The Naoetsu Basin is one of several oil- and gas-producing provinces in Japan where thick Neogene strata are deposited, and oil and gas are produced from both onshore and offshore shelf areas. It is believed that the Naoetsu Basin extends into deep-water areas, but exploration activities were limited until 2000, except for regional 2D seismic surveys. After acquisition of a 3D seismic survey in 2001, the first two wells were drilled in 2004 in the deep-water area of the Naoetsu Basin. One well encountered an oil zone. Multi-dimensional basin modelling was conducted to understand the petroleum system in the deep-water area of the Naoetsu Basin before and after the wells were drilled. The accuracy of basin modelling depends on the accuracy of the input data as well as the calibration process. However, even after the drilling campaign, only two wells were available in the deep-water area of the Naoetsu Basin. Therefore, the integration of various kinds of data, information and different techniques, such as 3D seismic, sedimentological and geochemical data, was carried out in this study. Development of sandstone networks, as well as the presence of major and minor faults, was identified on 3D seismic data. Oil and gas migration were constrained by geochemical data, such as carbon isotope on gases collected at the sea bottom and fluid inclusion chemistry. Understanding of the petroleum system was increased significantly by this kind of integration, although the deep-water area of the Naoetsu Basin still remains a frontier area for oil and gas exploration. It was found that the petroleum system active in the deep-water area of the Naoetsu Basin is very effective. Even though maturation of the source rock has occurred only since the Pliocene, oil and gas generated and migrated very rapidly, first horizontally along sandstone networks and then vertically through faults reaching a level just below the sea bottom, with the result that the hydrocarbon trap has leaked.

We studied in detail the calcareous nannofossil biostratigraphy of the upper Pliocene to Quaternary sequences in the Osugozawa route of Gojome area, Aikawa and Komasugawa routes of the Oga peninsula, and two oil exploration wells of NKH-and located in Honjo area, Akita Prefecture, Japan. The Pliocene/Pleistocene boundary redefined at the base of Gelasian Stage was identified in the lower part of the Sasaoka Formation in the Osugozawa route. The base of Calabrian stage, formerly considered as the Pliocene/Pleistocene boundary, was also identified in the lower part of the Kitaura Formation in the Oga Peninsula, based on magneto-and nannofossil bio-stratigraphy. Pliocene to Quaternary formations in the Akita area were correlated to those in the Japan Sea side area.We also revealed the tectonic movements along the southern coast of Akita Prefecture on the basis of the nannofossils obtained from drill cuttings and the subsurface geology of the area. The results clarified that the Kita-Yuri thrust faults were active between . and . Ma. Paleodepth of western Akita Prefecture were also changed from bathyal to shallow marine environments in . Ma, a consequence of both fault activity and the climate crush associated with drastic latest Pliocene cooling.

To generate refined depth structure for a very gentle Cretaceous reservoir on an oil field offshore Abu-Dhabi, we conducted channel velocity modelling and prestack depth migration (PSDM). The target reservoir structure on a vintage prestack time migration (PSTM) contains pull-up and push-down artefacts, induced by a couple of overburden channel velocity fills. These artefacts hindered correct representation of gentle depth structure at the target. Detailed interpretation on the PSTM volume delineates overburden channels in three upper Cretaceous formations. One of them, Fiqa channel, generates small pull-up and the others, Halul and Lafan channels generate push-down below each formation, caused by higher and lower velocity channel fills, respectively. These artefacts overlapped at some locations. Analysis of synthetic PSTM stack from forward modelling reminded us that a low-velocity channel produces obvious push-down below the channel. The shape of push-down become smaller but wider with depth and offset. The resulted push-down in full-offset stack also changed with depth. A "true" channel velocity and implementation of PSDM eliminates push-down at all depths and offsets. Bearing in mind the phenomenon confirmed on the forward modelling, we first produced channel velocity model for the target field data. With the assumption that the depth structure at a layer just below channels is flat, time thickness of channel and the amount of push-down at the layer below the channel could determine the channel velocities. Then, we estimated three channel velocities by channel time thicknesses and the amount of pull-up/push-down at the top Mid-Cretaceous shale, Nahr Umr formation that located just below these channels. On the overlapped area, a linear inversion provided each channel velocity. An application of PSDM with the channel velocity model successfully mitigated the artefact at target depth structure. Introduction We sought refined reservoir structure through channel velocity modeling and PSDM at the target oil field, located about 60km off the coast of Abu Dhabi. The lower Cretaceous reservoir (Figure 1) structure consists of a couple of very gentle domal structure-highs, whose average dips are 1-degree and heights are less than 100ft. Since subtle difference of the reservoir depth made significant change in oil saturation and production rate, identification of such structure highs is critical for seeking enhanced productivity and oil recovery. Although vintage PSTM volume produced in 2004 showed good quality to provide more accurate reservoir structure and led to success on some wells, the time structure could contain as much as 10ms (60ft with 12,000ft/s) artefacts at the reservoir, caused by overburden channel velocity fills (Figure 2). These artefacts hindered correct representation of reservoir structure and gave rise to depth uncertainty. We realized that generation of precise reservoir structure necessitates discrimination between artefacts and true structural events. There are some publications that introduce solutions of these problems. Armstrong et. al., (2000) introduced a methodology of compensating artifacts using the amount of the pull-up and push-down changed with depth on post-migrated time volume. Fujimoto et. al., (2007) removed both pull-up/push-down and PSTM velocity artifacts through high-resolution tomography and PSDM.

There is no doubt that 3D seismic data make a powerful contribution to field development. Less obvious, and often controversial, is the critical step of defining level of seismic survey effort required to achieve the objectives for field development. An over-specified seismic survey could be costly, and an under-specified seismic survey would not achieve the objectives. A 3D OBC pilot seismic survey was conducted in a carbonate field of offshore Abu Dhabi, United Arab Emirates with the main objectives: (1) to demonstrate imaging of the Upper Jurassic Arab formation; and (2) to optimize survey parameters for future seismic surveys. In this highly-specified pilot seismic survey, two orthogonal 3D datasets were acquired, and one swath 3D dataset was simulated by sampling shot-points parallel to receiver-lines. The data density is significantly different among these datasets, however the offset and azimuth distributions are similar. Twenty-three cubes were generated from these datasets by decimating the full data. Unless particular reasons necessitated change, the same processing parameters were applied to all cubes to minimize any differences due to processing effects. The relationship between data quality and operational effort was determined by analyzing twenty-three cubes qualitatively and quantitatively from the structure interpretability point of view. The main findings are: (1) higher specification cubes successfully imaged the main Upper Jurassic Arab reflectors; (2) higher specification cubes require higher operational effort; (3) in general, higher specifications improve data quality; (4) however, data quality eventually reaches a plateau even with increasing specifications; and (5) certain cubes are more efficient, they provide higher data quality with lower operational effort. The methodology and results will be used to assist in establishing and optimizing survey parameters for future seismic surveys offshore Abu Dhabi, United Arab Emirates.

Petroleum exploration without seismic method: