The hydrocarbon-bearing formation of Miano gas field belongs to the Early Cretaceous and it is bounded by two shale intervals, which are considered as maximum flooding surfaces (MFS). The hydrocarbon-bearing interval includes two reservoir units: a tight gas reservoir and its overlying conventional reservoir. Core samples, borehole logs, and well production performance revealed that the two reservoirs present reversed trends in reservoir quality through the gas field without obvious barriers. The average shale volume of the tight gas reservoir changes from 24.3% to 12.2% and the average permeability changes from 32.65 mD to 0.02 mD from the south to north. However, the average effective porosity of the overlaying conventional reservoir increases from 20% to 26% and the average permeability increases from 10 mD to 300 mD. The reversed trends in the two reservoirs lead to challenges in production forecast and development well proposals in the tight gas reservoir. Therefore, reservoir characterization and a predictive reservoir model are essential for further exploitation of Miano gas field. The geological genesis analysis integrating cores, borehole logs, and three-dimensional (3D) seismic data reveals that the producing interval of the tight gas reservoir is tidal-influenced shore facies deposition with intergranular pore space reduced by mineral cementation during burial diagenesis, while the overlaying conventional reservoir is fluvial-influenced deltaic deposition with abundant, well-connected intergranular macropores, which leads to a better reservoir quality. A reservoir model containing both the tight gas reservoir and the conventional reservoir is constructed considering the reservoir nature understanding, and the accuracy of the model is confirmed by reservoir surveillance activities with the simulation model. The study will be critical to the further reservoir development and hydrocarbon production in Miano gas field.

Usually, the signal-to-noise ratio is low and velocity spatial change is severe in areas where fault traps develop. Seismic data processing brings challenges to geophysicists. It is extremely difficult to improve imaging in deep parts were faults harm wave propagation. Traditional pre-stack data migration imaging methods based on common middle points or common shot points are generated by the geophysical theory hypothesis. To overcome such kind of challenge and improve imaging, full azimuth multi-rays pre-stack depth migration was applied in the B block. Full azimuth multi-rays pre-stack depth migration brings a new concept. Rays scan is generated from imaging point toward the surface, leading to a simultaneous emphasis on both continuous structure and discontinuous objects such as small faults and small-scale fractures. In this paper, a comparison was conducted between conventional Kirchhoff pre-stack depth migration and full azimuth multi-rays pre-stack depth migration. Sufficient tests have been carried out in the fault-developed areas. For geological attributes analysis, subsequent processing can be conducted on multi-domain gathers from full azimuth multi-rays pre-stack depth migration according to the request of geologists. Application of this method in B block in the Middle East shows that full azimuth multi-rays pre-stack depth migration can improve the imaging quality of medium and deep layers and improve the imaging of small faults and small-scale fractures. Full azimuth multi-rays pre-stack depth migration can use isotropic and anisotropic velocity models to perform reflection and directional imaging in the local angle domain. Migration radius is defined by both aperture and angle. Information from all azimuths and angles is fully involved in the imaging process, which is beneficial to imaging small faults and fractures. Structural attributes such as dip, azimuth and continuity of the target zone can be obtained directly from gathers after migration. High-quality structural imaging results can be obtained by effective reflection enhancement processing on gathers from full azimuth multi-rays pre-stack depth migration. Diffraction wave enhancement processing can be used for geological fracture prediction. This paper studies the principle of full azimuth multi-rays pre-stack depth migration, compares it with the conventional Kirchhoff prestack depth migration, analyses the advantages of this method in imaging principle and subsequent gathers processing, and applies it to seismic data of the Middle East B Block heterogeneous carbonate reservoir. The result shows that imaging accuracy of full azimuth multi-rays pre-stack depth migration technology is higher, especially in complex structural areas.