Salt Dome Structures Research Articles

Reconstruction of the Subsurface of Al-Hassa Oasis Using Gravity Geophysical Data

Al-Hassa city, located in Eastern Saudi Arabia, boasts the world’s largest oasis and the most expansive naturally irrigated lands. Historically, a total of 280 natural springs facilitated significant groundwater discharge and irrigation of agricultural land. Furthermore, the water in certain springs formerly had a high temperature. The spatial variability of the water quality was evident. At the same time, Al-Hassa Oasis is situated on the northeastern side of the Ghawar field, which is the largest conventional onshore oil field in the world in terms of both reserves and daily output (approximately 3.8 mmb/d). The aforementioned traits suggest an intricate subsurface that has not yet been publicly and thoroughly characterized. Due to the presence of significant cultural noise caused by agricultural and nearby industrial activities, a robust, easy-to-use, and accurate geophysical method (gravity) was used to cover an area of 350 km2, producing the 3D subsurface model of the study area. A total of 571 gravity stations were collected, covering the whole Al-Hassa Oasis and parts of the nearby semi-urban areas. The gravity data were corrected and processed, and a 3D inversion was applied. The resulting 3D geophysical subsurface modeling unveiled an intricate subterranean configuration and revealed lateral variations in density, indicating the presence of a potential salt dome structure, as well as fracture zones that serve as conduits or obstacles to the flow of the subsurface fluids. This comprehensive modeling approach offers valuable insights into the subsurface dynamics of the broader study area, enhancing our understanding of its qualitative tectonic and hydraulic features and their impacts on the area’s natural resources, such as groundwater and hydrocarbons.

Structural and tectonic features of the Transcarpathian trough according to gravity and magnetic data

Based on the analysis and interpretation of gravity and magnetic field anomalies, we studiedthe peculiarities of fault tectonics, structural-tectonic structure (including salt dome tectonics) of the Transcarpathian trough. We identified signs of the manifestation of deep faults and other large structural-tectonic elements in anomalies of gravity and magnetic fields. We then traced these structural-tectonic units by comparing the morphology, intensity, dimensions, and directions of the typical anomalous zones in the gravitational and magnetic fields with the tectonic structure of the region.
 We used digital maps of gravitational and magnetic fields; averaging transforms and relief-shadow images, we mapped local gravimagnetic anomalies. Analysis of the spatial structure of the original gravimagnetic fields and their transforms and structural-tectonic maps yielded a reflection of large tectonic elements of fault tectonics, anticlinal and salt dome structures in the gravimagnetic fields. Based on gravimagnetic data, the tectonic structure of the Transcarpathian trough was clarified, and the boundaries of tectonic zones and microplates were traced. The zone of the Transcarpathian deep fault is identified as a tectonic zone traced by a band of intense local positive anomalies of the gravity field along the Flysch Carpathians to the border of the Marmarosh massif. It is limited by high gradients from the southwest and northeast and is a reflection of the Pieniny and Marmarosh rock zones. The zone of the Transcarpathian deep fault is considered a suture zone of the Inner and Flysch Carpathians. In the structure of the anomalous gravity field of the Transcarpathian trough, a number of local anomalies associated with salt stocks, as well as individual anomalies, expected to be connected to salt-bearing deposits, werefound.
 We confirmed the effectiveness of gravimagnetic methods in the geological conditions of the Transcarpathian trough to detect anticlinal structures, basement protrusions, which create favorable conditions for oil and gas traps in sedimentary strata. Interpreting anomalous gravimagnetic fields in combination with geological and tectonic materials is an important condition for the integral process of studying the geological and tectonic structure of the Earth’s crust in the Transcarpathian region.

Assessment of hydromineral resources of the southern part of the Pre-Ural Foredeep on the example of spring waters for household use and balneotherapy

The results of the research devoted to the geochemistry of natural sources of springs on the territory of the Pre-Ural Artesian Basin are relevant, since the springs are understudied and are not classified according to their chemical composition and purpose. The southern area of the Pre-Ural Artesian Basin with salt-gypsum tectonics was studied. There are many springs with various chemical compositions there. The prevailing salinity level of spring waters varies from 197 to 941 mg/l, with total hardness of 1.33-5.5 mg-eq/l, and with good quality drinking water. The goal was achieved. The hydrogeological conditions and hydrogeochemical characteristics of the source waters were studied. Analogues of mineral waters of the group without “specific” components and properties of the Krainsky and Varninsky types with the salinity level from 1.2-3.36 g/dm3 are found by comparative analysis: sulfate, bicarbonate-sulfate, sulfate-bicarbonate calcium, magnesium-calcium waters. Springs with high salinity sodium chloride leaching waters with 124 g/dm3 for balneotherapy are associated with salt dome structures. A certificate on the exact possible therapeutic properties of spring mineral waters can be issued by the Institutes of Health Research Study after research.

Hydrogeochemical characteristics of fresh waters in the springs of salt dome territories of the Cis-Urals region

The article presents the results of a study on the geochemistry of fresh water from natural sources (springs) in the salt dome territories of the Pre-Ural Artesian Basin. Spring waters are understudied; they are not classified according to their chemical composition and purpose. The research area is the territory of the Pre-Ural Artesian Basin in Orenburg Region with salt-gypsum tectonics. There are numerous springs with fresh water suitable for household and drinking purposes there. Springs with mineralization from 156 to 806 mg/dm3 of mixed composition, sulfate-chloride, sulfate-bicarbonate, bicarbonate and calcium and magnesium-calcium, sodium-magnesium-calcium are related to gypsum fields and salt dome structures. The total hardness varies from 3.5 to 10.27 mg/eq/l from moderately hard to extremely hard. The conclusion on the quantitative and qualitative assessment of spring waters should be made by prospecting and exploration activities with experimental filtration activities and assessment of reserves.

FORMATION CONDITIONS OF THE PALEOGENE COALS IN THE SULA-UDAISKE DEPOSIT OF THE DNIEPER-DONETS COAL-BEARING AREA

We studied brown coals in the Sula-Udaiske deposit, located within the Dnieper-Donets coal-bearing area, in the vast Sukhonosivsko-Romodanivsky compensation trough, which was formed as a result of the growth of the Logovikivska, Poznyakivska, Vysachkivska, Romodanivska, Hasenkivska salt-dome structures. The trough is filled with Paleogene- Neogene and Quaternary sediments. The Beretska formation of Paleogene is coal-bearing. It contains five coal seams, of which the most regular seams of working height are the Lower, which lies at the base of the coal-bearing strata, and the Upper, which completes the section. The brown coal deposit is confined to the deepest part of the trough and wedges out to its periphery. It is shown that the Paleogene brown coal formation is a multifacial structure that constitutes a cycle of sedimentation, one of the facies of which is coal. The composition of the sedimentation cycle was determined by the geotectonic regime, which defined the paleogeographic conditions, the rate of subsidence of the wetland, the degree of watering and flow of peatlands, and the scale of microbial activity. According to the groups of microcomponents quantitative ratio, brown coal is divided into petrographic types alternating in the section of the seam due to the cyclical change in the conditions of peat accumulation. Peat cyclicity is determined by different ratios in separate interlayers of different types of peat-forming plants, by heterogeneity of their remains and unequal degree of preservation of plant material. The predominant types of coal are gelites, lipoid-gelites and lipoid-gelitites, which make up 85% of the coal mine. In terms of quality indicators, the studied coals correspond to brown coals of a low coalification degree. It was found that the peat accumulation during the formation of working height layers occurred in the coastal sea lowland conditions, as well as in the conditions of overgrown lakes and flooded forest swamp.

Assessing model uncertainty for the scaling function inversion of potential fields

We have used the very fast simulated annealing algorithm to invert the scaling function along selected ridges, lying in a vertical section formed by upward continuing gravity data to a set of altitudes. The scaling function is formed by the ratio of the field derivative by the field itself, and it is evaluated along the lines formed by the zeros of the horizontal field derivative at a set of altitudes. We also use the same algorithm to invert gravity anomalies only at the measurement altitude. Our goal is to analyze the different models obtained through the two different inversions and to evaluate the relative uncertainties. One main difference is that the scaling function inversion is independent of density and the unknowns are the geometric parameters of the source. The gravity data are instead inverted for the source geometry and the density simultaneously. A priori information used for both the inversions is that the source has a known depth to the top. We examine the results over the synthetic examples of a salt dome structure generated by Talwani’s approach and real gravity data sets over the Mors salt dome (Denmark) and the Decorah Basin (USA). For all of these cases, the scaling function inversion yields models with better sensitivity to specific features of the sources, such as the tilt of the body, and reduced uncertainty. Finally, we analyze the density, which is one of the unknowns for the gravity inversion, and it is estimated from the geometric model for the scaling function inversion. The histograms over the density estimated at many iterations indicate a very concentrated distribution for the scaling function, whereas the density contrast retrieved by the gravity inversion, according to the fundamental ambiguity density/volume, is widely dispersed, making it difficult to assess its best estimate.

Geochemistry of evaporitic deposits from the Cenomanian (Upper Cretaceous) Maha Sarakham Formation in the Khorat Basin, northeastern Thailand

The Cenomanian (Upper Cretaceous) Maha Sarakham Formation of the Khorat Basin, northeastern Thailand consists of three evaporite units (Lower, Middle and Upper Salt) interbedded with clastic sediments and exhibits abundant deposits of potash. Although numerous studies have been carried out on the Khorat potash deposit, results are still equivocal with regard to the origin of the rock salt, whether it was marine or non-marine (hydrothermal and/or mixed fluids). The purpose of this study is to examine the origin of rock salt based on elemental compositions and boron isotope analyses in the southwestern part of the Khorat Basin. A stratigraphic correlation of five boreholes (K-201– 205) located in Bamnet Narong and Chaturat districts, Chaiyaphum province, Thailand, revealed a salt dome structure. The elemental composition and δ11B values in the longest borehole K-203 indicate a precipitation of halite and carnallite from seawater. Rare earth elements (REE) of claystone and siltstone from five boreholes (K-201– 205) are comparable to the REE of sandstone from the Simao Basin in China, which suggest a similar provenance. Stratigraphic comparisons and geochemical signatures are important for a better understanding of the recharge models of paleoseawater. In agreement with some previous studies, we conclude that the Cenomanian evaporites within the Khorat Basin are marine deposits.

Underground waters of salt-dome basins: a case study of the Caspian depression and its nothern surroundings (Volga-Ural Anteclise and Pre-ural foredeep)

The area under study is located in the place where the Caspian Depression joins the Pre-Ural Foredeep and the Volga-Ural Anteclise and where the salt-dome and salt-gypsum tectonics is manifested. The development of salt-gypsum tectonics is a specific feature of the Pre-Ural Foredeep from the viewpoint of tectonics. The modern relief of the Caspian Depression was developed in the Quaternary Period. Its development was accompanied by repeated transgressions of the sea. There are many springs with potable water that are suitable for drinking in the northern part of the Caspian Depression and in the southern part of the Volga-Ural Anteclise and the Pre-Ural Foredeep. There are springs with mineral water and springs that can be used for balneotherapy. Springs with potable water of good quality with mineralization 0.3-0.7 g/dm are revealed in the zone of active water exchange3. Sulphate, sulphate-chloride groups of mineral waters without “specific” components and properties with mineralization 1.7-2.7 g/dm are revealed in the zone of slow water exchange 1.7-2.7 g/dm3. The class of sulphate-chloride waters is widely represented in the territory under study, there are mineral waters drained by springs with mineralization 1.9-4.9 g/dm3. The springs are close analogues of Krainka, Kazanian, Kashin, Khilovo and Chartak types of mineral potable waters. Springs with chloride sodium waters of leaching zones that can be used for balneotherapy with mineralization from 14.5 to 192.3 g/dm3 are linked to salt dome structures. Elton salt-dome structure of the western Caspian Depression is rich in hydromineral resources-mineral springs, rivers, brine of the lake Elton with bromine and sulphurous waters.

ROMNY SALT DOME STRUCTURE (DNIPRO-DONETS BASIN): GEOLOGICAL HISTORY AND HYDROCARBON POTENTIAL

The geological structure of the Romny salt dome and related the Romny oil field as the first discovered one in the Eastern region of Ukraine are described. The history of its discovery and development of the field are featured. The geological and geophysical study of this area is characterized. Under generalization of geological and geophysical data, paleotectonic and peleogeothermal reconstructions on the Romny structure derived from the results of drilling of Gerasymivska-1 exploration well. The cyclic intermittent development of the salt dome structure is demonstrated. It is proved that the upper intersalt Frasnian source rocks could generate hydrocarbons starting from the early Visean time. According to the results of seismic surveys the uplifted block is outlined in the area of the northern edge of the salt dome. The presence of hydrocarbon pools in of the Visean and Serpukhovian granular reservoirs as well as in the salt breccia is predicted applying seismic attributes analysis for this block. The carbonate reservoirs of the lower part of the Bashkirian sequence, the productivity of which is established at the nearest located Velyki Bubny field, can be potentially oil and gas-bearing.

Post-salt trapping mechanism of south-east Pre-Caspian and its application to petroleum exploration

The Kungurian saliferous sediments of the Pre-Caspian sedimentary basin represented by thick stratum of rock salt with interlayered lenses of anhydrites, terrigenous and carbonate rocks. Initial thickness of these sediments estimated as 4000–4500 m at the center of the depression and 1000–2000 m on the edges of the basin. The processes of halokinesis led to formation of more than 1200 salt dome structures represented by salt diapirs and walls, ridges and salt pillows. Number of salt dome related structures of Mesozoic clastic deposits revealed by seismic exploration carried out in 70–90′s of last century are quite common on the south-eastern part of the Pre-Caspian Sedimentary basin. Most of hydrocarbon pools in post-salt clastic rocks have been discovered on fault-related anticline prospects which are derived from salt tectonics morphologically variable (Munyithya et al. Petrol Explor Prod Technol 10: 2257–2267. https://doi.org/10.1007/s13202-020-00917-1, 2020). Other potential traps anticipated in the area are stratigraphic traps, pinch-out and unconformity-related traps, trapped by salt domes and walls or by salt overhang, etc.

REGULARITIES OF NATURAL AND ANTROPOGENIC HAZARDOUS PROCESSES DEVELOPMENT FOR SOLOTVYNO (TRANSCARPATHIA, UKRAINE)

The consequences of the rock-salt resources usage in Solotvyno, the causes of technogenic environmental emergency situation, activity of governmental structures and the participation of international experts to overcome it are considered. The developed zoning scheme of hazardous geological processes and their consequences are represented. This scheme, constructed in the ESRI software, have been provided basing on expert assessment: former hazardous events frequency and scale, changing of topography and geomorphology, geodetic survey, remote sensing data (satellite imagery, Differential Interferometric Analysis data), authors systematic field observations, coupled with summarized previous research results and monitoring studies of terrain altitude in various years, by different methods and a number of research teams. Zones cover territories ranked by the probability of subsidence, sinkholes formation (ground surface collapses), landslides, karst, suffosion, erosion, floods, flooding, increased mineralization of aquifers used for water supply, etc. The presented scheme is proposed as the basis for ensuring life safety in Solotvyno during the territory development and monitoring system establishment, and then based on the monitoring results obtained, the scheme will be improved, detalized and acquire a predictive focus. Therefore because of the complicated geoecological situation, development and functioning of a permanent geoecological monitoring system for the Solotvyno salt dome structure and adjacent territories is a priority objective.

GEOLOGICAL AND GEOPHYSICAL CHARACTERISTICS OF THE ANABAR‐KHATANGA OIL AND GAS PROVINCE; NUMERICAL MODELING OF THE PROCESSES OF FORMATION OF SALT DOMES (SIBERIAN SECTOR OF THE RUSSIAN ARCTICS)

The article discusses the geological structure, oil‐and‐gas‐bearing capacities and salt tectogenesis of the Anabar‐Khatanga saddle located on the Laptev Sea shore. In the study area, the platform sediments are represented by the 14‐45 km thick Neoproterozoic‐Mesozoic sedimentary complexes. The regional cross‐sections show the early and middle Devonian salt‐bearing strata and associated salt domes in the sedimentary cover, which may be indicative of potential hydrocarbon‐containing structures. Diapirs reaching the ground surface can be associated with structures capable of trapping hydrocarbons, and typical anticline structures can occur above the domes buried beneath the sediments. In our study, we used the algorithms and software packages developed by A.A. Trofimuk Institute of Petroleum Geology and Geophysics (IPGG SB RAS). Taking into account the structural geological features of the study area, we conducted numerical simulation of the formation of salt dome structures. According to the numerical models, contrasting domes that reached the ground surface began to form in the early Permian and developed most intensely in the Mesozoic, and the buried diapirs developed mainly in the late Cretaceous and Cenozoic.

DYNAMICS OF THE DEVELOPMENT SALT-DOME STRUCTURES OF THE CENTRAL PART OF THE DNIEPER-DONETS DEPRESSION

The Dniprо-Donets Depression is the main oil and gas region of Ukraine. The region is characterized by a wide distribution of salt dome structures that are objects of oil and gas exploration. The complex and long history of the region’s formation caused the creation of the structural-tectonic zonation of the Dniprо-Donets Depression, which includes: the northern and southern marginal (near-edge) zones (or seam zones of the Pripyatsky-Manitsky and Baranovitsko- Astrakhansky deep faults), pre-axial (or zones of near-ridge basement protrusions) and axial zones. The southern and northern marginal (edge) zones are the immersed slopes of the Ukrainian Shield and the Voronezh Crystalline Massif. Riftogenesis and halokinesis were the factors that have influenced the cyclical course of the evolution of salt domes, for which the asynchronous level of development was characteristic in certain geological epochs, due to their confinement to different structural and tectonic zones of the depression. The morphological features of salt structures, the distribution and nature of disjunctive dislocations, stratigraphic and lithological gaps and unconformities are reflected in the distribution of oil and gas traps. In developed oil and gas regions, where tasks of geological exploration works become more complicated, the value of paleotectonic researches for forecasting traps and their oil and gas content is substantially increased. The main stages of the formation of salt structures located in the axial, southern and northern marginal structural and tectonic zones of the depression on the graphs of sedimentation rates are considered. When comparing charts of sedimentation rates according to the wells data, in the Tournaisian through the early Permian interval there is a synchronous (according to the epochs) jump-like character of the development of structures, regardless of their location within structural and tectonic zones is observed. The general slowdown of sedimentation rates from the Paleozoic to the Mesozoic, from the Mesozoic to the Cenozoic era, is characteristic for the whole territory of the Dnipro-Donets Depression. For the Kreminkivskaya-402 borehole maximum values correspond to the Middle and Late Devonian and Bashkirian, middle values to the Late Visean, Serpukhovian, and the minimal values – to the Tournaisian and Early Visean time. For the Skorobagatkivska-2 borehole the maximum values correspond to the Middle and Late Devonian, Late Visean, Bashkirian and Late Carboniferous, the middle values correspond to the Tournaisian- Early Visean and Moscovian, and the minimal values – to the Serpukhovian and Early Permian. For the Herasymivska-1 borehole the maximum values are characteristic for the Middle and Late Devonian, Late Visean and Bashkirian; the middle values – to the Tournaisian and Moscovian, and the minimal values – for the Late Visean and Serpukhovian.

The Gramian Method of Joint Inversion of the Gravity Gradiometry and Seismic Data

Integration of multimodal geophysical data provides better constraints on the results of inversion, thus helping to obtain the most reliable information about the structure and composition of the target. The Gramian method of joint inversion uses a Gramian stabilizer to increase the correlation between the different physical parameters of the inverse model and their attributes or transforms. This paper applies the Gramian method to a joint inversion of the gravity gradiometry and seismic data with rock physics and structural constraints. In the first case we construct the Gramian stabilizer, which enforces the petrophysical relationship between the physical parameters to constrain the recovered models. In the second case, we incorporate the structural constraints in the joint inversion via a Gramian stabilizer of the gradients of velocity and density. In this case, the Gramian forces the vectors of the gradients of different model parameters to be parallel, thus implementing the structural constraints. The Gramian method of joint inversion is implemented using the Tikhonov regularization and the re-weighted conjugate gradient method. The approach is illustrated by synthetic model studies, which include a complicated SEG model of a salt dome structure located in a complex environment.

VSP measurements used as a tool for improving seismic sub-salt imaging in brownfield development

Many of the Paleozoic Rotliegend low-permeability dry gas fields in the Southern Permian Basin of northern Germany are covered by Mesozoic salt dome structures. The resulting complexity in the overburden leads to imaging problems in subsalt reservoirs typically situated at depths between 4000 m to 5000 m TVD. Since structural compartmentalization is often the key challenge in field development, good resolution seismic is essential for well planning. For the study area, only a vintage 3D seismic survey from 1993/94 with limited data quality exists. Acquisition of new 3D seismic data is not possible owing to permitting restrictions and public resistance. Therefore the focus is on the acquisition of 2D VSPs in every new drilled well. The VSP measurements give local insights into the reservoir in the vicinity of the wellbore. With a general structural understanding and production history in mind, those local insights generate immense value for the understanding of the field.

A numerical approach for investigation of stress states induced by salt structures

The main oil and gas reserves around the world are found in regions containing evaporitic rocks. Owing to their low porosity and low permeability these rocks provide favorable conditions for hydrocarbon trapping, increasing the probability of success in oil and gas exploration. Salt rocks exhibit time-dependent strain behavior when submitted to deviatoric stresses. This behavior is described by creep constitutive laws based on deformation mechanics. One of the major challenges in modeling stress states in sedimentary basins in the presence of salt structures is to predict the magnitude of stress perturbations around salt bodies. This work presents a geo-mechanical approach to take into account the specific weight variation throughout the lithology and the effects of buoyancy in the resulting forces on the interface salt-body/formation. Modeling is driven by the fact that salt bodies cannot sustain deviatoric stresses. Numerical analyses using the Finite Element Method under plane strain conditions provide the results for the comparison of the methodologies found in the literature with the one proposed by the authors. Two synthetic models with salt dome structures are investigated. The proposed approach provided more realistic stress fields in the vicinity of salt structures.

Геологічна пам’ятка природи «Висачківський соляний купол»

The objective of this work is to describe the features of the geological structure of a unique natural site “Vysachkivsky pahorb” ( the Vysachkivsky dome ) and its recognition as a significant object of geological heritage. We analyzed the long history of accumulation of knowledge on the origin of the saline structure and the wide range of changes in the thinking of dome researchers regarding its origin, from the dyke theory to the salt-dome structure theory. The significant role of M.S. Shatsky was highlighted, who not only changed the state of thinking on the origin of the diapir structure, but also made first prognosis of prospects of the saline-dome structures of the Dnieper-Donets Rift for oil and gas extraction. This article critically considers the methods of interpretation of the formation of the Vysachkivsky dome as a result of post-Oligocene volcanism, describes the lithological-petrographic and mineralogical compound of the depository-volcanogenic formations according to the contemporary data and analyses its similarity and synchronism with vulcanites of the Mokra Volnovaha river basin. The article considers some theoretical approaches to the problem of saline diapirs in the Dnieper-Donetsk Rift, their structural-tectonic, formation and ancient origin, connection with halotectokinesis, presents the results of studying the Upper-Frasnian brachiopods in limestones of the Vysachkivsky saline dome`s cap rock, obtained by O. M.Kutsyba in 1936, which made it possible to date the salt to the Devonian era. The article considers the question of recognizing saline diapirism as one of the most favourable factors of deep thermal water discharge, and also as a channel of mantle exhalations penetrating into rocks of sedimentary cover due to their tendency to accumulate in deep-seated faults of the basement, and correspondingly as a channel for hydrocarbon and ore-bearing fluids to reach the upper structural levels. Work on inventory, cataloguing, and creating a data base on geological natural relics of Ukraine, conducted with the authors’ participation, has identified the place of the geological relic the Vysachkivsky saline dome in the nature-conservation fund of Ukraine, and established its significant historical, recreational, scientific and educational and scientific-practical value as a unique natural relic, worthy of protection at international level. Keywords: geological monument, Vysachki, diapirs, salt stock, diabase, basalt, DDD

Physical and mathematical modeling of transient electromagnetic soundings over salt-dome structures

This paper presents the results of physical and mathematical modeling performed to evaluate the potential of transient electromagnetic sounding in areas of salt-dome tectonics. Two geoelectric arrays are considered: an array with an inductive source (a horizontal loop) and an array with a mixed-type source (a horizontal current line). It is shown that the transient electromagnetic method provides important information on the relief of the top of salt deposits.

Understanding the seismic disorder attribute and its applications

While reflections associated with conformal sedimentary layers are usually coherent and continuous, other reflections, such as mass-transport complexes, karst collapse, and salt, may appear to be quite chaotic, without any specific orientation. We also may see chaotic events that have little to do with the target geology but rather are artifacts due to variations in the overburden and surface or budget limitations resulting in a suboptimum acquisition program. While some of these artifact issues can be handled at the time of processing, a certain level of randomness remains in most seismic data volumes. Geologic features of interpretational interest, such as fault damage zones, unconformities, and gas chimneys, often have randomness associated with them. The published work on randomness describes techniques such as cross correlation, which measures randomness associated with noise, the chaos attribute based on eigen-analysis of gradient covariance, and the seismic disorder attribute based on application of second derivative operators in the three axial directions in a 3D seismic volume. We apply the seismic disorder attribute to two different data sets and find that it is a useful attribute for assessing the signal-to-noise ratio and data quality, in addition to helping delineate damage zones associated with large faults and the interior of salt dome structures.

Salt-related structure geologic model of Pre-Caspian Basin and analysis on imaging capability

The Pre-Caspian Basin is one of the most prolific petroliferous basins in Kazakhstan. However, the hydrocarbon reservoir is always located in salt dome and pre-salt structures. The salt-related structure is so complex that it is difficult to obtain the satisfied imaging results. In order to improve the imaging precision and provide authentic amplitude information to reservoir prediction, we should analyze the imaging and amplitude preserving capability between different migration methods. According to actual geologic and reservoir characteristics, we design a typical complex salt-related structure model of the basin. Based on the forward modelling seismic record, we compare the one-way wave-equation pre-stack depth migration (WPDM) and pre-stack reverse-time depth migration (RTM). The results show that RTM can greatly improve the imaging quality of salt dome, but its improvement for the pre-salt structures is small compared with WPDM. Both methods are equally capable of preserving seismic reflection characteristics that affected mainly by the lateral variation of overlying strata.