Seismic Coherence Research Articles

Mass transport deposits and gas hydrate occurrences in the Ulleung Basin, East Sea – Part 1: Mapping sedimentation patterns using seismic coherency

Seismic coherency measures, such as similarity and dip of maximum similarity, were used to characterize mass transport deposits (MTDs) in the Ulleung Basin, East Sea, offshore Korea. Using 2-D and 3-D seismic data several slope failure masses have been identified near drill site UBGH1-4. The MTDs have a distinct seismic character and exhibit physical properties similar to gas hydrate bearing sediment: elevated electrical resistivity and P-wave velocity. Sediments recovered from within the MTDs show a reworked nature with chaotic assemblage of mud-clasts. Additionally, the reflection at the base of MTDs is polarity reversed relative to the seafloor, similarly to the bottom-simulating reflector commonly used to infer the presence of gas hydrates. The MTDs further show regional seismic blanking (absence of internal reflectivity), which is yet another signature often attributed to gas hydrate bearing sediments. At the drill site UBGH1-4, no gas hydrate was recovered in sediment-cores from inside a prominent MTD unit. Instead, pore-filling gas hydrate was recovered only within thin turbidite sand layers near the base of the gas hydrate stability zone. With the analysis of seismic attributes, the seismic character of the prominent MTD (Unit 3) was investigated. The base of the MTD unit exhibits deep grooves interpreted as gliding tracks from either outrunner blocks or large clasts that were dragged along the paleo-seafloor. Similar seismic features were identified on the seafloor although the length of the gliding tracks on the seafloor is much shorter (a few hundred meters to ∼1 km), compared to over 10 km long tracks at the base of the MTD. The seismic coherency attributes allowed to estimate the volume of the failed sediment as well as the direction of the flow of sediment. Tracking the MTD and extrapolating its spatial extent from the 3-D seismic volume to adjacent 2-D seismic profiles, a possible source region of this mass failure was defined ∼50 km upslope of Site UBGH1-4.

Improvements in development strategy for the Stag Oil Field, North West Shelf, Australia—implications for production success and drilling risk minimisation

Located on the North West Shelf of Western Australia, the Stag Oil field has proven to be a prolific reservoir, having produced more than 55 million barrels (MMbbls) of oil since 1998. This has not been without its challenges, however; with premature water breakthrough from injection wells occuring in several wells, potentially stranding large volumes of oil in the ground. Using the multicomponent processing and joint amplitude-versus-offset (AVO) inversion of an ocean bottom cable (OBC) seismic survey acquired in late 2007, new light has been shed on the distribution of unswept oil. This data has led to the succesful drilling of six wells and a marked increase in field production. Additionally, the seismic data has also been used to minimise drilling risks by using seismic coherency to steer the well around potential problems with a significant impact on well costs due to reduction of wellbore problems associated with horizontal drilling in the Muderong shale. To date, four wells have been drilled using this technique, resulting in a significant decrease in non-productive time while drilling during the most recent drilling campaign, which has a significant impact upon the profitability of these late-stage development wells.

Seismic imaging of a fractured gas hydrate system in the Krishna–Godavari Basin offshore India

Gas hydrate was discovered in the Krishna–Godavari (KG) Basin during the India National Gas Hydrate Program (NGHP) Expedition 1 at Site NGHP-01-10 within a fractured clay-dominated sedimentary system. Logging-while-drilling (LWD), coring, and wire-line logging confirmed gas hydrate dominantly in fractures at four borehole sites spanning a 500 m transect. Three-dimensional (3D) seismic data were subsequently used to image the fractured system and explain the occurrence of gas hydrate associated with the fractures. A system of two fault-sets was identified, part of a typical passive margin tectonic setting. The LWD-derived fracture network at Hole NGHP-01-10A is to some extent seen in the seismic data and was mapped using seismic coherency attributes. The fractured system around Site NGHP-01-10 extends over a triangular-shaped area of ∼2.5 km 2 defined using seismic attributes of the seafloor reflection, as well as “seismic sweetness” at the base of the gas hydrate occurrence zone. The triangular shaped area is also showing a polygonal (nearly hexagonal) fault pattern, distinct from other more rectangular fault patterns observed in the study area. The occurrence of gas hydrate at Site NGHP-01-10 is the result of a specific combination of tectonic fault orientations and the abundance of free gas migration from a deeper gas source. The triangular-shaped area of enriched gas hydrate occurrence is bound by two faults acting as migration conduits. Additionally, the fault-associated sediment deformation provides a possible migration pathway for the free gas from the deeper gas source into the gas hydrate stability zone. It is proposed that there are additional locations in the KG Basin with possible gas hydrate accumulation of similar tectonic conditions, and one such location was identified from the 3D seismic data ˜6 km NW of Site NGHP-01-10.

Seismic Response of Power Transmission Tower‐Line System Subjected to Spatially Varying Ground Motions

The behavior of power transmission tower‐line system subjected to spatially varying base excitations is studied in this paper. The transmission towers are modeled by beam elements while the transmission lines are modeled by cable elements that account for the nonlinear geometry of the cables. The real multistation data from SMART‐1 are used to analyze the system response subjected to spatially varying ground motions. The seismic input waves for vertical and horizontal ground motions are also generated based on the Code for Design of Seismic of Electrical Installations. Both the incoherency of seismic waves and wave travel effects are accounted for. The nonlinear time history analytical method is used in the analysis. The effects of boundary conditions, ground motion spatial variations, the incident angle of the seismic wave, coherency loss, and wave travel on the system are investigated. The results show that the uniform ground motion at all supports of system does not provide the most critical case for the response calculations.

Fine-grained Pleistocene deepwater turbidite channel system on the slope of Qiongdongnan Basin, northern South China Sea

Recently, as oil exploitation has become focused on deepwater slope areas, more multi-channel high resolution 2D and 3D seismic data were acquired in the deepwater part of the Qiongdongnan Basin, northern South China Sea. Based on 3D seismic data and coherence time slice, RMS and 3D visualization, a series of deepwater channels were recognized on the slope that probably developed in the late Quaternary period. These channels trend SW–NE to W–E and show bifurcations, levees, meander loops and avulsions. High Amplitude Reflections (HARs), typical for channel–levee complexes, are of only minor importance and were observed in one of the channel systems. Most of the detected channels are characterized by low-amplitude reflections, and so are different from the typical coarse-grained turbidite channels that had been discovered worldwide. The absence of well data in the study area made it difficult to determine the age and lithology of these channels. Using a neighboring drill hole and published data about such depositional systems worldwide, the lithology of these channels is likely to be dominated by mudstones with interbedded thin sandstones. These channels are formed by turbidity currents originated from the little scale mountain river of mid-Vietnam in SW direction and were probably accompanied by a relative sea level drop in the last glacial age. These channels discovered on the northern South China Sea slope are likely to be fine-grained, mud-dominant and low N:G deposits in a deepwater paleogeographic setting.

The design and experimental use of the Mikhnevo 2D small aperture seismic array

The design of a 2D small aperture seismic array (SASA) installed in the central part of the East European Platform (in the area of the village of Mikhnevo, Moscow Oblast’) is discussed. Brief information is provided on the geologic structure of the upper section. The SASA configuration is described along with parameters of the seismological instrumentation used, and the digital seismic data acquisition system. Results are described from a study of the spectral content and the spatial correlation properties of short period microseismic noise and seismic signal coherence. Examples are provided of records of natural and manmade seismic events occurring at different epicentral distances. Experimental data are analyzed to show that this small aperture seismic array can be an effective tool to study low magnitude seismicity in the East European Platform and for solving several other problems arising in contemporary experimental seismology.

Modeling the spatial coherence of seismic surface waves at short propagation distances

Scattering from small, random inhomogeneities in the ground (such as rocks and voids) diminishes the spatial coherence of seismic waves, much as turbulence in the atmosphere diminishes spatial coherence of propagating sound waves. In this paper, modeling of seismic spatial coherence for surface waves propagating over short distances (roughly 50 m to 1 km) and at relatively high frequencies (greater than approximately 1 Hz) is considered. The random inhomogeneities are distributed broadly in size and are described with a quasi‐wavelet (QW) model. For simplicity, we consider propagation of a 2‐D scalar wavefield. Scattering from an individual QW is first calculated using a single‐scattering approximation. Then, the contributions from all randomly placed QWs, including all size classes, are cross‐correlated to find the spatial coherence of the total wavefield. As an example, we consider modeling of seismic coherence at a site in the Mojave Desert with random basaltic inhomogeneities surrounded by sand. The impact of coherence loss on direction‐finding with geophone arrays is discussed.

Application of three-dimensional seismic data to documenting the scale, geometry and distribution of soft-sediment features in sedimentary basins: an example from the Lomre Terrace, offshore Norway

Abstract Three-dimensional seismic data are used to document the geometry, scale and distribution of soft-sediment deformation features in the post-rift succession of the Lomre Terrace, offshore Norway. In the Cretaceous to Upper Oligocene succession a polygonal fault network, developed in the in response to compaction and dewatering of the interval, was mapped using dip and azimuth grid-based attributes. In the same stratigraphic interval a series of chaotic seismic reflection packages are developed which are visualized using a volume-based seismic coherency attribute and interpreted as the seismic expression of mobilized mud masses. Immediately overlying the mobilized mud masses are a series of fault-bounded depressions that are interpreted to have formed in response to deflation of the mobilized mud masses caused by loading of the overlying succession. A series of shallow, curvilinear erosion surfaces are present on the seismic horizon bounding the top of the Pliocene succession and represent iceberg-keel plough marks. This study demonstrates that interpretation and visualization of three-dimensional seismic data coupled with attribute analysis provide valuable insights into soft-sediment deformation features in sedimentary basins, in particular the scale, geometry and distribution of such features and their temporal and spatial inter-relationships.

Stages of Gas Hydrate Evolution on the Northern Cascadia Margin

No abstract available. doi:10.2204/iodp.sd.3.04.2006

Three‐dimensional‐seismic coherency signature of Niger Delta growth faults: integrating sedimentology and tectonics

ABSTRACTThis case study of growth faults and associated deltaic sedimentation in the shallow‐offshore Niger Delta uses an integrated analysis of three‐dimensional (3D)‐seismic coherence facies and wireline data that supports an evaluation of the sedimentary response to delta tectonics. The study area comprises four fault blocks bounded by a set of kilometre‐scale, basinward‐dipping, synsedimentary normal faults. Correlation of highly variable growth stratigraphy across faults was achieved by a systematic visualization and interpretation of series of coherence horizon‐slices: the detection and matching of erosive and depositional patterns (e.g. channels) across faults allowed the establishment of sedimentology‐controlled links between diverse footwall and hanging‐wall growth successions. At the same time, this interpretation approach helped to visualize seismic‐sedimentological and seismic‐geomorphological features survey‐wide at all depth levels. The integration of this extensive 3D database with lithology information from wireline logs provides a powerful tool for subsurface sedimentology interpretation.Synoptic analysis of the 3D‐seismic sedimentology interpretation with stratigraphy based fault‐kinematic analysis using throw vs. depth plots (Th–Z plots) enabled a discussion of the relation between delta tectonics and sedimentary‐system development, and the evaluation of the Th–Z method for subsurface‐lithology prediction. The interpretation results document that both motion analysis of synsedimentary deltaic faults and Th–Z‐based lithology prediction are only feasible when supported by detailed 3D information on palaeoenvironment and palaeotopography at and around studied fault systems. We therefore recommend the use of fast‐track fault‐kinematic and subsurface‐lithology predictions based on Th–Z plots only when supported by comprehensive 3D seismic‐sedimentological interpretations.

Subtle traps prediction using sequence stratigraphy and 3D seismic technology: A case study from Qikou depression in Huanghua basin

Forecasting subtle traps by sequence stratigraphy and 3D seismic data is a sensitive topic in hydrocarbon exploration. Research on subtle traps by geophysical data is the most popular and difficult. Based on the sufficiently drilling data, log data, core data and 3D seismic data, sediment sequence of Qikou depression, Huanghua basin was partitioned by using sequence stratigraphy theory. Each sediment sequence system mode was built. Sediment faces of subtle traps were pointed out. Dominating factors forming subtle traps were analyzed. Sandstone seismic rock physics and its response were studied in Tertiary System. Sandstone geophysical response and elastic modulus vary laws with pressure, temperature, porosity, depth were built. Experimental result and practice shows that it is possible using seismic information forecasting subtle traps. Integrated using geology, log, drilling data, special seismic processing technique, interpretation technique, high precision horizon calibration technique, 3D seismic visualizing interpretation, seismic coherence analysis, attribute analysis, logging-constrained inversion, time frequency analysis, subtle traps object is identified and interpreted. Finally, advantage object of subtle trap in this area was determined. Bottomland sand stratigraphic and lithologic reservoirs in Qinan slope zone have been founded by means of high resolution 3D seismic data field technique, high resolution 3D seismic data processing technique and seismic wave impedence inversion technique.

Prediction of a low tight sandstone reservoir in the Majing gas field, Sichuan Basin, China

The Penglaizheng gas reservoir is a tight sandstone reservoir with strong heterogeneity in the Majing gas field in the Sichuan Basin, China. To identify the reservoir, we attempt to use two measurements: synthesized interval transit time ratio (DT) and apparent fluid recognition index (PF). Gas reservoirs can be recognized effectively by extracting their features from log and seismic data in different sizes. The gas-bearing seismic response of the Penglaizheng reservoir, i.e., 'strong wave amplitude and low wave impedance', obtained from seismic attributes such as amplitude, relative and resolute impedance, and seismic coherence, is observed in an identified profitable area of the Majing gas field. The techniques of seismic attribute analysis and log identification of gas-bearing horizons, acquired from near-tight to tight reservoirs in the Penglaizheng reservoir in the Majing field, can also be used for formations with similar characteristics.

Dual-lateral horizontal wells successfully target bypassed pay in the San Andres Formation, Vacuum field, New Mexico

This case study of the San Andres Formation in the mature Vacuum field, New Mexico, shows how seismic data can be used to target bypassed pay with horizontal wells. These dual-lateral wells were the first attempt at horizontal development in the Vacuum San Andres field and in the San Andres Formation in New Mexico. The primary reservoir facies consist of ramp crest and outer ramp dolomitized peloidal packstones, skeletal and ooid grainstones, and fusulinid packstones. Vertical facies successions form numerous high-frequency carbonate depositional cycles and cycle sets that create distinct reservoir zones. Structural blocks created by small-scale faults (25 ft [8 m] vertical displacement) and bypassed pay located in thin depositional cycles were identified with three-dimensional compressional-wave seismic amplitude and coherency volumes and well data and targeted using medium-radius horizontal wells. Horizontal wells penetrated fault blocks and depositional cycles that were not adequately drained by existing vertical wells.Production curves show a significant increase in production from the horizontal wells and no interference with production from offset vertical wells. This suggests that the faults are partially sealing.

An Algorithm Study on The Seismic Coherence Cube Using Wavelet Transform

AbstractIn this paper, two algorithms of calculating the seismic coherence cube are put forward using wavelet transform, based on the methods of Bahorich et al. and Marfurt etal. The first is a method of calculating the coherence cube from the instantaneous phase of wavelet transform by wavelet functions (or derivative wavelet functions) of simulating seismic wavelet. The second is a method of calculating the coherence cube from the real part and the image part of wavelet transform by above‐mentioned wavelet functions. In order to identify characteristics of small faults in structural interpretation of oilfields, the coherence cube is reconstructed by calculating coherence cube in frequency division. The calculations using realistic data show that the first method is more efficient than the second method for applications to oilfields.

A stochastic approach to site-response component in seismic ground motion coherency model

In order to account for the site-response part of the seismic ground motion coherency for sites of interest, an analytical stochastic methodology is proposed in this paper. By combining the pseudo-excitation method with wave motion finite element simulation techniques, a numerical approach for the computation of the coherency function between observation points is developed firstly. Then the orthogonal expansion method is introduced into this approach to study the effect of the uncertainty in soil properties on the coherency function. Finally some numerical examples are given to show the applicability of the methodology. The computational results demonstrate that the lagged coherency values tend to decrease in the vicinity of the resonant frequencies of the site.

Control of internal structure and fluid-migration pathways within the Barbados Ridge décollement zone by strike-slip faulting: Evidence from coherence and three-dimensional seismic amplitude imaging

The application of three-dimensional seismic reflection and coherence imaging to the study of the decollement zone of the Barbados Ridge accretionary complex has provided new insights into the relationships among internal structure, fluid flow, and previously unrecognized strike-slip faulting. Combined coherence and seismic amplitude imaging of the decollement zone reveal anomalous northeast-trending lineaments parallel to and abutting zones of high- amplitude, negative-polarity reflections. Analysis of these lineaments shows them to be penetrative structures dipping southeast with apparent reverse dip-slip offset. Isopach mapping of the accretionary wedge indicates significant right-lateral displacement across these structures. These faults apparently channel fluid flow within the decollement zone, and the prominent northeast- trending conduits so formed are readily visible as high-amplitude, negative-polarity reflections. Additionally, north-northeast– trending zones of variable coherence and high positive amplitude are inferred barriers to up-structure fluid-migration pathways. Movement along strike-slip structures probably alternates with displacement along the decollement zone. Northeast- trending strike-slip faults extend for >13 km, crossing the length of the survey area and into the incoming oceanic plate. Active arc-oblique strike-slip faulting of the decollement zone beneath the Barbados Ridge accretionary wedge implies a stress regime in that σ 1 is fixed and σ 2 and σ 3 either transpose with time or are nearly equal. This state of stress may be a common occurrence in forearc tectonism and may have led to the formation of many, as yet unrecognized, arc-oblique strike-slip faults at convergent margins.

ABSTRACT: Deepwater Channelized Lobe Complexes : Architecture and Resevoir Potential. Some Insights From One Shallow 3D Seismic Example

Deepwater lobe elements are genetically related to channelized elements. They range the span from simple to complex morphologies and architectures. Simple lobes occur within shallow 3D seismic sections as 1 or 2 high amplitude reflections with a lenticular geometry. Depending on their relative position to parent-channel, they can be defined as crevassesplay, avulsion or terminal lobes. Simple lobe types form excellent reservoirs in both continuity and connectivity with generally good reservoir properties. Unfortunately with limited thickness and spatial extension, they barely pass economic thresholds in deepwater field developments unless associated to channelized reservoirs. Given high sediment influx, simple lobes may evolve to form compound lobes : channelized lobe complexes. These compound lobes are larger in size and more heterogeneous in both lithology and architecture. They consist of an association of different Architectural Elements (A.E.) : (1) basal debris flow, (2) extensive sand sheets dissected and/or overlain by (3) distributary channels with or without (4) levees, the whole capped by (5) hemipelagites. The distributary channels radiate from one single point (avulsion, crevasse or channel-mouth). They are narrow in proximal areas, may develop relatively thick levees and are mostly filled with relatively coarse-grained material. Downdip, distributary channels are wider with lower levees, if present, and are barely visible on seismic sections. Combination of various type of seismic attributes, mainly amplitude and coherency, mapping applied to one shallow example allow the identification and characterization of the A.E. and a better understanding of the architecture of these compound lobes.

Analytical approach for evaluation of the seismic ground motion coherency function

In this paper, a stochastical approach for the investigation and the comprehension of the spatial variation of the seismic motions is presented. For this purpose, a coherency function analytical model is proposed. The approach regards the seismic motion as the combination of a traveling wave on the site (coherent component) and a zero mean randomizing factor that introduces an incoherence effect. The soil parameters as fundamental frequency and damping coefficient are integrating by modeling the coherent component with the commonly used Kanai-Tajimi power spectral density. The parametric analysis of the model shows an increase of the coherency with the increase of (i) the apparent propagation velocity of the motions on the ground surface, and (ii) the correlation length. On the other hand, the coherency decrease with the increase of: (i) the frequency content of the motion, (ii) the separation distance between stations and (iii) the scattering parameter which is the randomizing factor standard deviation. Finally, in order to test the proposed model prediction, its coherency function is compared to empirical results obtained on the EPRI LSST array in Lotung, Taiwan (Abrahamson NA, Shneider JF, Stepp JC. Earthquake Spectra 1991; 7:1–28). The comparison shows that the proposed model fits the spatial variability of seismic motions on Lotung site. In the absence of spatially recorded seismic data on a site, the proposed analytical model can be utilised for the description of the spatial variability of the seismic motions for the seismic response analysis of structures with large dimensions as pipes, bridges, tunnels…etc.

Narrow‐band spectral analysis and thin‐bed tuning

Running window seismic spectral decomposition has proven to be a very powerful tool in analyzing difficult‐to‐delineate thin‐bed tuning effects associated with variable‐thickness sand channels, fans, and bars along an interpreted seismic horizon or time slice. Unfortunately, direct application of spectral decomposition to a large 3‐D data set can result in a rather unwieldy 4‐D cube of data. We develop a suite of new seismic attributes that reduces the input 20–60 running window spectral components down to a workable subset that allows us to quickly map thin‐bed tuning effects in three dimensions. We demonstrate the effectiveness of these new attributes by applying them to a large spec survey from the Gulf of Mexico. These two thin‐bed seismic attributes provide a fast, economic tool that, when coupled with other attributes such as seismic coherence and when interpreted within the framework of geomorphology and sequence stratigraphy, can help us quickly evaluate large 3‐D seismic surveys. Ironically, in addition to being more quantitatively linked to bed thickness, the thin‐bed attributes described here allow us to analyze thicker features than the conventional instantaneous and response frequencies, which cannot calculate the spectral interference between two well‐separated reflectors.

ABSTRACT: Jonah Field Area: Seismic Coherency Cube Technology Used to Define Trap Boundaries and Stratigraphic Features

ment wells at Jonah Field. Jonah Field, Sublette County, Wyoming, is expected to produce at least 1.5 TCF of natural gas from lenticular, over-pressured, tight formation gas fluvial sandstones of the Cretaceous-age Lance Formation. Depth of production is 7,500 to 12,400 feet and the gross producing interval is 1500 to 3200 feet. Jonah was indicated to be a significant field in early 1993 (Robinson, 2000) and now produces more than 400 MMCFD from more than 200 wells (Fig. 1). In-fill drilling on 40-acre spacing has been underway since mid-2000. Entrapment may result from a combination of dip reversal and fault zone deformation associated with faults that intersect up dip to form a wedge-shaped compartment. Apparent throw on the bounding faults is variable, but commonly is less than 200 feet.