1. Estimation of pore pressure, tectonic strain and stress magnitudes in the Upper Assam basin: a tectonically active part of India.
- Author
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Alam, Jenifer, Chatterjee, Rima, and Dasgupta, Sumangal
- Subjects
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PLATE tectonics , *STRUCTURAL geology , *OROGENIC belts , *EARTHQUAKES , *POROELASTICITY , *LITHOSPHERE - Abstract
Conventional well logs serve as effective tools for estimation of pore pressure (PP), tectonic strain and stress magnitudes in normal and thrust faulted parts of the Upper Assam basin. Several models have been developed for prediction of PP and stress magnitudes over the years. Acquiring tectonic strain in active area enhances the accuracy of in situ stress estimate in the Upper Assam. This paper discusses Eaton's sonic model for PP estimation and assesses stress magnitudes incorporating tectonic strain in poroelastic models. Eaton's exponent is varied from 0 to 3 to get best-fit results for PP prediction validated with available modular dynamic tester and mud weight data. PP is estimated for geological formations: Dhekiajuli, Girujan, Tipam, Barail, Kopili, Sylhet, Langpur to the granitic basement in normal and thrust faulted areas of the Upper Assam basin using Eaton's exponent of 1.0. The predicted tectonic strain using uniaxial model varies from −0.0044 to 0.0061. The computed tectonic strain using biaxial poroelastic model ranges from 0.000099 to 0.00077 along NE–SW and from −0.001 to −0.0019 along NW–SE directions for normal faulting regime, respectively. In thrust faulting regime, the tectonic strains are obtained as 0.00092 and 0.00053 along NE–SW and NW–SE directions, respectively. The vertical (S V), maximum (S H) and minimum (S h) horizontal stress gradients range 21.7–23.8, 14.9–23.1 and 12.0–21.4 MPa km−1, respectively. Moreover, we have proposed a multiple linear regression model for evaluation of S h from independent parameters, namely, PP, Poisson's ratio and S V from three wells and dependent parameter as leak-off test (LOT) data. This is further tested with other three wells in the study area. The predicted S h is found to have satisfactory correlation with observed LOT for these wells. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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