HR: 0800h
AN: OS51A-0175    [Abstracts]
TI: Prediction of magnitude of minimum horizontal stress from extended leak-off test conducted by the riser vessel CHIKYU
AU: * Lin, W
EM: lin@jamstec.go.jp
AF: Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, 200 Monobe-Otsu, Nankoku, 783-8502, Japan
AU: Masago, H
EM: masagoh@jamstec.go.jp
AF: Center for Deep Earth Exploration (CDEX), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 3173-25 Showa-machi, Kanazawa-Ku, Yokohama, 236-0001, Japan
AU: Yamamoto, K
EM: yamamoto-koji@jogmec.go.jp
AF: Technology Research Center (TRC), Japan Oil, Gas and Metals National Corporation, 1-2- 2, Hamada Mihama-ku, Chiba, 261-0025, Japan
AU: Kawamura, Y
EM: kawamuray@jamstec.go.jp
AF: Center for Deep Earth Exploration (CDEX), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 3173-25 Showa-machi, Kanazawa-Ku, Yokohama, 236-0001, Japan
AU: Saito, S
EM: saito@jamstec.go.jp
AF: Institute for Research Earth Evolution (IFREE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, 237-0061, Japan
AU: Kinoshita, M
EM: masa@jamstec.go.jp
AF: Institute for Research Earth Evolution (IFREE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, 237-0061, Japan
AB: By means of introduction of the drilling vessel �gCHIKYU�h, riser drilling operations using mud fluid will be carried out in NanTroSEIZE Stage 2 for the first time as an oceanic scientific-drilling. For determining drilling operation parameter such as a mud density, a downhole experiment, leak-off test (LOT) or extended leak-off test (XLOT), is going to be implemented next to casing and cementing at each casing shoe during the drilling process. Data of the downhole experiment aimed for operation can also be used for an important scientific application to obtain in-situ stress information which is necessary for various cases of scientific drillings such as seismogenic zone drillings etc. In order to examine feasibility of the application of the LOT or XLOT data, we analyzed an example of XLOT conducted by the riser vessel CHIKYU during its Shimokita shakedown cruise, 2006; and then estimated magnitude of minimum principal stress in horizontal plane, Shmin. Moreover, we will propose the test procedures to possibly improve the quality of stress result from the applications of LOT or XLOT. The XLOT of Shimokita cruise was conducted under following conditions; 1180 m water depth, 525 mbsf (meter below seafloor) depth, 1030 kg/m3 fluid density (seawater) and 80 litter/min injection flow-rate. Estimated magnitude of the Shmin is equal to 18.3 MPa based on the assumption that fracture closure pressure balances with the minimum principal stress perpendicular to the fracture plane. For comparison, the vertical stress magnitude at the depth was estimated from density profile of core samples retrieved from the same borehole; and was equal to 20 MPa approximately. These two values can be considered to be not disagreement. Therefore, we can say that the XLOT data is valuable and practical for estimating the magnitude of minimum horizontal stress. From the viewpoint of determining stress magnitude, the XLOT is more essential rather than the LOT because it might be hardly to obtain reliable Shmin magnitude only by leak-off pressure which is exclusive stress-related parameter obtained from the latter. In addition, implementation of the LOT/XLOT multi-cycles (3 cycles) is preferable if possible. The first cycle with a lower maximum injection pressure is for knowing permeable property of the formation and for examining whether there is pre-existing fracture(s). The second cycle is a normal XLOT; and the third one is the repeat of the second one for confirm the pressure values obtained from the XLOTs.
DE: 3036 Ocean drilling
DE: 3094 Instruments and techniques
DE: 8168 Stresses: general
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting