The common depth point stack

In the Earth studies, discoveries and investigations of impact craters buried beneath thick sediments are sporadic so far and may still remain inefficient, unless geophysical surveys of the areas of interest are initiated. Such studies can provide useful data to develop the knowledge about cosmic events of the past geological eras, as well as contribute to industrial development of the areas. It is known that an impact crater is filled with layered deposits that create specific sequences and are generally thicker that deposits outside the crater. We have investigated a Precambrian crater located in the southern part of the Nepa-Botuoba anteclise of the Siberian platform. This impact crater called Nepsky-1 was discovered by seismic surveys using the common depth point method (CDPM). In our study, we used the geological and geophysical deep-drilling data of three wells, including gamma-ray and neutron logs and lithological core descriptions. With reference to the concepts of regional geological conditions, we reconstructed the conditions of sedimentation in the study area based on a comprehensive analysis of the structural and textural features of the rocks, and logging and seismic survey data. By processing and interpretation of the CDPM 3D seismic survey data, we obtained the structural images and cross-sections of the impact crater and analysed the thickness of its fill deposits. The Nepsky-1 crater is a bowl-shaped structure with a rim composed of allogenic breccia. In the area around the crater, fault systems are detected. Based on the core sample analysis, we identified the lithological members of the crater and its rim and described them in detail. Active compensation with lacustrine-delta sediments took place in the Nepa period of the late Vendian. By the end of the Tira time, the crater was completely leveled up. In our study, we obtained the first data on the structure of the crater section of the Vendian deposits. Sedimentation in the study area was controlled by the sea level changes. The main terrigenous productive horizons are confined to sandstones that accumulated during the sea level low stand, and found at the bottoms of the lower and upper Nepa subsuites, as well as at the bottoms of the lower and upper Tira subsuites. It is established that the study area was tectonically active in the late Tira time. As a result, the sediments filling the crater were removed to subaerial conditions, and the edges of the allogenic breccia rim were partially destroyed and formed granite breccia outgrowths observed in the rim’s cross-section. We conclude that in the Nepa and Tira times, tectonic vertical movements initiated relatively fast weathering and transportation of the terrigenous material from the adjacent hills into the sedimentation basin. The Nepsky-1 crater gives evidence of meteorite bombing of the Siberian paleocontinent in Precambrian. Finding similar crater structures can be reasonably expected in the study region. Considering the increased thicknesses of crater fill deposits, buried craters are promising potential for discovering oil-source and overlying seal rocks, which is important for petroleum industry.

Actuality. The hydrocarbon generation sources in the South Caspian Basin (SCB) are located at the depth of nine or more kilometers, where the organic-rich Maikop sediments occur. The main oil-and-gas fields here are found in reservoirs of the Productive Strata (Lower Pliocene), bedding at a depth of one or more kilometers. At the same time, the significant role at the process of hydrocarbons migration from the source of their generation to the reservoirs belongs to the tectonic faults (fractures). However, the results of the research according to the latest seismic data carried out in recent years are indicated the unavailability of the tectonic faults in the SCB, which connected the hydrocarbon generation sources with the reservoirs in the Productive Strata.
 Target. The determination of the geological elements at the studied area that contributed the role of the hydrocarbon migration channels and connected generation source with reservoirs in the Productive Strata.
 Objects. The hydrocarbon generation source, hydrocarbon migration channel, tectonic faults and fractures, Productive Strata reservoirs, eruptive channels of the mud volcanoes.
 Approach. The collaboration interpretation results of the deep drilling and the seismic data by using the common depth point method.
 Results. Based on the structural interpretation results of the seismic data with high-resolution parameters, are indicated the lack of the tectonic faults which connecting the hydrocarbon generation source with reservoirs of the Productive Strata in the SCB.
 In addition, the hydrocarbons that generated in the Maikop sediments are transported to the Productive Strata reservoirs by the eruptive channels of mud volcanoes. The opinion that the process of hydrocarbon generation in the Maikop clay deposits continues to the present time and the mud volcanoes eruptive channels provide feeding of the deposits with the continuous supply of oil-and-gas was expressed. Such kind of mechanism allows to classify the deposits, that more than a century under developed in the South Caspian Depression and which located at the zone of mud volcanomaturity, to the category of replenished.

The primary purpose of this paper is to show the benefits obtained from coordinating seismic and geologic information into an acceptable interpretation of the subsurface geologic conditions existing at a particular gas storage project. During 1974 and 1975, seismic explorations, utilizing the common depth point (CDP) technique and the Vibroseis energy method, were conducted at Northern Natural Gas Company's Dallas Center Aquifer Storage Prospect in central Iowa and Lyons Depleted Gas Field Storage Prospect in central Kansas. Although these two areas are geographically far removed from one another, the CDP technique is quite applicable to each of these geologic provinces. The petroleum engineer's need for detailed information about the configuration and integrity of the gas storage reservoir often surpasses the geologist's knowledge, based on a finite number of drill holes. The seismologist, working in close association with the geologist and utilizing modern field recording techniques, instruments and computer data enhancement, can add a new dimension to the understanding and thinking of both the petroleum engineer and geologist. Introduction The Dallas Center Anticline, located in Dallas County, Iowa, is 300 miles northeast of the Lyons Anticline, located in Rice County, Kansas. Both of these geologic structures have been evaluated by shallow and deep drill holes and by common depth point seismic work. The purpose of this evaluation was to prove their purpose of this evaluation was to prove their relative worth either as an aquifer gas storage prospect (Dallas Center) or to more accurately prospect (Dallas Center) or to more accurately define the boundary faults associated with an abandoned gas field (Lyons). Figure 1, an index map, shows the location of these two anticlines in relation to each other and to State and County boundaries, as well as major geologic features. Geologically, the two anticlines are in entirely different provinces. The Dallas Center Anticline is located at the extreme northern end of the Forest City Basin, eight miles east of the southeastern edge of the Mid-continent Gravity-Magnetic High. The Lyons Anticline is located on the southern half of the Genesco Uplift, the eastern most lobe of the larger Central Kansas Uplift. The Dallas Center Anticline was originally delineated by Northern Natural Gas Company from preliminary structural mapping of shallow farm preliminary structural mapping of shallow farm water well data.

The effectiveness of shallow high resolution ‘seismic reflection (i.e., resolution potential) to image geologic interfaces between about 70 and 750 ft at the Aberdeen Proving Grounds, Maryland (APG), appears to vary locally with the geometric complexity of the unconsolidated sediments that overlay crystalline bedrock. The bedrock surface (which represents the primary geologic target of this study) was imaged at each of three test areas on walkaway noise tests and CDP (common depth point) stacked data. Proven high resolution techniques were used to design and acquire data on this survey. Feasibility of the technique and minimum acquisition requirements were determined through evaluation and correlation of walkaway noise tests, CDP survey lines, and a downhole velocity check shot survey. Data processing and analysis revealed several critical attributes of shallow seismic data from APG that need careful consideration and compensation on reflection data sets. This survey determined: 1) the feasibility of the technique, 2) the resolution potential (both horizontal and vertical) of the technique, 3) the optimum source for this site, 4) the optimum acquisition geometries, 5) general processing flow, and 6) a basic idea of the acoustic variability across this site. Source testing involved an accelerated weight drop, land air gun, downhole black powder charge, sledge hammer/plate, and high frequency vibrator. Shallow seismic reflection profiles provided for a more detailed picture of the geometric complexity and variability of the distinct clay sequences (aquatards), previously inferred from drilling to be present, based on sparse drill holes and basewide conceptual models. The seismic data also reveal a clear explanation for the difficulties previously noted in correlating individual, borehole-identified sand or clay units over even short distances. Geologic cross-sections derived from CDP stacked data and borehole logs suggest locally complex geometries and horizontally variable geologic contacts.

Feasibility of detecting embedded cracks in concrete structures by reflection seismology

Seismic wave velocities, including effective velocities, play a critical role in the kinematic processing and interpretation of 2D and 3D seismic data. Along with other parameters of elastic waves, the geological efficiency of seismic exploration also depends on the level of knowledge of the velocity model of the medium, on the accuracy of information about velocities. The article briefly lists the main methods for determining the effective velocities according to the seismic wave field, developed and applied in the practice of seismic research. The methods used to determine the effective velocities of reflected waves can be divided into two groups: methods for determining the effective velocities based on automatic or visual tracking of the in-phase axes (i.e. hodographs) of reflected waves on seismic records, then their approximation by hyperbolas constitute the first group, and the second the group consists of methods based on the application of the analysis of the seismic wave field in controlled directions on the seismograms of a common depth point (CDP). Each proposed method for determining effective speeds has advantages and disadvantages. The article focuses on the industrial method, widely used at present, based on the analysis of the wave field in controlled directions, which do not provide sufficient information to solve the main problems of kinematic interpretation. The main disadvantages of the existing methods are indicated. The article describes a new method for determining the effective velocity, which is fundamentally different from the methods that are still used in the practice of seismic exploration. The fact is that in this method, seismic survey data of single and multiple profiling are not used separately, as it was in the methods used in seismic survey practice so far, but together. Formulas have been derived for determining the effective velocity based on the time gradients of the travel time curves of the CSP and CDP of reflected waves, which makes it possible to determine the speeds even from incomplete travel time curves. A technique for determining the effective speed has been developed and a sequence of procedures has been determined for solving the problem. The results of research are given on a specific example by solving the direct and inverse problems for the Sazhdag area between the Kura and Gabyrra rivers. The influence of errors in the values of the parameters included in the formula for calculating the effective speed on the final results is studied. At the end of the article, the main advantages of the proposed method are indicated.

The principal objective of seismic exploration is to determine three geologic parameters, the structural top, the bottom, and the lateral extent of an oil and gas reservoir. Conventional (100%) data is very efficient in locating the structural top and bottom of reservoirs. Two-dimensional (2D) common depth point (CDP) seismic data provides an immense improvement in seismic data quality over conventional (100%) data. This improvement enables the explorer to better visualize and map the reservoir in each direction of the seismic line. Three-dimensional (3D) seismic technology provides even more mappable data and capability. The explorer may visualize every imaginable direction and subtlety of a reservoir. This talk compares conventional (100%), two-dimensional (2D), and three-dimensional (3D) seismic data from the Midcontinent. Case histories of the Douglass (Upper Pennsylvanian) in Texas, the Morrow (Lower Pennsylvanian) in Colorado, the {open_quotes}Chat{close_quotes} (Mississippian) and the Hunton (Silurian-Devonian) in Oklahoma, and the Simpson (Ordovician) in Kansas will be discussed. Major and independent operators can maximize their exploration efforts by integrating existing data with three-dimensional (3D) technology and a solid geologic interpretation.

The basic requirements to recover plane layers of constant interval velocity, arbitrary dip and strike from common depth point (CDP) recordings are the following four quantities related to the primary event of each reflector at the common midpoint of a CDP profile: a) Two‐way normal time b) Normal moveout velocity within one arbitrary CDP profile c) Time slope of normally reflected rays within the profile d) Time slope of normally reflected rays in some other direction. The solution of the inverse problem is obtained directly. The moveout velocity is expressed in terms of seismic parameters along the normal incidence path in three dimensions and the direction of the profile within the free surface. A formula connecting dip and strike of the emerging normal ray with the measured time gradients is given and discussed. The method includes, as a special case, the Dix formulas for plane parallel layers.

Common depth point (CDP) recording, sometimes called common mid point (CMP), is a basic method in present day seismic exploration, whether that is the normal linear 2-D type or 3-D recording. However, to understand the concept fully, it is necessary to look back on the history of seismic exploration with respect, in the main, to the geometry of the recording spread and its effect on the processing and the interpretation of the recorded data. Some references to this topic have already been made, earlier in this book.

Prospects delineation and evaluation using the CDP gathers characterization, onshore Nile Delta, Egypt

Geological structures such as faults and fractures have an important influence in the process of fluid movement below the surface. The hydraulic behavior in aquifers can be determined by proper characterization of fractures, fault zones and their connectivity. In this study, we concern on detection and identification of fault zones in the groundwater basin to verify whether faults in the basin area connect to the surface, and whether the fault zones occurring serve as conduits or barriers for groundwater to flow. The seismic reflection method with Common Depth Point (CDP) profiling technique has been applied in this study. Through this study, we have identified that several large and small-scale faults were found in the study area. Generally, these large-scale faults cut the bedrock (granodiorite) up to impermeable layer. This large-scale fault group can be a barrier that block the groundwater flow. The fault zone is connected to the surface as evidenced by the presence of normal fault that is clearly observed at the surface. This seismic method is good to apply in this study because it can be used to record deeper subsurface conditions, especially for fault zone detection purposes.

Summary Water column variations are an important source of non-repeatability in time-lapse marine surveys. In a deep water context, the physical property variations within the water layers can generate significant time-shifts between repeated time-lapse seismic data. We present a new methodology for estimating water velocity changes and correcting the 4D seismic datasets. Each sail line is migrated independently and Common Depth Point (CDP) gathers are produced for the overburden along a subsurface strip for both vintages. The 4D approach consists of performing cross-correlations using collocated CDPs for each sail lines pair. It creates water bottom “cross-image CDP gathers”. The cross-image CDP curvature along offsets is used to compute the water velocity difference between the two vintages. Once a water velocity is inverted for each sail line, the kinematic correction is performed on the pre-migrated datasets. The main difference with conventional approaches is the simultaneous usage of both 4D datasets for estimating the water velocity changes and therefore minimizing the seismic difference in the overburden. The methodology is significantly beneficial for deep-water 4D acquisitions. The correction for such small environmental variations improves the time-lapse data repeatability and is part of the effort for providing high resolution 4D images.

Summary This paper considers the results of summarized integrated geophysical investigations that were carried out from 2006 to 2012. The investigations included common depth point (CDP) seismic reflection survey, over water gravity survey, and differential hydromagnetic exploration with a total work scope of 30 000 linear kilometers. The deep structural tectonic plan, the structural and lithofacies features of the sedimentary cover section on the basic reflecting boundaries, and the features of the seismic sequences and seismic sections on a depth scale have been studied, and geological oil-and-gas zoning of the Northern Barents shelf has been made. Seventy-nine local anticlinal highs have been revealed, and the zones with potential nonstructural hydrocarbon traps have been determined. Due to the lack of huge anticlinal highs in the northern Barents Sea region, nonstructural traps are of interest in studying and replacing the mineral raw material base of Russia, as well as for arranging marine exploration.

Radon filters are often used for removal of multiple reflections from normal move-out-corrected seismic reflection data. In the conventional Radon transform, integration surfaces are hyperbolic rather than linear. This specific hyperbolic surface is equivalent to a parabola in terms of computational expense, but more accurately distinguishes multiples from primary reflections. The forward transform separates seismic arrivals by their differences in travel time move-out. Multiples can be suppressed by an inverse transform of the seismic data. Examples show that multiples are effectively attenuated in pre-stack and stacked seismograms. Based on the parabolic Radon transform, a new method is utilized for missing offset restoration, resampling and regularization of pre-stack individual common depth point (CDP) gathers. The method is also valid for resampling spatially aliased seismic data. Restoration of missing offsets and trace interpolation is an interesting and important problem in seismic data processing. Here we present an application of Radon transform on a multichannel seismic data set from the western continental margin of India (WCMI), which shows remarkable signal enhancement.

This study is aimed at identifying the ultradeep gas reservoir structure and gas‐rich areas in the middle section of the southern margin of the Junggar Basin. Based on high‐precision microgravity data collected from the complex terrain areas of Huxi and Tudong in the middle section of the southern margin of the Junggar Basin, residual gravity anomalies of deep reservoirs were extracted after numerical conversion and various corrections. Combined with comprehensive geological interpretation, favorable areas for natural gas exploration in the Lower Cretaceous and Upper Jurassic were delineated. The results demonstrate that high‐precision microgravity detection offers significant advantages including cost‐effectiveness, environmental friendliness, rapid implementation, and the ability to reflect overall planar effects in optimizing gas reservoir targets. The microgravity results show strong consistency with geological features seismic profile characteristics and gas enrichment patterns observed in drilling wells. Continuous and stable low residual gravity anomalies effectively characterize gas traps and enrichment zones. As a geophysical method for oil and gas exploration, microgravity technology can be integrated with seismic methods or applied independently in areas where seismic data acquisition is challenging. This study significantly expands the application of microgravity detection in natural gas exploration marking its first use in the exploration of deep sandstone gas reservoirs at burial depths exceeding 7300 m. Moreover, in complex mountainous terrain where seismic acquisition and processing are difficult, high‐precision microgravity detection proves to be an effective technique for gas reservoir exploration.