Common depth point (CDP)

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.

The Common Depth Point (CDP) Method is a seismic data acquisition and processing technique which transforms field recordings from seismic surveys into pseudo-cross-sectional images of the earth's geologic layering beneath the survey line. Such images are the primary geophysical analysis tools used by explorationists to pinpoint likely drilling locations for oil and gas reservoirs. The CDP Method has evolved from an elementary data enhancement concept in the analog seismic era of the 1950s to a highly sophisticated digital imaging and parameter estimation technique in the 1980s. This paper reviews the history of the method, and its underlying mathematical-physical basis in terms of simple computer simulations of reflection seismic experiments. The method is illustrated with actual examples from several geologic provinces, and the paper closes with a discussion of some limitations of the CDP Stack and possible future directions in seismic imagery.

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.

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 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.

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 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.

In this paper, we demonstrate that Common Mid-Point (CMP) cross-correlation gathers of multi-channel and multi-shot surface waves give accurate phase-velocity curves, and enable us to reconstruct two-dimensional (2D) velocity structures with high resolution. Data acquisition for CMP cross-correlation analysis is similar to acquisition for a 2D seismic reflection survey. Data processing seems similar to Common Depth-Point (CDP) analysis of 2D seismic reflection survey data, but differs in that the cross-correlation of the original waveform is calculated before making CMP gathers. Data processing in CMP cross-correlation analysis consists of the following four steps: First, cross-correlations are calculated for every pair of traces in each shot gather. Second, correlation traces having a common mid-point are gathered, and those traces that have equal spacing are stacked in the time domain. The resultant cross-correlation gathers resemble shot gathers and are referred to as CMP cross-correlation gathers. Third, a multi-channel analysis is applied to the CMP cross-correlation gathers for calculating phase velocities of surface waves. Finally, a 2D S-wave velocity profile is reconstructed through non-linear least squares inversion. Analyses of waveform data from numerical modelling and field observations indicate that the new method could greatly improve the accuracy and resolution of subsurface S-velocity structure, compared with conventional surface-wave methods.

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.

Object of study. The article was devoted to investigation of the depth structure of the Earth’s crust and upper mantle along the Mezen–Timan–Pechora seismic profile (MEZTIMPECH), crossing the southern parts of the Mezen syneclise, the Timan ridge and the Pechora syneclise. Total profile length was 525 km. Materials and methods. In the course of writing the article, the data obtained by performing seismic surveys using the earthquake exchange wave method were used. The processing involved seismic data using the methods of deep seismic sounding, reflected waves, a common depth point, a correlated method of refracted waves, and materials from well geophysical surveys. In interpreting the research results, generalizing models of the deep structure of the territory were employed. Research results. As a result of the interpretation of the records of the method of exchange waves of earthquakes and the subsequent mathematical modeling, a geological and geophysical section was constructed to a depth of about 100 km and a number of seismic boundaries were identified. The pivotal boundaries of the exchange were: Ф0 – the surface of the Riphean folded basement, Ф – the surface of the pre-Riphean crystalline basement, M – the surface of Mohorovich, identified with the roof of the upper mantle. Additionally, horizons K1–K4 – in the crust of the Earth, M1, M2 – in the upper mantle were traced. Four regional geoblocks were distinguished in the seismic section, differing in depth of the basement surface, the Moho sectionand the underlying structural features of the consolidated crust: the Kirov-Kazhim aulacogen, the Vychegda depression, the Timan ridge and the Pre-Ural downfold. Conclusions. The results of deep seismic studies reflected regional features of the structure of the Earth’s crust and were the basis for the construction of tectonic models of large geological objects.

Pycnoclines (layers within ocean waters defined by a rapid change in density, either due to a change in temperature and/or salinity) have been found to produce reflections that appear in seismic data collected on the Amery Ice Shelf (AIS), East Antarctica. The pycnoclines, present due to an ice pump mechanism under the AIS, are clearly visible within the ocean water column beneath the ice shelf. This is evidenced in a 3 km common depth point (CDP) reflection survey undertaken on the eastern side of the AIS. The reflections are unmistakably primary in nature, producing their own multiples in the seismic record. Further processing of other AIS seismic data also reveals reflections at similar arrival times in the ocean water column. While the reflection coefficient (RC) of the ice-water and water-seafloor boundaries are approximately 600 times greater in magnitude than that of these pycnoclines, the pycnocline RCs are 40 times greater in magnitude than the surrounding ocean waters ? sufficient to produce a reflection. The pycnocline reflections correlate well to changes at density interfaces observed by in-situ CTD (conductivity-temperature-depth) data collected under the AIS through a borehole in the ice. Seismic surveys carried out over different field seasons, spanning three years, and observed at different times during the summer seem to indicate that there is a variation in the depth and thickness of the pycnocline layers. One possible reason for this variation is the presence of internal waves at the interface between the density layers.

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 National Geophysical and Solar‐Terrestrial Data Center has recently acquired more than 3400 nautical miles of multichannel common depth point (CDP) seismic reflection data in Alaskan offshore waters.CDP seismic sections are available for a number of survey lines in the Gulf of Alaska, Cook Inlet, and the southeast Bering Sea. In general, the following formats are available: sections and location maps, in sepia or black line; velocity profiles and observer logs, on 35‐mm microfilm; and technical report, shot‐point locations, on microfiche.