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Stress state in the Cuu Long and Nam Con Son basins, offshore Vietnam |
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| Authors: | Nguyen Thi Thanh Binh Tomochika TokunagaNeil R Goulty Hoang Phuoc SonMai Van Binh |
| Institution: | a Department of Earth Sciences, Durham University, South Road, DH1 3LE, United Kingdom b Department of Environment Systems, School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8563, Japan c Con Son Joint Operating Company, Ho Chi Minh, Viet Nam |
| Abstract: | The results presented in this paper are the first published estimates of the complete stress tensor in the Cuu Long and Nam Con Son basins, offshore Vietnam. We analysed in situ stress and pore pressure fields in the sedimentary formations using data from petroleum exploration and production wells to evaluate the stress state in these basins. The data were obtained from the seafloor to 4300 m burial depth and include both hydrostatic and overpressured sections. Minimum horizontal stresses were obtained from extended leak-off tests and mini-fracture tests. Maximum horizontal stresses were estimated from drilling-induced fracture parameters and borehole breakout widths in twelve wells using rock properties measured in the laboratory or estimated empirically from wireline logs. Seven data points are located in sediments, and seventeen data points in igneous basement rocks at depths greater than 3000 m.The estimated magnitudes of σH are 70-110% of the σv magnitudes. Considering the errors in the stress magnitude estimates, their relative magnitudes suggest that a borderline normal/strike-slip stress regime presently exists in normally pressured sequences of the Nam Con Son and Cuu Long basins. Of the twenty-four data points, twenty have effective stress ratios at a critical stress state for faulting on the assumption that there are faults present that are optimally oriented for failure with friction coefficients of ∼0.5. The results suggest that the stress state in these basins is generally critical. |
| Keywords: | In situ stress Maximum horizontal stress Stress state Cuu Long Basin Nam Con Son Basin Vietnam |
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