The Yurihara oil and gas field is located on the southern edge of Akita Prefecture, northeastern Japan. In this area, drilling, surface geological surveys and many seismic surveys have been used to investigate the geological structure. Wells drilled into the Nishikurosawa Basalt Group (NBG) of Miocene age found oil and gas reservoirs at depths of 1.5–2 km. Oil and gas are now being produced commercially and further exploration is required in the surrounding areas. However, since the neighbouring areas are covered with young volcanic products from the Chokai volcano, and have a rough topography, the subsurface distribution of the NBG must be investigated using other methods in addition to seismic reflection. According to the well data, the resistivity of the NBG is comparatively higher than that of the overlying sedimentary formations, and therefore the magnetotelluric (MT) method is expected to be useful for the estimation of the distribution of the NBG. An MT survey was conducted along three survey lines in this area. Each line trended east–west, perpendicular to the regional geological strike, and was composed of about 25 measurement sites. Induction vectors evaluated from the magnetic field show that this area has a two‐dimensional structure. The evaluated resistivity sections are in agreement with the log data. In conclusion, we were able to detect resistive layers (the NBG) below conductive layers. The results indicate that the NBG becomes gradually less resistive from north to south. In the centre of the northern line, an uplifted resistive area is interpreted as corresponding to the reservoir. By comparison with a seismic section, we prove the effectiveness of the integration of seismic and MT surveys for the investigation of the morphology and internal structure of the NBG. On other survey lines, the resistive uplifted zones are interpreted as possible prospective areas.

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JOGMEC/MOECO carried out an onshore seismic survey with explosive sources in 2012 in Cambodia.The project was executed under the Basic Agreement for the Study and Survey Program in Block XVII onshore Cambodia between JOGMEC and CNPA. This was the first experience of seismic data acquisition with explosives in Cambodia.Therefore, there were a lot of issues to be resolved before the field work was launched. One of most serious issues was the implementation of safe operations in a Mine/UXO contaminated eld. Other issues were a lack of regulations in Cambodia, education of non-experienced Cambodian people including both government staffs and local residents, explosive management and so on. Firstly JOGMEC/MOECO hired excellent Cambodian national staffs and further educated on seismic surveys. Then, they seriously and actively worked for communications with both government staffs and local residents. Such efforts resulted in good cooperation with all relevant parties even though unexpected procedures caused delays in the schedule. Finally, the seismic survey was successfully completed and no lost time for injury was recorded. A lot of knowledge on the seismic survey has been accumulated for all relevant parties through this experience. The procedures established by JOGMEC/MOECO through this survey will be one of the standards for onshore seismic data acquisitions in Cambodia.

Oil and gas explorations in mountainous regions are becoming more important to find unexplored possible reserves. Here, the seismic survey technique is a major exploration tool as well. However, difficulties often come from complicated topography change. For evaluating the topographic effects, we conducted the feasibility study for a 2D seismic survey in a particular mountainous area. In our study area, the locations where we can put sources or receivers are restricted, and it is possible to lay out dense sources and receivers on only one mountain road. Previously, reflection from mountainside or diffractions from topographic kink point were worried to damage reflection signals from subsurfaces. In this study, 3D acoustic wave simulation was conducted with the realistic topography model, and the calculated wavefield was examined. As the result, several different types of topography-related waves are identified. However, judging from this result and the other conditions, the seismic survey on a mountain ridge could be acceptable. And the acoustic simulator can be largely useful to the survey planning even though there were some limitations on the method.