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- 저자 : ( Uy Vo ) (검색결과 3 건)
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Geomechanical characterization of sedimentary basins using tectonic stress and strai
Uy D. Vo,장찬동 한국지질과학협의회 2020 Geosciences Journal Vol.24 No.6
We examine whether the combination of tectonic stress and strain is useful in characterizing tectonic condition and geomechanics of sedimentary basins. We compile measured stress, pore pressure, and mechanical rock property data from six major sedimentary basins worldwide. We find that the measured horizontal principal stresses are always higher than the theoretically calculated stresses based on a simple uniaxial compaction poroelastic equation, known as Eaton’s model. From this we conclude that there are always external tectonic stresses in seemingly stable basins. We extract these external tectonic stresses by subtracting the theoretically calculated horizontal stresses from the measured horizontal stresses, and relate them to the tectonic strains estimated by the linear elastic constitutive model. Given the external tectonic stresses and associated strains, we interpret the tectonic conditions of individual basins from the tectonic differential stress and strain conditions. The six basins exhibit distinct tectonic stress and strain regimes, which can be related generally to geological processes such as brittle and ductile deformation. The results show that combining tectonic stress and strain is useful in characterizing sedimentary basins.
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A Case Study of Sand Production Prediction for a Wellbore Drilled in Cuu Long Basin, Vietnam
( Uy Vo ),( Chandong Chang ) 대한지질공학회 2016 대한지질공학회 학술발표회논문집 Vol.2016 No.1
Sand production is a type of wellbore rock failure process that causes a variety of borehole problems in petroleum industry such as stuck pipe, tubing erosion and well collapse. Thus we have to avoid sand production by controlling wellbore pressure for given ambient conditions such as stress states and rock strength. To predict excessive sand production, petroleum industry and science community have previously attempted a variety of techniques such as production history observation, mechanical property analysis, laboratory testing and computer modeling. In this study, we use poroelasticity theory to predict sand production in a wellbore drilled in Cuu-long basin, southeast Vietnam. The wellbore is 3873 m deep (TVD and 4471 m MD), penetrating into Oligocene sandstone formations. The sandstones are well cemented and consolidated with a UCS (unconfined compressive strength) range between 12 and 90 MPa. Since the rock formations are generally strong, we expect that there would be no severe sand production. Since the cased borehole required perforations to enhance the productivity, however, it is beneficial to investigate the sand production potential at the perforation depths. To that end, we used a geomechanical model including the stress states in formations and rock strength to find out the specific depths where sands would spall out into the wellbore. Based on this result, drillers carried out perforation process only at depths where sand production potential is extremely low. To make sure whether these perforation depths are stable regarding sand production, we estimated the lower limits of wellbore pressure (Pw) that would prevent sand production for given formation pressures. The calculated lower Pw limit was determined to be close to zero, suggesting that the sanding-free zones are quite stable. We also investigated the effect of wellbore trajectory on sand production. The results demonstrate that as the wellbore deviates towards horizontal, the sand production potential becomes high, indicating the importance of well trajectory for wellbore stability.
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