SOURCE:

Faculty: Physical Sciences
Department: Applied Geophysics

CONTRIBUTORS:

Adizua, O. Frank
Onwuemesi A. G.
Anakwuba E. K.

ABSTRACT:

OML-23 SOKU is a prospect in the onshore Niger Delta Basin with huge hydrocarbon potential but is plagued with statics problem. This poses a serious challenge for the seismic imaging of the prospect which in turn, would result in erroneous interpretations. To avert these problems, it is imperative for a refraction statics solution to be derived and applied for OML-23, SOKU which has necessitated the study. The aim of the study is to derive a refraction statics solution for 3D seismic data from OML-23, SOKU using the delay time approach. The objectives are to: generate a near-surface model of the prospect in terms of weathering and sub-weathering layer thicknesses and velocities; adapt the near-surface model in deriving a refraction statics solution for the prospect; determine the effectiveness of the statics solution on shot gathers from the prospect; determine the effectiveness of the statics solution on stacked and migrated sections of dataset from the prospect. Seismic noise and amplitude compensation problems which were identified on the seismic dataset were resolved using appropriate processing strategies as their undesirable effects on data quality would hamper the successful actualization of the focal objective for the study. The methodology involved using an integrated (hybrid) approach of inversion of refracted arrivals and up-hole data using special plugins on PROMAX and VISTA software to build a reliable near-surface model of the area. The near-surface model formed the input for deriving the refraction statics solutions for the SOKU dataset. The solutions comprised field statics, refraction statics, 1st and 2nd residual statics which resolved the remnant, uncorrected long and short wavelength statics effect. These solutions were loaded on both software and applied to the dataset using appropriate flow commands to perform the statics correction for the dataset in order to resolve the identified statics problem of the prospect. The result obtained from the near-surface model showed a weathering layer and three consolidated sub-weathering layers. The thicknesses obtained for the weathering, first, second and third consolidated sub-weathering layers ranged from (3 - 18m), (14 – 124m), (62 – 322m) and (248 – 493m) respectively while the velocities ranged from (520m/s), (1614 – 1723m/s), (1708 – 1758m/s) and (1950 – 1976m/s) respectively. At the shot gather processing stage, better alignment of reflection events was achieved; reflection events were exhibiting better continuity and assumed a near-hyperbolic appearance. At the stacking stage, reflectors were properly aligned and continuous with no incidence of mis-ties of reflectors, jittery reflections were moved to their actual position on the common midpoint (CMP) panel. At the migration stage, imaging quality (spatial and temporal resolution) was tremendously enhanced. Reflection continuity across the migrated section was grossly improved and true amplitudes were restored from the post migration results. In conclusion, the derived and applied refraction statics solution had adequately resolved the statics problem of SOKU. This is evident from the enhanced quality of seismic subsurface imaging results achieved. The correct derivation and application of refraction statics for seismic datasets plays a crucial role in enhancing subsurface seismic imaging for accurate geophysical and geological interpretation in the quest to identifying potential and prolific hydrocarbon reservoirs.