In-situ Stress and Pore Pressure Fields in the North Cuu Long Basin, Offshore Vietnam

Abstract

Abstract Knowledge of the in-situ stress field is vital for planning optimum orientations of inclined and horizontal wells, for reservoir characterization, as well as for a better understanding of geodynamic processes and their effects on basin evolution. In this study, we analyzed in-situ stress and pore pressure fields of Pre-Cenozoic basement and cover strata in the northern part of the Cuu Long Basin, offshore Vietnam, for the first time, based on available data from petroleum exploration and exploitation wells. The directions of minimum and maximum horizontal stresses were evaluated from borehole breakout and drilling-induced tensile fracture orientations. The maximum horizontal stress is oriented approximately NNW-SSE to N-S, and the minimum horizontal stress is ENE-WSW to E-W orientation. The magnitude of overburden stress was determined from density logs. Minimum horizontal stress was analyzed from good quality extended leak-off tests and mini-falloff tests. Maximum horizontal stress was estimated using breakdown equation of hydraulic fracture. Pore pressure was measured by RFT and DST. Overpressured condition was found in the upper Oligocene, while other units showed nearly hydrostatic condition except for the depleted intervals due to production. The effect of pore pressure change on in-situ stress magnitude was established based on the data from depleted pore pressure zone. From the obtained results from this analysis, we can reasonably well delineate in-situ stress and pore pressure fields of the area.