency through time and space.

Pitfalls and implementation of data conditioning, attribute analysis, and self-organizing maps to 2D data: Application to the Exmouth Plateau, North Carnarvon Basin, Australia

Recent developments in attribute analysis and machine learning have significantly enhanced interpretation workflows of 3D seismic surveys. Nevertheless, even in 2018, many sedimentary basins are only covered by grids of 2D seismic lines. These 2D surveys are suitable for regional feature mapping and often identify targets in areas not covered by 3D surveys. With continuing pressure to cut costs in the hydrocarbon industry, it is crucial to extract as much information as possible from these 2D surveys. Unfortunately, much if not most modern interpretation software packages are designed to work exclusively with 3D data. To determine if we can apply 3D volumetric interpretation workflows to grids of 2D seismic lines, we have applied data conditioning, attribute analysis, and a machine-learning technique called self-organizing maps to the 2D data acquired over the Exmouth Plateau, North Carnarvon Basin, Australia. We find that these workflows allow us to significantly improve image quality, interpret regional geologic features, identify local anomalies, and perform seismic facies analysis. However, these workflows are not without pitfalls. We need to be careful in choosing the order of filters in the data conditioning workflow and be aware of reflector misties at line intersections. Vector data, such as reflector convergence, need to be extracted and then mapped component-by-component before combining the results. We are also unable to perform attribute extraction along a surface or geobody extraction for 2D data in our commercial interpretation software package. To address this issue, we devise a point-by-point attribute extraction workaround to overcome the incompatibility between 3D interpretation workflow and 2D data.

Can high-resolution reprocessed data replace the traditional 2D high-resolution seismic data acquired for site surveys?

Can high-resolution reprocessed data replace the traditional 2D high-resolution seismic data acquired for site surveys?

3D seismic datasets applied to mineral exploration: revisiting three Canadian case studies

The benefits of working with legacy seismic data are broad and valued in a wide range of geoscience applications and result from the comprehensive volume of industry and public seismic data acquired over several decades. Legacy seismic data exist in many parts of the world including areas that, due to stricter regulatory processes, environmental restrictions, demographic changes, or other factors would be challenging or even impossible to survey today. Examples are numerous but one includes 2D marine seismic data acquired in the 1980s with a large airgun array to provide a deep cross-section through the Appalachians beneath the now sen-sitive Gulf of St Lawrence, eastern Canada (Marillier et al., 1989). Sometimes benefits arise through the use of newly developed tech-niques to extract additional information from legacy seismic data. This idea is obviously not new and many examples can be found in the literature. One example is the use of extended Vibroseis cor-relation developed in 1980s (Okaya and Jarchow, 1989) applied to increase the depth range of marine Vibroseis seismic data acquired in 1971 in two of the Great Lakes of North America (Milkereit et al., 1992). Marine seismic data in the Great Lakes are sparse, but contain information about deep Grenvillian terranes that, in this case, could only be revealed using a technology developed more than a decade after data acquisition. Reflection seismology has been used for mineral exploration for more than 30 years (Reed, 1993). During that period, many case studies demonstrated the utility of the method for imaging deep lithological contacts and structures indirectly associated with mineralization, and for the direct imaging of deposits. Malehmir et al. (2012) provide a comprehensive overview of key accomplishments for various commodities and mining locations in Canada and around the world. In particular, many examples demonstrate the advantages of the 3D seismic method for providing high-resolution images of subsurface structures and deep-seated ore deposits in a variety of geological environ-ments. Several of these legacy 3D seismic data sets have been reprocessed with advanced and novel techniques to provide more reliable and detailed images of the subsurface. Here, we show three early examples of the application of 3D seismic data for mineral exploration in the Bathurst, Sudbury, and Val d’Or mining camps, Canada (Figure 1). Specifically, we demonstrate that reprocessing of 3D datasets from earlier applications of seismic reflection can refine the imaging of known ore deposits and can lead to the identification of new exploration targets. For the case studies presented here, most improvements resulted from processing and imaging strategies built from an understanding of the response of mineralized bodies on seismic data and improving specific steps that prevented their proper imaging on final volumes. The case studies are introduced according to their year of acquisition, starting from the oldest (i.e., the Trill 3D survey in the Sudbury mining camp) to the most recent (e.g., the Louvicourt 3D survey in the Val d’Or mining camp). All 3D seismic surveys are located in areas with limited access and difficult terrain and as a result, were acquired with explosives. Surface conditions varied for each survey area but included steep hills, extensive swamps, and thick glacial sediments. Geology also varied at the three sites. Host rocks are either nearly-transparent-to-seismic waves or are highly heterogeneous and generating seismic scattering potentially masking the response of the mineralized body. In all three areas, however, mineralized bodies scattered or reflected energy in a preferred direction, and were observed only on a limited number of prestack seismic traces. In some cases, such a sparse signature was buried in noise when stacking all traces and required particu-lar attention to be properly imaged.

Evolution of Low-Angle Normal Faults in the Enping Sag, the Northern South China Sea: Lateral Growth and Vertical Rotation

Low-angle normal faults (dip <30°, LANFs) are widespread in the northern margin of the South China Sea where the maximum crust thickness is approximately 30.0 km. Based on 3D seismic survey data and drilling wells in the Enping sag, evidences for LANFs that initially formed at high-angles are discussed. After a detailed investigation of extensional fault system and description of 3D fault geometry, the initial fault dips under the model of distributed vertical simple shear are also calculated. The results indicate that the present-day dip angles of the LANFs are in the range of 12° to 29°, and the initial fault dip angles are in the range of 39° to 49°. Deep seismic imaging suggests that the upper crust in the footwall block of the LANFs was tilted at an angle of ~14° to 22° due to the isostatic rebound during rifting. Moreover, the temporal and spatial sequences of the lateral growth of the LANFs have been investigated by the seismic interpretation of four isochronous stratigraphic interfaces, which demonstrates that two individual fault segments propagated towards each other and subsequently, were hard-linked during the Early Eocene.

Marine 3D seismic volumes from 2D seismic survey with large streamer feathering

Strong ocean current influences a marine seismic survey and forces the streamer off-course from the survey line. The sideway drift of the streamer results in that the reflection data are no longer distributed in common midpoint gathers along the survey line but become swath distribution on one side of the ship track. This effect is known as “streamer feathering” which degrades the profile image of the 2D processed seismic data. However, if we have long streamer or closely spaced parallel 2D seismic survey lines, we may turn this deleterious effect into a good opportunity to generate 3D seismic volumes with swath distributed reflection data. We present two case studies in which 2D seismic data were collected offshore eastern Taiwan where the strong Kuroshio Current heavily influenced the ship speed and caused large streamer feathering. The first case is a large-offset 2D seismic profiling data collected using a 6-km long streamer. We processed the swath part of the reflection data in 3D that not only avoids the inappropriate smearing effect in 2D data processing but also generates a 3D seismic volume to help the seismic interpretation. In the second case, we adjusted our 2D survey strategy when realizing that strong Kuroshio Current was causing significant streamer feathering, and collected a set of closely spaced parallel 2D seismic lines. This multi-swath dataset covers a broad area which enables us to generate a 3D seismic volume. Since our datasets are not real 3D seismic data, we have tailored our processing flows to deal with different data configurations and limitations of each dataset. Our results show that not only we have enhanced 2D seismic images of the originally-interested survey lines, but also provide information on 3D geometry of the geological features imaged. The benefits and limitations of utilizing the streamer feathering effect to generate 3D seismic volumes from 2D seismic profile data are reported. Overall, this approach is a considerable way to handle 2D seismic data with large streamer feathering for both avoiding unreliable 2D seismic images and obtaining information on 3D geometry of the geological features imaged.

Relocation of Seismic Events and Validation of Moment Tensor Inversion for SENTINELS Local Seismic Network

Seismic activity of Podhale (Poland) and Spiš (Slovakia) regions has been recognized for years. The first information about tremors from this area comes from the XVIII century. Four earthquakes, with intensity over VI in the MSK scale, were reported in 1643, 1724, 1840 and 1901. Since 1960’s an instrumental measurements have been conducted. However, until 2011 no stronger tremors have been recorded in the area of artificial water reservoir Czorsztyn lake located in extremely complex geotechnical condition, between border zone of Inner and Outer Carpathians separated by Pieniny Klippen Belt. Before Czorsztyn 2D seismic survey, knowledge of tectonic boundaries and velocities was very limited. The seismic survey confirmed assumptions of a flower type faults system and provided the first 3D velocity model for this area. After a series of earthquakes, in 2013 a SENTINELS network started its operation and since that time it recorded almost 200 events. The focal mechanisms were calculated for around 20 of them. Both location and moment tensor are crucial in the investigation of the origins of seismogenic process related to industrial operations. Therefore the relocation of the events and validation of the moment tensor solutions for the SENTINELS network were conducted with the use of a 3D velocity model. The validation of mechanisms was conducted with the use of the synthetic tests based on the 1D velocity model derived from the 3D velocity model, taking into account its lateral velocity anisotropy. It was based on the synthetic amplitudes generated with the assumed normal and strike-slip faulting type, similar to the obtained solutions. The validation proved that focal mechanisms are reliable even in a sparse focal coverage and noise not exceeding 40% of the P-wave amplitude. Most of the events are normal or strike-slip with nodal planes striking NW–SE or NNE-SSW. The latter ones are in agreement with the orientation of the main discontinuities in this area.

Cooperative inversion of magnetotelluric and seismic data on Shurab diapirs in Central Iran

Using diapirs as liquid or gas storage structures has increased because salt formations are considered to be extremely impermeable and non-reactive. The process of delineating the diapirs’ structures ends in lots of challenges due to their geological complexity. Therefore, the integration of different geophysical methods seems to be necessary to cover different physical characteristics of the diapirs. Shurab diapirs located at the NW of Kashan in Qom basin of Central Iran have been considered as candidates for the first natural gas storages in Iran. A previous 2D seismic survey across the diapir No. 4 of Shurab could not resolve the diapir structure properly and some ambiguities left unresolved. The main goal of this paper is to resolve the structure of diapir No. 4 by employing a cooperative inversion of the seismic and magnetotelluric (MT) data and a comparison with the joint inversion of transverse electric (TE) and transverse magnetic (TM) modes of the MT data. Both inversion schemes show the salt and sedimentary sequences of the stratigraphy of the Qom basin. The sequences of formations from the surface to depth are classified as upper red formation (URF), Qom formation (QF) and lower red formation (LRF). The results also show that the salt body has originated from the LRF. It is worthwhile to mention that the results from the cooperative inversion provide more details especially on the flanks and overhangs of the diapir No. 4. In addition, we have come to the conclusion that the right lateral strike-slip fault system is the most responsible phenomenon for the development of the diapirs in the survey area and the Sen–Sen fault plays a basic role as an elevator to pushing the salt up. The results are in good agreements with the resistivity and density logs of the boreholes. Moreover, the information from the geology, the cooperative inversion results on diapir No. 4, and the coincidence of the path of the Sen–Sen fault with the outcrops of the diapirs No. 1, 3 and 4 obviously provide that the tectonic scenario of the existence for diapir No. 4 could be appointed to the diapirs No. 1 and 3 equally. Another probable consequence would be the under surface continuation of the salt bodies all along the Sen–Sen fault, the verification of which requires regional MT surveys in a regular grid.

3D Seismic survey design using mixed‐radix based algorithm inversion

ABSTRACTThe determination of three‐dimensional geometry and acquisition parameters, the seismic acquisition survey design, is constantly subject of studies in obtaining data with the highest seismic quality, operational efficiency and cost minimization. In this paper, we propose a methodology for inverting geometry parameters of three‐dimensional orthogonal land seismic surveys based on a direct search method using a mixed‐radix based algorithm. In this algorithm, the search space is discretized on a mixed‐radix base, which depends on the extreme values and the search resolution of each parameter. We will show how to reparametrize the orthogonal acquisition geometry elements in order to obtain the independents and integers parameters that are necessary to construct the mixed‐radix base. For the optimization purpose, we define an objective function to contemplate target parameters associated with the elements of the acquisition geometry directly related to the geophysical and operational constraints. Taking in account that the mathematical functions and the objective function we define for the problem have no significant computational cost, all model space parameters are fast and efficiently tested. We applied the algorithm, using as input data, provided by a one‐line roll orthogonal reference geometry, assuming a pair of geological objectives as shallow and deep targets. All selected models that meet both the proposed objectives and the constraints are organized by decreasing order of fitness so that with the mixed‐radix inversion algorithm we found not only the best model, but also a set of suitable models. Likewise, with the best set of geometries, it is possible to establish a direct comparison between them, analysing their adherence to the technical and operational requirements according to the availability and degree of detail of each one. We show the top 10 best results as a table, allowing a direct comparison between all aspects of these geometries, and we summarize the results showing graphically the fitness of all selected geometries and the inverted geometry elements for the 1000 best geometries. These graphical displays provide a direct way to understand how each model behaves as the fitness decreases. The algorithm is very flexible and its application can be extended to any environment and type of acquisition geometry, and in any phase study of an area be it regional, exploratory or development.

Sparse 3D Seismic Imaging in the Kylylahti Mine Area, Eastern Finland: Comparison of Time Versus Depth Approach

A 10.5 km2 3D seismic survey was acquired over the Kylylahti mine area (Outokumpu mineral district, eastern Finland) as a part of the COGITO-MIN (COst-effective Geophysical Imaging Techniques for supporting Ongoing MINeral exploration in Europe) project, which aimed at the development of cost-effective geophysical imaging methods for mineral exploration. The cost-effectiveness in our case was related to the fact that an active-source 3D seismic survey was accomplished by using the receiver spread originally designed for a 3D passive survey. The 3D array recorded Vibroseis and dynamite shots from an active-source 2D seismic survey, from a vertical seismic profiling experiment survey, as well as some additional “random” Vibroseis and dynamite shots made to complement the 3D source distribution. The resulting 3D survey was characterized by irregular shooting geometry and relatively large receiver intervals (50 m). Using this dataset, we evaluate the effectiveness of the standard time-imaging approach (post-stack and pre-stack time migration) compared to depth imaging (standard and specialized Kirchhoff pre-stack depth migration, KPreSDM). Standard time-domain processing and imaging failed to convincingly portray the first ~1500 m of the subsurface, which was the primary interest of the survey. With a standard KPreSDM, we managed to obtain a good image of the base of the Kylylahti formation bordering the extent of the mineralization-hosting Outokumpu assemblage rocks, but otherwise the image was very noisy in the shallower section. The specialized KPreSDM approach (i.e., coherency-based Fresnel volume migration) resulted in a much cleaner image of the shallow, steeply dipping events, as well as some additional deeper reflectors, possibly representing repetition of the contact between the Outokumpu assemblage and the surrounding Kalevian metasediments at depth.

Integrated interpretation of seismic and magnetotelluric data on Shurab diapirs in Qom basin, Central Iran

In recent decades, diapirs are frequently used for CO2 and natural gas storage due to their extremely impermeable and non-reactive characteristics. Among various approaches, we use an integrated interpretation approach to resolve the diapir no. 4 belonging to the Shurab diapirs (SD). The SD is a group of diapirs that have pierced to the surface of the Qom basin of Central Iran, which is a candidate for natural gas storages. The complex geology of the SD is the main cause that previous 2D seismic surveys across the diapir could not provide required information to propose any location for any exploration borehole. Consequentially, 28 magnetotelluric (MT) and 1 audio-magnetotelluric station were measured along a SW-NE profile. Dimensionality and strike analysis for all stations is done by the use of phase tensor analysis. We used the nonlinear conjugate gradient algorithm to invert the TE- and TM-modes data simultaneously in 2D. The resistivity model was compared with the interpreted results of the post-stack depth migration model using seismic attributes. In order to extract the determinative geological information from the low-quality seismic section, envelope, variance, sweetness and instantaneous frequencies attributes were used. The integrated interpretation of the seismic and MT data resolves a precise geometry of the salt body, location of the dense part of the diapir as well as the tectonics around the diapir. The integrated interpretation of seismic and MT data of diapir no. 4 resulted in an exploration drilling program.

Reflector dip estimates based on seismic waveform curvature/flexure analysis

Reliable estimation of the reflector dip serves as a fundamental and essential tool for subsurface structure interpretation from 3D seismic surveys. We have developed a new method for accurate dip estimation, which consists of two major components. First, the curvature/flexure concept is adapted from the traditional reflector geometry analysis to work for the seismic waveforms, denoted as the waveform curvature and waveform flexure, respectively. Physically, both of them are capable of measuring the most and least apparent variation of the local waveforms in a seismic profile, and thus the corresponding measuring orientations represent the normal and dipping directions of the seismic reflectors, respectively. Second, the complex seismic trace is incorporated into our workflow of waveform curvature/flexure analysis to enhance the accuracy of dip estimation in the presence of seismic noises, especially in the zones of weak reflection intensity, such as zero crossings. The added values of our method are verified through various applications, such as horizon tracking and fault detection, to two 3D seismic data sets, one from the Netherlands North Sea and the other from the Great South Basin in New Zealand that is rich of faults. The results not only demonstrate the good accuracy of the generated dip vectors in guiding the seeded horizon tracking, but they also hold great potential for assisting seismic interpretation in more ways, such as structural-oriented filtering and attribute analysis.