3. Estimating subsurface parameter fields for seismic migration: Velocity model building

Jones, Ian F.

doi:10.1190/1.9781560803027.entry3

Cited by 16 publications

(15 citation statements)

References 77 publications

(63 reference statements)

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“…The resulting model provided a much better starting point for gridded tomography. This was performed for the entire Madiela layer and based on non-parametric RMO picking (Brittan and Yuan, 2005;Fruehn et al, 2014;Jones 2015). A total of 200 internal tomographic iterations were run with a cell size of 300x300x20m (XxYxZ).…”

Section: Methodsmentioning

confidence: 99%

Third Time Lucky? Imaging the Dentale Formation Offshore Gabon

Pavlov¹,

Fruehn²,

Sugrue³

et al. 2016

78th EAGE Conference and Exhibition 2016

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Rapid lateral and vertical velocity and thickness variations within Albian carbonates and Aptian evaporites in West African salt basins present considerable problems for seismic imaging and depth modelling. Failure to address these problems has effectively restricted sub-salt exploration success offshore southern Gabon, even with 3D PSDM data processing. Using new 3D data from Dussafu and employing a range of velocity model updating techniques, migration algorithms and geological data we have built a very detailed and accurate velocity model of the complex, stratified Albian carbonate layer. This enabled us to remove some of the artificial deformation evident in earlier processing at Base Salt and below, which resulted from inaccurate velocity models. This successful processing project relied upon close collaboration between the geology and geophysics teams within the operator and the geophysical contractor. This collaboration led to the careful selection of methods to develop a reliable earth model, producing clear seismic images which will be used as a basis for field development.

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Section: Methodsmentioning

confidence: 99%

Third Time Lucky? Imaging the Dentale Formation Offshore Gabon

Pavlov¹,

Fruehn²,

Sugrue³

et al. 2016

78th EAGE Conference and Exhibition 2016

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“…The Transverse isotropy with vertical axis of symmetry, known as vertical transverse isotropy (VTI), is the most common type of anisotropy in sedimentary rocks (Jones et al, 2003). Characterizing the dynamic mechanical properties of rocks in VTI media requires the determination of five independent parameters, which can be stiffness parameters, elastic moduli or the Thomsen's anisotropy parameters.…”

Section: Stiffness Constant Modelingmentioning

confidence: 99%

Anisotropic Geomechanical Characterization of Sojuko Field, Shallow Offshore, Niger Delta

2019

JEES

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Borehole stability and hydraulic fracture issues are a major concern in the economic development of hydrocarbon reserves especially for deep targets which require drilling below well control. Characterizing geomechanical properties along a wellbore provides understanding of the vertical heterogeneity in the mechanical properties of the rocks, both in reservoirs and the bounding non-reservoir formations, and is critical to the operational planning and design of stable wellbores to successfully drill, complete and exploit proven hydrocarbon reserves even at shallow depths. In this work, velocity anisotropy, assuming vertical transverse isotropy with vertical axis of symmetry, was utilized to evaluate important geomechanical properties which include Young's modulus and the Poisson's ratio, in order to accurately determine rock strength and in situ horizontal stresses using geophysical well logs obtained from some wells in the Sojuko field, shallow Niger Delta offshore. The aim was to determine accurate parameters, by consideration of anisotropy, to aid well design and prevent formation failure during future developmental drilling in the field, and the subsequent landing of wells. The starting point was the estimation of the Thomsen's delta anisotropic parameter from analysis of well and seismic interval velocities at a well location, which then aided derivation of the epsilon and gamma anisotropic parameters. The three anisotropy parameters were used in combination with bulk density and sonic log data to determine stiffness constants for the estimation of the geomechanical properties, which subsequently enabled the determination of rock strength and in situ stresses around the wellbore for analysis of rock failure and mudweight requirements for safe and cost effective drilling of the well. Computed in situ minimum horizontal stress in the area varies with depth from 727 psi to 7,500 psi, with an average gradient of 0.69 psi/ft, while the maximum horizontal stress is about 12.27% higher on the average. Minimum average safe drilling mudweight for the well is 0.529 psi/ft, giving an average overbalance of 655 psi mud pressure which is relatively higher in shale than sands. Predicted safe drilling mudweight window ranges from 0.529 psi/ft to 0.713 psi/ft. Comparison of the results with geomechanical data computed with isotropic assumption shows that the nonconsideration of anisotropy results in under prediction of geomechanical data in subsurface formations where velocity anisotropy is present. This has serious safety and cost implication during drilling as most of the Niger Delta deep targets are located in geopressured formations where velocity anisotropy is a perennial problem.

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“…Six tomographic model building updates using Kirchhoff and Beam TTI migration were used in the project (Jones 2010(Jones , 2015. A non-parametric generalised move-out picker (GMO) is used to resolve fine velocity details in the subsurface.…”

Section: Velocity Model Buildingmentioning

confidence: 99%