Publication Date:
2013-01-19
Description:
[1] In-situ test of hydraulic fracturing (HF) provide the only way to observe in-situ stress magnitudes directly. The maximum and minimum horizontal stresses, S H max and S h min , are determined from critical borehole pressures, i.e., the reopening pressure P r and the shut-in pressure P s , etc, observed during the test. However, there is inevitably a discrepancy between actual and measured values of the critical pressures, and this discrepancy is very significant for P r . For effective measurement of P r , it is necessary for the fracturing system to have a sufficiently small compliance. A diagnostic procedure to evaluate whether the compliance of the employed fracturing system is appropriate for S H max determination from P r was developed. Furthermore, a new method for stress measurement not restricted by the system compliance and P r is herein proposed. In this method, the magnitudes and orientations of S H max and S h min are determined from (i) the cross-sectional shape of a core sample and (ii) P s obtained by the HF test performed near the core depth. These ideas were applied for stress measurement in a central region of the Kumano forearc baisn at a water depth of 2054 m using a 1.6 km riser hole drilled in the Integrated Ocean Drilling Program (IODP) Expedition 319. As a result, the stress decoupling through a boundary at 1285 meters below seafloor was detected. The boundary separates new upper layers and old lower ones with an age gap of ~1.8 Ma, which is possibly the accretionary prism. The stress state in the lower layers is consistent with that observed in the outer edge of accretionary prism.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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