Investigating fault shadows in the Niger Delta

Aikulola, Understanding; Olotu, Sam; Yamusa, I.

doi:10.1190/1.3284048

Cited by 10 publications

(6 citation statements)

References 4 publications

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“…These lower-than-normal velocity events in the absence of overpressure and anisotropy which has been accounted for by previous researchers in the study area (Dutta 2002;Aikulola et al 2010;Oni et al 2011;Kanu et al 2014) are regarded as short-path multiple reflection events. The presence of strong subsurface reflectors and contacts between geologic bodies of different seismic properties at the footwall of the main boundary fault (beyond 3 s twoway time) is suggested as the probable causes of this multiple effect.…”

Section: Discussion Of Resultsmentioning

confidence: 71%

“…Aikulola et al (2010) related these chaotic and distorted reflections beyond 3 s two-way time most especially, at the footwall of regional faults to the onset of overpressure. Kanu et al (2014) reviewed the velocity anisotropy considerations using different anisotropy eta values, supported by Zoeppritz's modeling and velocity model updates.…”

Section: Introductionmentioning

confidence: 97%

“…Several authors (Dutta 2002;Aikulola et al 2010;Oni et al 2011;Kanu et al 2014) have investigated the cause of this phenomenon onshore Niger Delta, the reason for this interest being the significant volume of recoverable hydrocarbon prospect beneath the zone, estimated at about 11 billion barrels (Kanu et al 2014). Aikulola et al (2010) related these chaotic and distorted reflections beyond 3 s two-way time most especially, at the footwall of regional faults to the onset of overpressure.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of multiples in onshore Niger Delta: a prelude to fault shadow phenomenon

Azuoko

Ehirim

Ebeniro

et al. 2017

J Petrol Explor Prod Technol

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In this study, multiples have been analyzed as a prelude to fault shadow phenomenon using 3D seismic data from onshore Niger Delta. This involved detailed velocity analysis of a 3D seismic data using semblance plots, from which depth/interval velocity models were generated for two velocity scenarios, the primaries and lower-than-normal velocities in the shadow zone. These velocity models were subsequently used as inputs in prestack depth migration. The result of migration with the lower-thannormal velocities shows that reflections within the shadow zone are coherent, continuous and better aligned than with the primary velocities. This is an indication that these lower-than-normal velocity events have been well accounted for in the shadow zone using these velocities. This result establishes the presence of lower-than-normal velocities in the shadow zone considered as the primary cause of the reflection distortions and misalignment of events observed in the zone, due to multiple reflections. This occurs beyond 3 s two-way time (3800 m), especially at locations corresponding to the footwall of main boundary faults on seismic. This assertion is made based on the fact that all sources of low-velocity events at this depth such as overpressure and anisotropy have been accounted for by previous researchers in the study area and as such, multiple effects are the only plausible low-velocity candidate for the observed reflection distortions in the shadow zone.

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Section: Discussion Of Resultsmentioning

confidence: 71%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Analysis of multiples in onshore Niger Delta: a prelude to fault shadow phenomenon

Azuoko

Ehirim

Ebeniro

et al. 2017

J Petrol Explor Prod Technol

View full text Add to dashboard Cite

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“…Secondly, velocity estimations within the shadow zone did not properly account for this lower than normal velocities during data processing and this is likely responsible for the curtain of noise observed in the shadow zone (Retailleau et al, 2012). Aikulola et al (2010) related chaotic and distortive reflections observed beyond 3 s at the footwall of regional faults in the delta exhibits lower than normal seismic velocities, and associated these to the onset of overpressure regimes. Oni et al (2011), in an onshore study in the Niger Delta, submitted that if anisotropy is taken into consideration and corrected during data preparation and enhancement, seismic imaging could be improved behind the fault.…”

Section: Discussionmentioning

confidence: 99%

“…Aikulola et al (2010) and Opara (2012) investigated overpressure as the possible cause of reflection distortions beyond 3s in Onshore Niger Delta. In a similar study, Oni et al (2011) and Kanu et al (2014) investigated seismic anisotropy as the possible cause of reflection distortions beyond 3s in Onshore Niger Delta.…”

Section: Introductionmentioning

confidence: 99%

Multiples in Onshore Niger Delta from 3D prestack seismic data

Azuoko¹,

Ehirim²,

Ebeniro³

et al. 2017

Int. J. Phys. Sci.

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The presence of multiples has been investigated in Onshore Niger Delta using 3D seismic data. The aim of the study was to investigate the characteristics of reflection events beyond 3s two way time on seismic data behind the boundary faults associated with the shadow zone. This involves detailed velocity analysis on semblance plot panel and accounting for moveouts due to reflections away and within the shadow zone. Interval velocity-depth models were generated from the velocity analysis and analyzed for shadow effect in the data. Results of the study revealed the presence of two velocity scenarios Onshore Niger delta. These are the primary and lower than normal velocities away and within the shadow zone, respectively. The interval velocity-depth models and their overlays on the seismic show a constant increase of velocity with depth for the primary model wh ich seems normal, but this is contrary to the lower than normal velocity model where low seismic velocities predominate beyond 3s two way time (3.8 km), especially at the footwall of the boundary fault. These variations are likely due to the fact that sediments at the footwall of the boundary fault are thicker, compacted and thus yield stronger reflectors than the corresponding sediments away from the faults. The lower than normal velocity reflections in the absence of overpressure and anisotropy, which are also causes of low velocity reflections, are attributed to interbed multiple reflections in the data.

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