Are bright spots always hydrocarbons? A case study in the Taranaki Basin, New Zealand

2020 ◽  
Vol 8 (4) ◽  
pp. SR45-SR51
Author(s):  
Peter Reilly ◽  
Roberto Clairmont ◽  
Heather Bedle
Keyword(s):  
New Zealand ◽  
High Amplitude ◽  
Seismic Survey ◽  
Bright Spot ◽  
Temporal Region ◽  
Cross Sectional ◽  
Seismic Amplitude ◽  
Bright Spots ◽  
Seismic Amplitudes ◽  
Seismic Anomalies

In the shallower regions of the 3D Nimitz seismic survey, there exist multiple interesting bright seismic amplitude anomalies. These anomalies, or funny looking things, occur in a confined spatial and temporal region of the seismic. They have a concave-up seismic appearance along the cross section. Bright seismic amplitudes can be a direct hydrocarbon indicator, or they can be representative of strong lithologic contrasts and/or acquisition artifacts. We have set out to investigate misinterpreted seismic anomalies along cross-sectional lines. Therefore, we apply seismic attributes to indicate that these bright spot features, which we interpret to be submarine gullies looking along time-slice intersections, can possibly be mistaken for hydrocarbon anomalies in a cross-sectional view. However, we cannot fully rule out the presence of hydrocarbons because it is common for gas sands to create similar anomalies. Previously drilled wells within the survey (Korimako-1 and Tarapunga-1) point to a lack of hydrocarbon potential in the subsurface. Although it is possible that these bright spots are due to hydrocarbon presence, we develop a more likely hypothesis: The lithology of the interfluve sediments is similar to the gully-margin drapes but differs from the gully sediment fill. Funny looking thing (FLT): Submarine gullies Seismic appearance: High-amplitude spotted features Alternative interpretations: Lithologic anomalies, gas seeps, bright spots Features with a similar appearance: Gas accumulation, sediment fills in limestone paleocaves Formation: Giant Foresets Formation Age: Pleistocene Location: Taranaki Basin, New Zealand Seismic data: Nimitz 3D (cropped volume) Analysis tools: Curvature, instantaneous frequency, and sweetness attributes; well reports

Using relative geologic time to constrain CNN-based seismic interpretation and property estimation

Geophysics ◽  
2021 ◽  
pp. 1-44
Author(s):  
Aria Abubakar ◽  
Haibin Di ◽  
Zhun Li
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Seismic Interpretation ◽  
Seismic Survey ◽  
Geologic Time ◽  
Seismic Amplitude ◽  
Property Estimation ◽  
Constrained Learning ◽  
Seismic Amplitudes ◽  
Multiplicative Regularization

Three-dimensional seismic interpretation and property estimation is essential to subsurface mapping and characterization, in which machine learning, particularly supervised convolutional neural network (CNN) has been extensively implemented for improved efficiency and accuracy in the past years. In most seismic applications, however, the amount of available expert annotations is often limited, which raises the risk of overfitting a CNN particularly when only seismic amplitudes are used for learning. In such a case, the trained CNN would have poor generalization capability, causing the interpretation and property results of obvious artifacts, limited lateral consistency and thus restricted application to following interpretation/modeling procedures. This study proposes addressing such an issue by using relative geologic time (RGT), which explicitly preserves the large-scale continuity of seismic patterns, to constrain a seismic interpretation and/or property estimation CNN. Such constrained learning is enforced in twofold: (1) from the perspective of input, the RGT is used as an additional feature channel besides seismic amplitude; and more innovatively (2) the CNN has two output branches, with one for matching the target interpretation or properties and the other for reconstructing the RGT. In addition is the use of multiplicative regularization to facilitate the simultaneous minimization of the target-matching loss and the RGT-reconstruction loss. The performance of such an RGT-constrained CNN is validated by two examples, including facies identification in the Parihaka dataset and property estimation in the F3 Netherlands dataset. Compared to those purely from seismic amplitudes, both the facies and property predictions with using the proposed RGT constraint demonstrate significantly reduced artifacts and improved lateral consistency throughout a seismic survey.

GOLDEN BEACH: A BRIGHT SPOT

1978 ◽  
Vol 18 (1) ◽  
pp. 109
Author(s):  
R. B. Mariow
Keyword(s):  
Seismic Data ◽  
High Amplitude ◽  
Late Eocene ◽  
Polarity Reversal ◽  
Bright Spot ◽  
Areal Extent ◽  
Water Contact ◽  
Bright Spots ◽  
Gippsland Basin ◽  
Seismic Reflector

The Golden Beach closed anticlinal structure lies five kilometres offshore in the Gippsland Basin. Golden Beach 1A was drilled in 1967 near the crest of the structure and intersected a gas column of 19 m (63 feet) at the top of the Latrobe Group (Late Eocene) where most of the hydrocarbon accumulations in the Gippsland Basin have been found. The gas-water contact lies at a depth of 652 m (2139 feet) below sea level.On seismic data recorded over the structure, a high amplitude flat-lying event was interpreted as a bright 'flat spot' at the gas-water contact. Reprocessing of the seismic data enhanced the bright spot effect and enabled the areal extent of the gas zone to be mapped. The presence of the gas also leads to a polarity reversal of the top of the Latrobe Group seismic reflector over the gas accumulation.Seismic data from other structures containing hydrocarbons in the Gippsland Basin support the concept that bright spots and flat spots are more likely to be associated with gas than with oil accumulations, and that the observed bright spot effect decreases with increasing depth.

Seismic detection of overpressuring and fracturing: An example from the Qaidam Basin, People’s Republic of China

Geophysics ◽  
1993 ◽  
Vol 58 (10) ◽  
pp. 1532-1543 ◽  
Author(s):  
Robert J. Paul
Keyword(s):  
Oil And Gas ◽  
Qaidam Basin ◽  
High Amplitude ◽  
Seismic Survey ◽  
Low Velocity ◽  
Velocity Anomaly ◽  
Deep Well ◽  
Significant Difference ◽  
Seismic Amplitudes ◽  
Definition Of

Shallow hydrocarbon reserves were discovered in 1959 in the Nan Yi Shan structure located near the western corner of the Qaidam Basin. The first successful deep well encountered an overpressured zone at 3000 m that resulted in a well blowout. To improve the structural definition of the field and delineate the overpressured layer a 3-D seismic survey was conducted. A region of anomalous seismic time sag associated with fracturing and small quantities of oil and gas was identified on the northwest plunging nose of the Nan Yi Shan anticline. The distribution of stacking (NMO) velocities in this region was regarded as abnormal; stacking velocities derived on the steeply dipping flanks adjacent to the sag anomaly were found to be slower than those on the shallower crest. Ray‐trace modeling of a buried low‐velocity anomaly provided a possible geometric solution to explain both the time variant nature of the sag and the unusual stacking velocity signature associated with it. A significant difference in seismic and sonic traveltimes was also observed for wells that penetrated the sag region and was attributed to localized fracturing. In a deeper interval, seismic amplitudes were used to identify gas‐saturated fracture porosity and to describe the spatial limits of overpressuring within a thin‐bed reservoir. Wells drilled through high‐amplitude anomalies encountered overpressuring, those drilled in a region of moderate seismic amplitude tested significant quantities of gas, and wells located outside the region of good coherent signal encountered poor or no hydrocarbon shows. These results demonstrate that with good quality seismic data and sufficient lateral and vertical resolution, thin fractured hydrocarbon‐bearing reservoirs can be delineated and overpressure zones identified.

Geological origins of seismic bright spot reflections in the Ordovician strata in the Halahatang area of the Tarim Basin, western China

2018 ◽  
Vol 55 (12) ◽  
pp. 1297-1311 ◽  
Author(s):  
Wei Yang ◽  
Xiaoxing Gong ◽  
Wenjie Li
Keyword(s):  
Tarim Basin ◽  
Oil And Gas ◽  
High Amplitude ◽  
Hydrothermal Activity ◽  
Hydrocarbon Exploration ◽  
Western China ◽  
Bright Spot ◽  
Gas Reservoirs ◽  
Seismic Section ◽  
Bright Spots

Anomalously high-amplitude seismic reflections are commonly observed in deeply buried Ordovician carbonate strata in the Halahatang area of the northern Tarim Basin. These bright spots have been demonstrated to be generally related to effective oil and gas reservoirs. These bright spot reflections have complex geological origins, because they are deeply buried and have been altered by multi-phase tectonic movement and karstification. Currently, there is no effective geological model for these bright spots to guide hydrocarbon exploration and development. Using core, well logs, and seismic data, the geological origins of bright spot are classified into three types, controlled by karstification, faulting, and volcanic hydrothermal activity. Bright spots differing by geological origin exhibit large differences in seismic reflection character, such as reflection amplitude, curvature, degree of distortion, and the number of vertically stacked bright spots in the seismic section. By categorizing the bright spots and the seismic character of the surrounding strata, their geological origins can after be inferred. Reservoirs formed by early karstification were later altered by epigenetic karstification. Two periods of paleodrainage further altered the early dissolution pores. In addition, faults formed by tectonic uplift also enhanced the dissolution of the flowing karst waters. Some reservoirs were subsequently altered by Permian volcanic hydrothermal fluids.

EXPLORATION OPPORTUNITIES, EAST COAST BASIN, NEW ZEALAND

2000 ◽  
Vol 40 (1) ◽  
pp. 39
Author(s):  
J.B. Frederick ◽  
E.J. Davies ◽  
P.G. Smith ◽  
D. Spancers ◽  
T.J. Williams
Keyword(s):  
New Zealand ◽  
Late Miocene ◽  
Joint Venture ◽  
East Coast ◽  
High Amplitude ◽  
Petroleum Exploration ◽  
Early Miocene ◽  
Seismic Survey ◽  
Seismic Events ◽  
Submarine Fan

The Westech-Orion Joint Venture holds onshore Petroleum Exploration Permit 38329 and offshore PEPs 38325, 38326 and 38333 in the East Coast Basin, New Zealand. The Joint Venture holds 24,117 km2 covering Hawkes Bay and the Wairarapa shelf.The Westech-Orion Joint Venture has drilled six exploratory wells and five appraisal wells in the onshore East Coast Basin over a two year period. All wells encountered significant gas shows, with two wells discovering hydrocarbons in potentially commercial volumes. Each well was drilled on the crest of a seismically mapped structure, characterised by asymmetric folding over a northwest dipping thrust fault.Prior to this drilling program, the reservoir potential of the Wairoa area was inferred to be dominated by turbidite sandstones of the Tunanui and Makaretu formations (Mid-Late Miocene). The new wells show that the Mid Miocene and parts of the Early and Late Miocene pinch out across the 'Wairoa High'.One of the primary onshore reservoirs is the Kauhauroa Limestone (Early Miocene), a bryozoan-dominated, tightly packed and cemented limestone with dominantly fracture porosity. The other primary reservoir is the Tunanui Sandstone (Mid Miocene), which in well intersections to date comprises medium-thickly bedded sandstone, with net sand typically 40%. The sands have high lithic content, and are moderately sorted and subangular-subrounded.Abnormally high formation pressures were encountered in all wells, ranging up to 3,400 psi at 1,000 m. Crestal pressure gradients commonly exceed 70% of the lithostatic pressure gradient, despite the relative proximity to outcrop. The overpressure may reflect relatively young uplift of fossil pressures, with insufficient time for pressure equilibration within a generally overpressured system.The prospectivity of the area has been highgraded by recent maturation and reservoir studies in Hawkes Bay and by gas discoveries in Westech-Orion wells onshore northern Hawkes Bay. Maturation studies identified nine kitchen areas with oil migration commencing in the Late Miocene. Seismic stratigraphy and correlation with onshore wells identified offshore submarine fan deposits of Eocene, Early Miocene, Mid Miocene and Pliocene age.A 594 km2 exploration 3D seismic survey was acquired in Hawke Bay in April 1999, and 685 km of 2D seismic were acquired in March 2000. Preliminary interpretation of the 3D survey has yielded five prospects, each covering 20–90 km2. One prospect is a lowstand fan identified by stacked mounding and bidirectional downlap, correlated with the onshore Mid Miocene Tunanui Sandstone. High amplitude seismic events of Mid-Late Miocene ages are inferred to be pulses of submarine fan development, in places associated with direct hydrocarbon indicators (DHIs). High amplitude seismic events in the Pliocene include a package of high amplitude seismic reflectors interpreted as structurally trapped DHI truncated by a major unconformity.

scholarly journals Shallow Gas Prospect Evaluation in Shahbazpur Structure Using Seismic Attributes Analysis - a Case Study for Bhola Island, Southern Bangladesh

2016 ◽  
Vol 64 (2) ◽  
pp. 135-140
Author(s):  
Morshedur Rahman ◽  
SM Mainul Kabir ◽  
Janifar Hakim Lupin
Keyword(s):  
High Amplitude ◽  
Seismic Attributes ◽  
Bright Spot ◽  
Deep Basin ◽  
Seismic Attribute ◽  
Spot Detection ◽  
Bright Spots ◽  
Amplitude Anomaly ◽  
Gas Fields ◽  
Migration Pathways

Shahbazpur structure is located in the southern Part of the central deep basin in the Hatia trough, where lie all the largest Gas fields of Bangladesh. A method is established to delineate the structural mapping precisely by interpreting four 2D seismic lines that are acquired over Shahbazpur structure. Moreover direct hydrocarbon indicators (DHI) related attributes are analyzed for further confirmation for presence of hydrocarbon. To do this synthetic seismogram generation, seismic to well tie, velocity modelling and depth conversion are performed. A limited number of seismic attributes functions that are available in an academic version of Petrel software are applied to analyze attributes. Seismic attribute analyses that are used in this interpretation mainly are associated to bright spot detection. Presence of bright spots or high amplitude anomaly over the present Shahbazpur structure, reservoir zone are observed. This signature will play a very important role in next well planning on the same structure to test the shallow accumulation of hydrocarbon. For better understanding of this shallow reserve, it is suggested to acquire 3D seismic data over Shahbazpur structure which will help to evaluate the hydrocarbon accumulation and to identify gas migration pathways. Dhaka Univ. J. Sci. 64(2): 135-140, 2016 (July)

Characterization of shallow high-amplitude seismic anomalies in the Hoop Fault Complex, Barents Sea

2017 ◽  
Vol 5 (4) ◽  
pp. T607-T622 ◽  
Author(s):  
Satinder Chopra ◽  
Ritesh Kumar Sharma ◽  
Graziella Kirtland Grech ◽  
Bent Erlend Kjølhamar
Keyword(s):  
Barents Sea ◽  
Rock Physics ◽  
High Amplitude ◽  
Data Types ◽  
Impedance Inversion ◽  
To Come ◽  
Seismic Amplitudes ◽  
Diverse Data ◽  
Seismic Anomalies ◽  
Elastic Impedance

The shallow migrating hydrocarbon fluids in the western Barents Sea are usually found to be associated with high seismic amplitudes. We have attempted to characterize such shallow high-amplitude anomalies in the Hoop Fault Complex area of the western Barents Sea. The workflow is devised for discrimination of anomalies that are associated with the presence of hydrocarbons from those that are not, and quantifying them further includes the computation of a set of seismic attributes and their analyses. These attributes comprise coherence, spectral decomposition, prestack simultaneous impedance inversion, and extended elastic impedance attributes, followed by their analysis in an appropriate crossplot space, as well as with the use of rock-physics templates. Finally, we briefly evaluate the futuristic efforts being devoted toward the integration of diverse data types such as P-cable seismic as well as controlled-source electromagnetic data so as to come up with an integrated assessment for the prospects and to mitigate risk.

Poroelastic analysis of amplitude-versus-frequency variations

Geophysics ◽  
2009 ◽  
Vol 74 (6) ◽  
pp. N41-N48 ◽  
Author(s):  
Haitao Ren ◽  
Gennady Goloshubin ◽  
Fred J. Hilterman
Keyword(s):  
Low Frequency ◽  
Bright Spot ◽  
Frequency Dependent ◽  
Low Frequencies ◽  
Amplitude Variation With Offset ◽  
Seismic Amplitude ◽  
Nondispersive Medium ◽  
Seismic Anomalies ◽  
Frequency Variations ◽  
Lower Frequencies

Although significant advancement has occurred in the interpretation of seismic amplitude-variation-with-offset (AVO) anomalies, a theory is lacking to guide the interpretation of frequency-dependent seismic anomalies. Using analytic equations and numerical modeling, we have investigated characteristics of the normal-incident reflection coefficient (NI) as a function of frequency at an interface between a nondispersive medium and a patchy-saturated dispersive medium. Because of velocity dispersion, the variation of NI magnitude is divided into three general classes. These classes are (1) low-frequency dim-out reservoirs, in which NI magnitude decreases toward lower frequencies; (2) phase-shift reservoirs, in which NI is a small negative value at low frequencies but becomes positive at higher frequencies; and (3) low-frequency bright-spot reservoirs, in which NI magnitude increases toward lower frequencies. This classification could provide insight for frequency-dependent seismic interpre-tation.

THE SEISMIC REFLECTION RESPONSE TO CHANGES IN PRESSURE

2002 ◽  
Vol 42 (1) ◽  
pp. 571
Author(s):  
B. Evans ◽  
A. Pauli
Keyword(s):  
Seismic Reflection ◽  
Pressure Change ◽  
Seismic Survey ◽  
Bright Spot ◽  
Overburden Pressure ◽  
Unconsolidated Sand ◽  
Volumetric Assessment ◽  
Bright Spots ◽  
Zero Offset ◽  
Water Saturated

Hydrocarbons are often interpreted using seismic attributes, the most common being high anomalous amplitudes or bright spots. Seismic data processing and interpretation is involved in enhancing such anomalies, thereby improving the interpretation for both optimised drilling and volumetric assessment. However, not all bright spots are hydrocarbons since there have been occasions when an economically drillable bright spot unexpectedly produces a dry hole. This paper discusses the first laboratory-based experiments aimed at understanding seismic reflection effects caused by changes in pressure. Water-saturated unconsolidated sand in an unconfining container was pressured from room pressure to over 2 MPa in step manner and then reduced back to room pressure. After each step in application of overburden pressure change, a zero offset 3D seismic survey was performed using ultrasonic transducers. This approach was repeated after the injection of air, to observe the seismic response to gas under changing pressure.The velocity of sand increased as a function of pressure until a value of approximately 1 MPa was attained, when fracturing became apparent. Upon pressure reduction below 2MPa, fracture healing became apparent; there were also rapid changes in reflection amplitudes due to changes in pressure. It is under high pressure that preferential alignment of parallel grains at specific distances relative to the seismic wavelength may result in ‘seismic tuning’, and apparent bright spots. It was noted that a pressure increase caused anti-clockwise rotation of the AVO fluid line; this may provide an indication of whether a change in seismic character is a result of a pressure or gas reduction. Some apparent bright spots within sand/shale sequences may also result from seismic tuning effects developed at specific seismic wavelengths, rather than from the presence of hydrocarbons; the sense of rotation of the fluid line may also help to differentiate between a pressure change or gas reduction.

3-D Seismic Mapping and Amplitude Analysis: A Gulf of Mexico Case History

1992 ◽  
Vol 10 (4-5) ◽  
pp. 259-280 ◽  
Author(s):  
Robert L. Kidney ◽  
Ronald S. Silver ◽  
H.A. Hussein
Keyword(s):  
Gulf Of Mexico ◽  
Seismic Data ◽  
Seismic Survey ◽  
Rock Properties ◽  
Amplitude Analysis ◽  
Seismic Amplitude ◽  
Energy Company ◽  
Amplitude Anomaly ◽  
Key Steps ◽  
Seismic Anomalies

Utilization of 3-D seismic data and Direct Hydrocarbon Indicators led to the successful drilling of appraisal and development wells in the Gulf of Mexico block South Timbalier 198 (ST 198). These seismic technologies, which are routinely used by Oryx Energy Company, significantly reduced the time and cost to appraise the ST 198 discovery. Based on 2-D seismic mapping, a Pliocene Lower Buliminella (L BUL) prospect was drilled in ST 198. Although the expected reservoir was not found, an Upper Buliminella (U BUL) gas sandstone was encountered. An appraisal well of the U BUL interval confirmed this discovery. Following the drilling of these two wells, it became apparent that the structural complexities and the seismic amplitude anomalies of the area could not be adequately resolved using the 2-D seismic grid. A 3-D seismic survey was shot to delineate the discovery and evaluate the remaining potential of the South Timbalier Block 198 (ST 198). Direct Hydrocarbon Indicators (DHIs), which are seismic anomalies resulting from the hydrocarbon effect on rock properties, are generally expected from these age sands. While the 3-D survey shows a seismic amplitude anomaly associated with the U BUL reservoir, the areal extent of the seismic anomaly did not match the findings of the two wells. A DHI study was performed to determine if this inconsistency could be explained and if the amplitude anomaly could be used in the well planning. The two key steps which confirmed that this amplitude anomaly is a DHI were properly calibrating the seismic data to the well control and determining the theoretical seismic response of the gas sandstones. The DHI study along with the 3-D mapping led to the successful development of the ST 198 U BUL reservoir and to setting up a successful adjacent fault block play. Finally, 3-D mapping also identified a L BUL trap updip from the original L BUL prospect which resulted in a successful drilling effort.

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