The 11th International Symposium on Recent Advances in Exploration Geophysics (RAEG 2007)

An element free Galerkin method which does not require connectivity between elements and nodes is examined its efficiency for rock experiment. In this study, uni-axial tensile and compressive tests and collapse of cavity are examined. In this process, the rock specimen is assumed to heterogeneous assigned by Weibull distribution. Acoustic Emission which is microscopic behavior of the specimen agrees with laboratory tests, and failure mode of the specimen also agrees with general laboratory test results.

Marine controlled source electromagnetic method may be one of the most significant new technologies for hydrocarbon exploration. The promise for the technology lies in its ability to differentiate resistive, potentially oil-bearing intervals from surrounding, more conductive water-bearing units. The principle is the same as that used in well logging devices to identify hydrocarbon zones in well bores. The technique is not new but the capability to resolve relatively thin resistive intervals in the depth offers new promise to lower the risk through direct hydrocarbon indicators in conjunction with modern seismic methods. In this paper, we discuss the capability of marine CSEM method towards gas hydrate exploration by numerical studies of 1-D modeling and 2.5-D inversion.

Amplitude-versus-offset (AVO) attribute analysis becomes a defact-standard technique for the contemporary hydrocarbon exploration. A basic product for this analysis is angle sub stacks, such as so-called near and far, and sometime middle in order to evaluate an amplitude change along offset or incident angle. Detail study of AVO interpretation is facilitated by crossplotting AVO intercept (P0) and gradient (G) under Shuey’s two term approximation. Further elastic attributes are derived basically from those P0 and G. Estimation of the P0 and G is normally derived via least-square fit of a prestack-migrated seismic gather, which is transformed from offset into incident angle. A partial stack technique is commonly introduced to enhance signal-to-noise ratio (S/N) anticipating better estimation. This ultimate case of the partial stack is the angle sub stack utilizing for amplitude study at an interpretation. In this paper, we are using synthetic and real seismic data contaminated by Gaussian noise to demonstrate that P0 and G estimation based on angle sub stacks is as reliable as computed on a full gather. This implies our standard interpretation data in our hands will be enough for in-house calculation of P0 and G, which can be done by an interpretation workstation, and this contributes budget saving for further P0 and G based processing.

A new sensor tool for borehole deformation using a laser displacement sensor has been developed for stress orientation measurement at shallow depths. The new method for estimation of stress field using this tool is based on following principles: 1) The borehole drilled in a stress field is quasistatically deformed due to viscous property of rock around a borehole. 2) The orientation of maximum horizontal compressive stress (SHmax) is determined from a minor axis of an ellipse fitted to a deformed shape of borehole cross section. One of the advantages of this method to estimate stress orientation is a remarkably lower cost than existing methods, such as stress release and hydraulic fracturing methods. Radial displacements of the borehole wall under creep deformation are measured with the laser displacement sensor rotating continuously around a borehole axis. A total resolution of 0.7μm is achieved by stacking of several thousands data. A field performance test confirms that the new tool can detect the creep deformation, about ten μm increasing of the borehole radius in a measurement of half a day just after drilling. After the performance test, we applied this new method to active faults in order to evaluate stress state of the faults. In the measurement for the Kego fault in Fukuoka Prefecture, western Japan, the average orientation of SHmax is about N60°E for the two measurement point around the southern edge of the fault. The estimated orientation is found to be unfavorable for a strike slip on the Kego fault. In the application to the Atotsugawa fault, central Japan, the orientation of SHmax is estimated to be ENE-WSW by the measurements in a mine cavity near the fault. This orientation is consistent with the trend of the directions of P-axes of the focal mechanism solutions of ultra-micro earthquakes along the fault.